1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
use core::iter::{FromIterator, Iterator};
use core::mem::{self, ManuallyDrop};
use core::ops::{Deref, DerefMut};
use core::ptr::{self, NonNull};
use core::{cmp, fmt, hash, isize, slice, usize};

use alloc::{
    borrow::{Borrow, BorrowMut},
    boxed::Box,
    string::String,
    vec::Vec,
};

use crate::buf::{IntoIter, UninitSlice};
use crate::bytes::Vtable;
#[allow(unused)]
use crate::loom::sync::atomic::AtomicMut;
use crate::loom::sync::atomic::{self, AtomicPtr, AtomicUsize, Ordering};
use crate::{Buf, BufMut, Bytes};

/// A unique reference to a contiguous slice of memory.
///
/// `BytesMut` represents a unique view into a potentially shared memory region.
/// Given the uniqueness guarantee, owners of `BytesMut` handles are able to
/// mutate the memory.
///
/// `BytesMut` can be thought of as containing a `buf: Arc<Vec<u8>>`, an offset
/// into `buf`, a slice length, and a guarantee that no other `BytesMut` for the
/// same `buf` overlaps with its slice. That guarantee means that a write lock
/// is not required.
///
/// # Growth
///
/// `BytesMut`'s `BufMut` implementation will implicitly grow its buffer as
/// necessary. However, explicitly reserving the required space up-front before
/// a series of inserts will be more efficient.
///
/// # Examples
///
/// ```
/// use bytes::{BytesMut, BufMut};
///
/// let mut buf = BytesMut::with_capacity(64);
///
/// buf.put_u8(b'h');
/// buf.put_u8(b'e');
/// buf.put(&b"llo"[..]);
///
/// assert_eq!(&buf[..], b"hello");
///
/// // Freeze the buffer so that it can be shared
/// let a = buf.freeze();
///
/// // This does not allocate, instead `b` points to the same memory.
/// let b = a.clone();
///
/// assert_eq!(&a[..], b"hello");
/// assert_eq!(&b[..], b"hello");
/// ```
pub struct BytesMut {
    ptr: NonNull<u8>,
    len: usize,
    cap: usize,
    data: *mut Shared,
}

// Thread-safe reference-counted container for the shared storage. This mostly
// the same as `core::sync::Arc` but without the weak counter. The ref counting
// fns are based on the ones found in `std`.
//
// The main reason to use `Shared` instead of `core::sync::Arc` is that it ends
// up making the overall code simpler and easier to reason about. This is due to
// some of the logic around setting `Inner::arc` and other ways the `arc` field
// is used. Using `Arc` ended up requiring a number of funky transmutes and
// other shenanigans to make it work.
struct Shared {
    vec: Vec<u8>,
    original_capacity_repr: usize,
    ref_count: AtomicUsize,
}

// Buffer storage strategy flags.
const KIND_ARC: usize = 0b0;
const KIND_VEC: usize = 0b1;
const KIND_MASK: usize = 0b1;

// The max original capacity value. Any `Bytes` allocated with a greater initial
// capacity will default to this.
const MAX_ORIGINAL_CAPACITY_WIDTH: usize = 17;
// The original capacity algorithm will not take effect unless the originally
// allocated capacity was at least 1kb in size.
const MIN_ORIGINAL_CAPACITY_WIDTH: usize = 10;
// The original capacity is stored in powers of 2 starting at 1kb to a max of
// 64kb. Representing it as such requires only 3 bits of storage.
const ORIGINAL_CAPACITY_MASK: usize = 0b11100;
const ORIGINAL_CAPACITY_OFFSET: usize = 2;

// When the storage is in the `Vec` representation, the pointer can be advanced
// at most this value. This is due to the amount of storage available to track
// the offset is usize - number of KIND bits and number of ORIGINAL_CAPACITY
// bits.
const VEC_POS_OFFSET: usize = 5;
const MAX_VEC_POS: usize = usize::MAX >> VEC_POS_OFFSET;
const NOT_VEC_POS_MASK: usize = 0b11111;

#[cfg(target_pointer_width = "64")]
const PTR_WIDTH: usize = 64;
#[cfg(target_pointer_width = "32")]
const PTR_WIDTH: usize = 32;

/*
 *
 * ===== BytesMut =====
 *
 */

impl BytesMut {
    /// Creates a new `BytesMut` with the specified capacity.
    ///
    /// The returned `BytesMut` will be able to hold at least `capacity` bytes
    /// without reallocating.
    ///
    /// It is important to note that this function does not specify the length
    /// of the returned `BytesMut`, but only the capacity.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut bytes = BytesMut::with_capacity(64);
    ///
    /// // `bytes` contains no data, even though there is capacity
    /// assert_eq!(bytes.len(), 0);
    ///
    /// bytes.put(&b"hello world"[..]);
    ///
    /// assert_eq!(&bytes[..], b"hello world");
    /// ```
    #[inline]
    pub fn with_capacity(capacity: usize) -> BytesMut {
        BytesMut::from_vec(Vec::with_capacity(capacity))
    }

    /// Creates a new `BytesMut` with default capacity.
    ///
    /// Resulting object has length 0 and unspecified capacity.
    /// This function does not allocate.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut bytes = BytesMut::new();
    ///
    /// assert_eq!(0, bytes.len());
    ///
    /// bytes.reserve(2);
    /// bytes.put_slice(b"xy");
    ///
    /// assert_eq!(&b"xy"[..], &bytes[..]);
    /// ```
    #[inline]
    pub fn new() -> BytesMut {
        BytesMut::with_capacity(0)
    }

    /// Returns the number of bytes contained in this `BytesMut`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::from(&b"hello"[..]);
    /// assert_eq!(b.len(), 5);
    /// ```
    #[inline]
    pub fn len(&self) -> usize {
        self.len
    }

    /// Returns true if the `BytesMut` has a length of 0.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::with_capacity(64);
    /// assert!(b.is_empty());
    /// ```
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len == 0
    }

    /// Returns the number of bytes the `BytesMut` can hold without reallocating.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::with_capacity(64);
    /// assert_eq!(b.capacity(), 64);
    /// ```
    #[inline]
    pub fn capacity(&self) -> usize {
        self.cap
    }

    /// Converts `self` into an immutable `Bytes`.
    ///
    /// The conversion is zero cost and is used to indicate that the slice
    /// referenced by the handle will no longer be mutated. Once the conversion
    /// is done, the handle can be cloned and shared across threads.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    /// use std::thread;
    ///
    /// let mut b = BytesMut::with_capacity(64);
    /// b.put(&b"hello world"[..]);
    /// let b1 = b.freeze();
    /// let b2 = b1.clone();
    ///
    /// let th = thread::spawn(move || {
    ///     assert_eq!(&b1[..], b"hello world");
    /// });
    ///
    /// assert_eq!(&b2[..], b"hello world");
    /// th.join().unwrap();
    /// ```
    #[inline]
    pub fn freeze(mut self) -> Bytes {
        if self.kind() == KIND_VEC {
            // Just re-use `Bytes` internal Vec vtable
            unsafe {
                let (off, _) = self.get_vec_pos();
                let vec = rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off);
                mem::forget(self);
                let mut b: Bytes = vec.into();
                b.advance(off);
                b
            }
        } else {
            debug_assert_eq!(self.kind(), KIND_ARC);

            let ptr = self.ptr.as_ptr();
            let len = self.len;
            let data = AtomicPtr::new(self.data as _);
            mem::forget(self);
            unsafe { Bytes::with_vtable(ptr, len, data, &SHARED_VTABLE) }
        }
    }

    /// Splits the bytes into two at the given index.
    ///
    /// Afterwards `self` contains elements `[0, at)`, and the returned
    /// `BytesMut` contains elements `[at, capacity)`.
    ///
    /// This is an `O(1)` operation that just increases the reference count
    /// and sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut a = BytesMut::from(&b"hello world"[..]);
    /// let mut b = a.split_off(5);
    ///
    /// a[0] = b'j';
    /// b[0] = b'!';
    ///
    /// assert_eq!(&a[..], b"jello");
    /// assert_eq!(&b[..], b"!world");
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if `at > capacity`.
    #[must_use = "consider BytesMut::truncate if you don't need the other half"]
    pub fn split_off(&mut self, at: usize) -> BytesMut {
        assert!(
            at <= self.capacity(),
            "split_off out of bounds: {:?} <= {:?}",
            at,
            self.capacity(),
        );
        unsafe {
            let mut other = self.shallow_clone();
            other.set_start(at);
            self.set_end(at);
            other
        }
    }

    /// Removes the bytes from the current view, returning them in a new
    /// `BytesMut` handle.
    ///
    /// Afterwards, `self` will be empty, but will retain any additional
    /// capacity that it had before the operation. This is identical to
    /// `self.split_to(self.len())`.
    ///
    /// This is an `O(1)` operation that just increases the reference count and
    /// sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut buf = BytesMut::with_capacity(1024);
    /// buf.put(&b"hello world"[..]);
    ///
    /// let other = buf.split();
    ///
    /// assert!(buf.is_empty());
    /// assert_eq!(1013, buf.capacity());
    ///
    /// assert_eq!(other, b"hello world"[..]);
    /// ```
    #[must_use = "consider BytesMut::advance(len()) if you don't need the other half"]
    pub fn split(&mut self) -> BytesMut {
        let len = self.len();
        self.split_to(len)
    }

    /// Splits the buffer into two at the given index.
    ///
    /// Afterwards `self` contains elements `[at, len)`, and the returned `BytesMut`
    /// contains elements `[0, at)`.
    ///
    /// This is an `O(1)` operation that just increases the reference count and
    /// sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut a = BytesMut::from(&b"hello world"[..]);
    /// let mut b = a.split_to(5);
    ///
    /// a[0] = b'!';
    /// b[0] = b'j';
    ///
    /// assert_eq!(&a[..], b"!world");
    /// assert_eq!(&b[..], b"jello");
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if `at > len`.
    #[must_use = "consider BytesMut::advance if you don't need the other half"]
    pub fn split_to(&mut self, at: usize) -> BytesMut {
        assert!(
            at <= self.len(),
            "split_to out of bounds: {:?} <= {:?}",
            at,
            self.len(),
        );

        unsafe {
            let mut other = self.shallow_clone();
            other.set_end(at);
            self.set_start(at);
            other
        }
    }

    /// Shortens the buffer, keeping the first `len` bytes and dropping the
    /// rest.
    ///
    /// If `len` is greater than the buffer's current length, this has no
    /// effect.
    ///
    /// The [`split_off`] method can emulate `truncate`, but this causes the
    /// excess bytes to be returned instead of dropped.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello world"[..]);
    /// buf.truncate(5);
    /// assert_eq!(buf, b"hello"[..]);
    /// ```
    ///
    /// [`split_off`]: #method.split_off
    pub fn truncate(&mut self, len: usize) {
        if len <= self.len() {
            unsafe {
                self.set_len(len);
            }
        }
    }

    /// Clears the buffer, removing all data.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello world"[..]);
    /// buf.clear();
    /// assert!(buf.is_empty());
    /// ```
    pub fn clear(&mut self) {
        self.truncate(0);
    }

    /// Resizes the buffer so that `len` is equal to `new_len`.
    ///
    /// If `new_len` is greater than `len`, the buffer is extended by the
    /// difference with each additional byte set to `value`. If `new_len` is
    /// less than `len`, the buffer is simply truncated.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::new();
    ///
    /// buf.resize(3, 0x1);
    /// assert_eq!(&buf[..], &[0x1, 0x1, 0x1]);
    ///
    /// buf.resize(2, 0x2);
    /// assert_eq!(&buf[..], &[0x1, 0x1]);
    ///
    /// buf.resize(4, 0x3);
    /// assert_eq!(&buf[..], &[0x1, 0x1, 0x3, 0x3]);
    /// ```
    pub fn resize(&mut self, new_len: usize, value: u8) {
        let len = self.len();
        if new_len > len {
            let additional = new_len - len;
            self.reserve(additional);
            unsafe {
                let dst = self.chunk_mut().as_mut_ptr();
                ptr::write_bytes(dst, value, additional);
                self.set_len(new_len);
            }
        } else {
            self.truncate(new_len);
        }
    }

    /// Sets the length of the buffer.
    ///
    /// This will explicitly set the size of the buffer without actually
    /// modifying the data, so it is up to the caller to ensure that the data
    /// has been initialized.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut b = BytesMut::from(&b"hello world"[..]);
    ///
    /// unsafe {
    ///     b.set_len(5);
    /// }
    ///
    /// assert_eq!(&b[..], b"hello");
    ///
    /// unsafe {
    ///     b.set_len(11);
    /// }
    ///
    /// assert_eq!(&b[..], b"hello world");
    /// ```
    #[inline]
    pub unsafe fn set_len(&mut self, len: usize) {
        debug_assert!(len <= self.cap, "set_len out of bounds");
        self.len = len;
    }

    /// Reserves capacity for at least `additional` more bytes to be inserted
    /// into the given `BytesMut`.
    ///
    /// More than `additional` bytes may be reserved in order to avoid frequent
    /// reallocations. A call to `reserve` may result in an allocation.
    ///
    /// Before allocating new buffer space, the function will attempt to reclaim
    /// space in the existing buffer. If the current handle references a small
    /// view in the original buffer and all other handles have been dropped,
    /// and the requested capacity is less than or equal to the existing
    /// buffer's capacity, then the current view will be copied to the front of
    /// the buffer and the handle will take ownership of the full buffer.
    ///
    /// # Examples
    ///
    /// In the following example, a new buffer is allocated.
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello"[..]);
    /// buf.reserve(64);
    /// assert!(buf.capacity() >= 69);
    /// ```
    ///
    /// In the following example, the existing buffer is reclaimed.
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut buf = BytesMut::with_capacity(128);
    /// buf.put(&[0; 64][..]);
    ///
    /// let ptr = buf.as_ptr();
    /// let other = buf.split();
    ///
    /// assert!(buf.is_empty());
    /// assert_eq!(buf.capacity(), 64);
    ///
    /// drop(other);
    /// buf.reserve(128);
    ///
    /// assert_eq!(buf.capacity(), 128);
    /// assert_eq!(buf.as_ptr(), ptr);
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `usize`.
    #[inline]
    pub fn reserve(&mut self, additional: usize) {
        let len = self.len();
        let rem = self.capacity() - len;

        if additional <= rem {
            // The handle can already store at least `additional` more bytes, so
            // there is no further work needed to be done.
            return;
        }

        self.reserve_inner(additional);
    }

    // In separate function to allow the short-circuits in `reserve` to
    // be inline-able. Significant helps performance.
    fn reserve_inner(&mut self, additional: usize) {
        let len = self.len();
        let kind = self.kind();

        if kind == KIND_VEC {
            // If there's enough free space before the start of the buffer, then
            // just copy the data backwards and reuse the already-allocated
            // space.
            //
            // Otherwise, since backed by a vector, use `Vec::reserve`
            unsafe {
                let (off, prev) = self.get_vec_pos();

                // Only reuse space if we can satisfy the requested additional space.
                if self.capacity() - self.len() + off >= additional {
                    // There's space - reuse it
                    //
                    // Just move the pointer back to the start after copying
                    // data back.
                    let base_ptr = self.ptr.as_ptr().offset(-(off as isize));
                    ptr::copy(self.ptr.as_ptr(), base_ptr, self.len);
                    self.ptr = vptr(base_ptr);
                    self.set_vec_pos(0, prev);

                    // Length stays constant, but since we moved backwards we
                    // can gain capacity back.
                    self.cap += off;
                } else {
                    // No space - allocate more
                    let mut v =
                        ManuallyDrop::new(rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off));
                    v.reserve(additional);

                    // Update the info
                    self.ptr = vptr(v.as_mut_ptr().offset(off as isize));
                    self.len = v.len() - off;
                    self.cap = v.capacity() - off;
                }

                return;
            }
        }

        debug_assert_eq!(kind, KIND_ARC);
        let shared: *mut Shared = self.data as _;

        // Reserving involves abandoning the currently shared buffer and
        // allocating a new vector with the requested capacity.
        //
        // Compute the new capacity
        let mut new_cap = len.checked_add(additional).expect("overflow");

        let original_capacity;
        let original_capacity_repr;

        unsafe {
            original_capacity_repr = (*shared).original_capacity_repr;
            original_capacity = original_capacity_from_repr(original_capacity_repr);

            // First, try to reclaim the buffer. This is possible if the current
            // handle is the only outstanding handle pointing to the buffer.
            if (*shared).is_unique() {
                // This is the only handle to the buffer. It can be reclaimed.
                // However, before doing the work of copying data, check to make
                // sure that the vector has enough capacity.
                let v = &mut (*shared).vec;

                if v.capacity() >= new_cap {
                    // The capacity is sufficient, reclaim the buffer
                    let ptr = v.as_mut_ptr();

                    ptr::copy(self.ptr.as_ptr(), ptr, len);

                    self.ptr = vptr(ptr);
                    self.cap = v.capacity();

                    return;
                }

                // The vector capacity is not sufficient. The reserve request is
                // asking for more than the initial buffer capacity. Allocate more
                // than requested if `new_cap` is not much bigger than the current
                // capacity.
                //
                // There are some situations, using `reserve_exact` that the
                // buffer capacity could be below `original_capacity`, so do a
                // check.
                let double = v.capacity().checked_shl(1).unwrap_or(new_cap);

                new_cap = cmp::max(cmp::max(double, new_cap), original_capacity);
            } else {
                new_cap = cmp::max(new_cap, original_capacity);
            }
        }

        // Create a new vector to store the data
        let mut v = ManuallyDrop::new(Vec::with_capacity(new_cap));

        // Copy the bytes
        v.extend_from_slice(self.as_ref());

        // Release the shared handle. This must be done *after* the bytes are
        // copied.
        unsafe { release_shared(shared) };

        // Update self
        let data = (original_capacity_repr << ORIGINAL_CAPACITY_OFFSET) | KIND_VEC;
        self.data = data as _;
        self.ptr = vptr(v.as_mut_ptr());
        self.len = v.len();
        self.cap = v.capacity();
    }

    /// Appends given bytes to this `BytesMut`.
    ///
    /// If this `BytesMut` object does not have enough capacity, it is resized
    /// first.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::with_capacity(0);
    /// buf.extend_from_slice(b"aaabbb");
    /// buf.extend_from_slice(b"cccddd");
    ///
    /// assert_eq!(b"aaabbbcccddd", &buf[..]);
    /// ```
    pub fn extend_from_slice(&mut self, extend: &[u8]) {
        let cnt = extend.len();
        self.reserve(cnt);

        unsafe {
            let dst = self.uninit_slice();
            // Reserved above
            debug_assert!(dst.len() >= cnt);

            ptr::copy_nonoverlapping(extend.as_ptr(), dst.as_mut_ptr() as *mut u8, cnt);
        }

        unsafe {
            self.advance_mut(cnt);
        }
    }

    /// Absorbs a `BytesMut` that was previously split off.
    ///
    /// If the two `BytesMut` objects were previously contiguous, i.e., if
    /// `other` was created by calling `split_off` on this `BytesMut`, then
    /// this is an `O(1)` operation that just decreases a reference
    /// count and sets a few indices. Otherwise this method degenerates to
    /// `self.extend_from_slice(other.as_ref())`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::with_capacity(64);
    /// buf.extend_from_slice(b"aaabbbcccddd");
    ///
    /// let split = buf.split_off(6);
    /// assert_eq!(b"aaabbb", &buf[..]);
    /// assert_eq!(b"cccddd", &split[..]);
    ///
    /// buf.unsplit(split);
    /// assert_eq!(b"aaabbbcccddd", &buf[..]);
    /// ```
    pub fn unsplit(&mut self, other: BytesMut) {
        if self.is_empty() {
            *self = other;
            return;
        }

        if let Err(other) = self.try_unsplit(other) {
            self.extend_from_slice(other.as_ref());
        }
    }

    // private

    // For now, use a `Vec` to manage the memory for us, but we may want to
    // change that in the future to some alternate allocator strategy.
    //
    // Thus, we don't expose an easy way to construct from a `Vec` since an
    // internal change could make a simple pattern (`BytesMut::from(vec)`)
    // suddenly a lot more expensive.
    #[inline]
    pub(crate) fn from_vec(mut vec: Vec<u8>) -> BytesMut {
        let ptr = vptr(vec.as_mut_ptr());
        let len = vec.len();
        let cap = vec.capacity();
        mem::forget(vec);

        let original_capacity_repr = original_capacity_to_repr(cap);
        let data = (original_capacity_repr << ORIGINAL_CAPACITY_OFFSET) | KIND_VEC;

        BytesMut {
            ptr,
            len,
            cap,
            data: data as *mut _,
        }
    }

    #[inline]
    fn as_slice(&self) -> &[u8] {
        unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len) }
    }

    #[inline]
    fn as_slice_mut(&mut self) -> &mut [u8] {
        unsafe { slice::from_raw_parts_mut(self.ptr.as_ptr(), self.len) }
    }

    unsafe fn set_start(&mut self, start: usize) {
        // Setting the start to 0 is a no-op, so return early if this is the
        // case.
        if start == 0 {
            return;
        }

        debug_assert!(start <= self.cap, "internal: set_start out of bounds");

        let kind = self.kind();

        if kind == KIND_VEC {
            // Setting the start when in vec representation is a little more
            // complicated. First, we have to track how far ahead the
            // "start" of the byte buffer from the beginning of the vec. We
            // also have to ensure that we don't exceed the maximum shift.
            let (mut pos, prev) = self.get_vec_pos();
            pos += start;

            if pos <= MAX_VEC_POS {
                self.set_vec_pos(pos, prev);
            } else {
                // The repr must be upgraded to ARC. This will never happen
                // on 64 bit systems and will only happen on 32 bit systems
                // when shifting past 134,217,727 bytes. As such, we don't
                // worry too much about performance here.
                self.promote_to_shared(/*ref_count = */ 1);
            }
        }

        // Updating the start of the view is setting `ptr` to point to the
        // new start and updating the `len` field to reflect the new length
        // of the view.
        self.ptr = vptr(self.ptr.as_ptr().offset(start as isize));

        if self.len >= start {
            self.len -= start;
        } else {
            self.len = 0;
        }

        self.cap -= start;
    }

    unsafe fn set_end(&mut self, end: usize) {
        debug_assert_eq!(self.kind(), KIND_ARC);
        assert!(end <= self.cap, "set_end out of bounds");

        self.cap = end;
        self.len = cmp::min(self.len, end);
    }

    fn try_unsplit(&mut self, other: BytesMut) -> Result<(), BytesMut> {
        if other.is_empty() {
            return Ok(());
        }

        let ptr = unsafe { self.ptr.as_ptr().offset(self.len as isize) };
        if ptr == other.ptr.as_ptr()
            && self.kind() == KIND_ARC
            && other.kind() == KIND_ARC
            && self.data == other.data
        {
            // Contiguous blocks, just combine directly
            self.len += other.len;
            self.cap += other.cap;
            Ok(())
        } else {
            Err(other)
        }
    }

    #[inline]
    fn kind(&self) -> usize {
        self.data as usize & KIND_MASK
    }

    unsafe fn promote_to_shared(&mut self, ref_cnt: usize) {
        debug_assert_eq!(self.kind(), KIND_VEC);
        debug_assert!(ref_cnt == 1 || ref_cnt == 2);

        let original_capacity_repr =
            (self.data as usize & ORIGINAL_CAPACITY_MASK) >> ORIGINAL_CAPACITY_OFFSET;

        // The vec offset cannot be concurrently mutated, so there
        // should be no danger reading it.
        let off = (self.data as usize) >> VEC_POS_OFFSET;

        // First, allocate a new `Shared` instance containing the
        // `Vec` fields. It's important to note that `ptr`, `len`,
        // and `cap` cannot be mutated without having `&mut self`.
        // This means that these fields will not be concurrently
        // updated and since the buffer hasn't been promoted to an
        // `Arc`, those three fields still are the components of the
        // vector.
        let shared = Box::new(Shared {
            vec: rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off),
            original_capacity_repr,
            ref_count: AtomicUsize::new(ref_cnt),
        });

        let shared = Box::into_raw(shared);

        // The pointer should be aligned, so this assert should
        // always succeed.
        debug_assert_eq!(shared as usize & KIND_MASK, KIND_ARC);

        self.data = shared as _;
    }

    /// Makes an exact shallow clone of `self`.
    ///
    /// The kind of `self` doesn't matter, but this is unsafe
    /// because the clone will have the same offsets. You must
    /// be sure the returned value to the user doesn't allow
    /// two views into the same range.
    #[inline]
    unsafe fn shallow_clone(&mut self) -> BytesMut {
        if self.kind() == KIND_ARC {
            increment_shared(self.data);
            ptr::read(self)
        } else {
            self.promote_to_shared(/*ref_count = */ 2);
            ptr::read(self)
        }
    }

    #[inline]
    unsafe fn get_vec_pos(&mut self) -> (usize, usize) {
        debug_assert_eq!(self.kind(), KIND_VEC);

        let prev = self.data as usize;
        (prev >> VEC_POS_OFFSET, prev)
    }

    #[inline]
    unsafe fn set_vec_pos(&mut self, pos: usize, prev: usize) {
        debug_assert_eq!(self.kind(), KIND_VEC);
        debug_assert!(pos <= MAX_VEC_POS);

        self.data = ((pos << VEC_POS_OFFSET) | (prev & NOT_VEC_POS_MASK)) as *mut _;
    }

    #[inline]
    fn uninit_slice(&mut self) -> &mut UninitSlice {
        unsafe {
            let ptr = self.ptr.as_ptr().offset(self.len as isize);
            let len = self.cap - self.len;

            UninitSlice::from_raw_parts_mut(ptr, len)
        }
    }
}

impl Drop for BytesMut {
    fn drop(&mut self) {
        let kind = self.kind();

        if kind == KIND_VEC {
            unsafe {
                let (off, _) = self.get_vec_pos();

                // Vector storage, free the vector
                let _ = rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off);
            }
        } else if kind == KIND_ARC {
            unsafe { release_shared(self.data as _) };
        }
    }
}

impl Buf for BytesMut {
    #[inline]
    fn remaining(&self) -> usize {
        self.len()
    }

    #[inline]
    fn chunk(&self) -> &[u8] {
        self.as_slice()
    }

    #[inline]
    fn advance(&mut self, cnt: usize) {
        assert!(
            cnt <= self.remaining(),
            "cannot advance past `remaining`: {:?} <= {:?}",
            cnt,
            self.remaining(),
        );
        unsafe {
            self.set_start(cnt);
        }
    }

    fn copy_to_bytes(&mut self, len: usize) -> crate::Bytes {
        self.split_to(len).freeze()
    }
}

unsafe impl BufMut for BytesMut {
    #[inline]
    fn remaining_mut(&self) -> usize {
        usize::MAX - self.len()
    }

    #[inline]
    unsafe fn advance_mut(&mut self, cnt: usize) {
        let new_len = self.len() + cnt;
        assert!(
            new_len <= self.cap,
            "new_len = {}; capacity = {}",
            new_len,
            self.cap
        );
        self.len = new_len;
    }

    #[inline]
    fn chunk_mut(&mut self) -> &mut UninitSlice {
        if self.capacity() == self.len() {
            self.reserve(64);
        }
        self.uninit_slice()
    }

    // Specialize these methods so they can skip checking `remaining_mut`
    // and `advance_mut`.

    fn put<T: crate::Buf>(&mut self, mut src: T)
    where
        Self: Sized,
    {
        while src.has_remaining() {
            let s = src.chunk();
            let l = s.len();
            self.extend_from_slice(s);
            src.advance(l);
        }
    }

    fn put_slice(&mut self, src: &[u8]) {
        self.extend_from_slice(src);
    }
}

impl AsRef<[u8]> for BytesMut {
    #[inline]
    fn as_ref(&self) -> &[u8] {
        self.as_slice()
    }
}

impl Deref for BytesMut {
    type Target = [u8];

    #[inline]
    fn deref(&self) -> &[u8] {
        self.as_ref()
    }
}

impl AsMut<[u8]> for BytesMut {
    #[inline]
    fn as_mut(&mut self) -> &mut [u8] {
        self.as_slice_mut()
    }
}

impl DerefMut for BytesMut {
    #[inline]
    fn deref_mut(&mut self) -> &mut [u8] {
        self.as_mut()
    }
}

impl<'a> From<&'a [u8]> for BytesMut {
    fn from(src: &'a [u8]) -> BytesMut {
        BytesMut::from_vec(src.to_vec())
    }
}

impl<'a> From<&'a str> for BytesMut {
    fn from(src: &'a str) -> BytesMut {
        BytesMut::from(src.as_bytes())
    }
}

impl From<BytesMut> for Bytes {
    fn from(src: BytesMut) -> Bytes {
        src.freeze()
    }
}

impl PartialEq for BytesMut {
    fn eq(&self, other: &BytesMut) -> bool {
        self.as_slice() == other.as_slice()
    }
}

impl PartialOrd for BytesMut {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        self.as_slice().partial_cmp(other.as_slice())
    }
}

impl Ord for BytesMut {
    fn cmp(&self, other: &BytesMut) -> cmp::Ordering {
        self.as_slice().cmp(other.as_slice())
    }
}

impl Eq for BytesMut {}

impl Default for BytesMut {
    #[inline]
    fn default() -> BytesMut {
        BytesMut::new()
    }
}

impl hash::Hash for BytesMut {
    fn hash<H>(&self, state: &mut H)
    where
        H: hash::Hasher,
    {
        let s: &[u8] = self.as_ref();
        s.hash(state);
    }
}

impl Borrow<[u8]> for BytesMut {
    fn borrow(&self) -> &[u8] {
        self.as_ref()
    }
}

impl BorrowMut<[u8]> for BytesMut {
    fn borrow_mut(&mut self) -> &mut [u8] {
        self.as_mut()
    }
}

impl fmt::Write for BytesMut {
    #[inline]
    fn write_str(&mut self, s: &str) -> fmt::Result {
        if self.remaining_mut() >= s.len() {
            self.put_slice(s.as_bytes());
            Ok(())
        } else {
            Err(fmt::Error)
        }
    }

    #[inline]
    fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> fmt::Result {
        fmt::write(self, args)
    }
}

impl Clone for BytesMut {
    fn clone(&self) -> BytesMut {
        BytesMut::from(&self[..])
    }
}

impl IntoIterator for BytesMut {
    type Item = u8;
    type IntoIter = IntoIter<BytesMut>;

    fn into_iter(self) -> Self::IntoIter {
        IntoIter::new(self)
    }
}

impl<'a> IntoIterator for &'a BytesMut {
    type Item = &'a u8;
    type IntoIter = core::slice::Iter<'a, u8>;

    fn into_iter(self) -> Self::IntoIter {
        self.as_ref().into_iter()
    }
}

impl Extend<u8> for BytesMut {
    fn extend<T>(&mut self, iter: T)
    where
        T: IntoIterator<Item = u8>,
    {
        let iter = iter.into_iter();

        let (lower, _) = iter.size_hint();
        self.reserve(lower);

        // TODO: optimize
        // 1. If self.kind() == KIND_VEC, use Vec::extend
        // 2. Make `reserve` inline-able
        for b in iter {
            self.reserve(1);
            self.put_u8(b);
        }
    }
}

impl<'a> Extend<&'a u8> for BytesMut {
    fn extend<T>(&mut self, iter: T)
    where
        T: IntoIterator<Item = &'a u8>,
    {
        self.extend(iter.into_iter().map(|b| *b))
    }
}

impl FromIterator<u8> for BytesMut {
    fn from_iter<T: IntoIterator<Item = u8>>(into_iter: T) -> Self {
        BytesMut::from_vec(Vec::from_iter(into_iter))
    }
}

impl<'a> FromIterator<&'a u8> for BytesMut {
    fn from_iter<T: IntoIterator<Item = &'a u8>>(into_iter: T) -> Self {
        BytesMut::from_iter(into_iter.into_iter().map(|b| *b))
    }
}

/*
 *
 * ===== Inner =====
 *
 */

unsafe fn increment_shared(ptr: *mut Shared) {
    let old_size = (*ptr).ref_count.fetch_add(1, Ordering::Relaxed);

    if old_size > isize::MAX as usize {
        crate::abort();
    }
}

unsafe fn release_shared(ptr: *mut Shared) {
    // `Shared` storage... follow the drop steps from Arc.
    if (*ptr).ref_count.fetch_sub(1, Ordering::Release) != 1 {
        return;
    }

    // This fence is needed to prevent reordering of use of the data and
    // deletion of the data.  Because it is marked `Release`, the decreasing
    // of the reference count synchronizes with this `Acquire` fence. This
    // means that use of the data happens before decreasing the reference
    // count, which happens before this fence, which happens before the
    // deletion of the data.
    //
    // As explained in the [Boost documentation][1],
    //
    // > It is important to enforce any possible access to the object in one
    // > thread (through an existing reference) to *happen before* deleting
    // > the object in a different thread. This is achieved by a "release"
    // > operation after dropping a reference (any access to the object
    // > through this reference must obviously happened before), and an
    // > "acquire" operation before deleting the object.
    //
    // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
    atomic::fence(Ordering::Acquire);

    // Drop the data
    Box::from_raw(ptr);
}

impl Shared {
    fn is_unique(&self) -> bool {
        // The goal is to check if the current handle is the only handle
        // that currently has access to the buffer. This is done by
        // checking if the `ref_count` is currently 1.
        //
        // The `Acquire` ordering synchronizes with the `Release` as
        // part of the `fetch_sub` in `release_shared`. The `fetch_sub`
        // operation guarantees that any mutations done in other threads
        // are ordered before the `ref_count` is decremented. As such,
        // this `Acquire` will guarantee that those mutations are
        // visible to the current thread.
        self.ref_count.load(Ordering::Acquire) == 1
    }
}

fn original_capacity_to_repr(cap: usize) -> usize {
    let width = PTR_WIDTH - ((cap >> MIN_ORIGINAL_CAPACITY_WIDTH).leading_zeros() as usize);
    cmp::min(
        width,
        MAX_ORIGINAL_CAPACITY_WIDTH - MIN_ORIGINAL_CAPACITY_WIDTH,
    )
}

fn original_capacity_from_repr(repr: usize) -> usize {
    if repr == 0 {
        return 0;
    }

    1 << (repr + (MIN_ORIGINAL_CAPACITY_WIDTH - 1))
}

/*
#[test]
fn test_original_capacity_to_repr() {
    assert_eq!(original_capacity_to_repr(0), 0);

    let max_width = 32;

    for width in 1..(max_width + 1) {
        let cap = 1 << width - 1;

        let expected = if width < MIN_ORIGINAL_CAPACITY_WIDTH {
            0
        } else if width < MAX_ORIGINAL_CAPACITY_WIDTH {
            width - MIN_ORIGINAL_CAPACITY_WIDTH
        } else {
            MAX_ORIGINAL_CAPACITY_WIDTH - MIN_ORIGINAL_CAPACITY_WIDTH
        };

        assert_eq!(original_capacity_to_repr(cap), expected);

        if width > 1 {
            assert_eq!(original_capacity_to_repr(cap + 1), expected);
        }

        //  MIN_ORIGINAL_CAPACITY_WIDTH must be bigger than 7 to pass tests below
        if width == MIN_ORIGINAL_CAPACITY_WIDTH + 1 {
            assert_eq!(original_capacity_to_repr(cap - 24), expected - 1);
            assert_eq!(original_capacity_to_repr(cap + 76), expected);
        } else if width == MIN_ORIGINAL_CAPACITY_WIDTH + 2 {
            assert_eq!(original_capacity_to_repr(cap - 1), expected - 1);
            assert_eq!(original_capacity_to_repr(cap - 48), expected - 1);
        }
    }
}

#[test]
fn test_original_capacity_from_repr() {
    assert_eq!(0, original_capacity_from_repr(0));

    let min_cap = 1 << MIN_ORIGINAL_CAPACITY_WIDTH;

    assert_eq!(min_cap, original_capacity_from_repr(1));
    assert_eq!(min_cap * 2, original_capacity_from_repr(2));
    assert_eq!(min_cap * 4, original_capacity_from_repr(3));
    assert_eq!(min_cap * 8, original_capacity_from_repr(4));
    assert_eq!(min_cap * 16, original_capacity_from_repr(5));
    assert_eq!(min_cap * 32, original_capacity_from_repr(6));
    assert_eq!(min_cap * 64, original_capacity_from_repr(7));
}
*/

unsafe impl Send for BytesMut {}
unsafe impl Sync for BytesMut {}

/*
 *
 * ===== PartialEq / PartialOrd =====
 *
 */

impl PartialEq<[u8]> for BytesMut {
    fn eq(&self, other: &[u8]) -> bool {
        &**self == other
    }
}

impl PartialOrd<[u8]> for BytesMut {
    fn partial_cmp(&self, other: &[u8]) -> Option<cmp::Ordering> {
        (**self).partial_cmp(other)
    }
}

impl PartialEq<BytesMut> for [u8] {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for [u8] {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        <[u8] as PartialOrd<[u8]>>::partial_cmp(self, other)
    }
}

impl PartialEq<str> for BytesMut {
    fn eq(&self, other: &str) -> bool {
        &**self == other.as_bytes()
    }
}

impl PartialOrd<str> for BytesMut {
    fn partial_cmp(&self, other: &str) -> Option<cmp::Ordering> {
        (**self).partial_cmp(other.as_bytes())
    }
}

impl PartialEq<BytesMut> for str {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for str {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        <[u8] as PartialOrd<[u8]>>::partial_cmp(self.as_bytes(), other)
    }
}

impl PartialEq<Vec<u8>> for BytesMut {
    fn eq(&self, other: &Vec<u8>) -> bool {
        *self == &other[..]
    }
}

impl PartialOrd<Vec<u8>> for BytesMut {
    fn partial_cmp(&self, other: &Vec<u8>) -> Option<cmp::Ordering> {
        (**self).partial_cmp(&other[..])
    }
}

impl PartialEq<BytesMut> for Vec<u8> {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for Vec<u8> {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        other.partial_cmp(self)
    }
}

impl PartialEq<String> for BytesMut {
    fn eq(&self, other: &String) -> bool {
        *self == &other[..]
    }
}

impl PartialOrd<String> for BytesMut {
    fn partial_cmp(&self, other: &String) -> Option<cmp::Ordering> {
        (**self).partial_cmp(other.as_bytes())
    }
}

impl PartialEq<BytesMut> for String {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for String {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        <[u8] as PartialOrd<[u8]>>::partial_cmp(self.as_bytes(), other)
    }
}

impl<'a, T: ?Sized> PartialEq<&'a T> for BytesMut
where
    BytesMut: PartialEq<T>,
{
    fn eq(&self, other: &&'a T) -> bool {
        *self == **other
    }
}

impl<'a, T: ?Sized> PartialOrd<&'a T> for BytesMut
where
    BytesMut: PartialOrd<T>,
{
    fn partial_cmp(&self, other: &&'a T) -> Option<cmp::Ordering> {
        self.partial_cmp(*other)
    }
}

impl PartialEq<BytesMut> for &[u8] {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for &[u8] {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        <[u8] as PartialOrd<[u8]>>::partial_cmp(self, other)
    }
}

impl PartialEq<BytesMut> for &str {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for &str {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        other.partial_cmp(self)
    }
}

impl PartialEq<BytesMut> for Bytes {
    fn eq(&self, other: &BytesMut) -> bool {
        &other[..] == &self[..]
    }
}

impl PartialEq<Bytes> for BytesMut {
    fn eq(&self, other: &Bytes) -> bool {
        &other[..] == &self[..]
    }
}

fn vptr(ptr: *mut u8) -> NonNull<u8> {
    if cfg!(debug_assertions) {
        NonNull::new(ptr).expect("Vec pointer should be non-null")
    } else {
        unsafe { NonNull::new_unchecked(ptr) }
    }
}

unsafe fn rebuild_vec(ptr: *mut u8, mut len: usize, mut cap: usize, off: usize) -> Vec<u8> {
    let ptr = ptr.offset(-(off as isize));
    len += off;
    cap += off;

    Vec::from_raw_parts(ptr, len, cap)
}

// ===== impl SharedVtable =====

static SHARED_VTABLE: Vtable = Vtable {
    clone: shared_v_clone,
    drop: shared_v_drop,
};

unsafe fn shared_v_clone(data: &AtomicPtr<()>, ptr: *const u8, len: usize) -> Bytes {
    let shared = data.load(Ordering::Relaxed) as *mut Shared;
    increment_shared(shared);

    let data = AtomicPtr::new(shared as _);
    Bytes::with_vtable(ptr, len, data, &SHARED_VTABLE)
}

unsafe fn shared_v_drop(data: &mut AtomicPtr<()>, _ptr: *const u8, _len: usize) {
    data.with_mut(|shared| {
        release_shared(*shared as *mut Shared);
    });
}

// compile-fails

/// ```compile_fail
/// use bytes::BytesMut;
/// #[deny(unused_must_use)]
/// {
///     let mut b1 = BytesMut::from("hello world");
///     b1.split_to(6);
/// }
/// ```
fn _split_to_must_use() {}

/// ```compile_fail
/// use bytes::BytesMut;
/// #[deny(unused_must_use)]
/// {
///     let mut b1 = BytesMut::from("hello world");
///     b1.split_off(6);
/// }
/// ```
fn _split_off_must_use() {}

/// ```compile_fail
/// use bytes::BytesMut;
/// #[deny(unused_must_use)]
/// {
///     let mut b1 = BytesMut::from("hello world");
///     b1.split();
/// }
/// ```
fn _split_must_use() {}

// fuzz tests
#[cfg(all(test, loom))]
mod fuzz {
    use loom::sync::Arc;
    use loom::thread;

    use super::BytesMut;
    use crate::Bytes;

    #[test]
    fn bytes_mut_cloning_frozen() {
        loom::model(|| {
            let a = BytesMut::from(&b"abcdefgh"[..]).split().freeze();
            let addr = a.as_ptr() as usize;

            // test the Bytes::clone is Sync by putting it in an Arc
            let a1 = Arc::new(a);
            let a2 = a1.clone();

            let t1 = thread::spawn(move || {
                let b: Bytes = (*a1).clone();
                assert_eq!(b.as_ptr() as usize, addr);
            });

            let t2 = thread::spawn(move || {
                let b: Bytes = (*a2).clone();
                assert_eq!(b.as_ptr() as usize, addr);
            });

            t1.join().unwrap();
            t2.join().unwrap();
        });
    }
}