inspect_format/
utils.rs

1// Copyright 2019 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use crate::constants;
6
7/// Returns the smallest order such that (MIN_ORDER_SHIFT << order) >= size.
8/// Size must be non zero.
9pub fn fit_order(size: usize) -> usize {
10    if size == 0 {
11        return 0;
12    }
13    // Safety: `leading_zeros` returns a u32, so this is safe promotion
14    (std::mem::size_of::<usize>() * 8 - (size - 1).leading_zeros() as usize)
15        .saturating_sub(constants::MIN_ORDER_SHIFT)
16}
17
18/// Get size in bytes of a given |order|.
19pub fn order_to_size(order: u8) -> usize {
20    constants::MIN_ORDER_SIZE << order
21}
22
23/// Get the necessary |block size| to fit the given |payload_size| in range
24/// MIN_ORDER_SIZE <= block size <= MAX_ORDER_SIZE
25pub fn block_size_for_payload(payload_size: usize) -> usize {
26    (payload_size + constants::HEADER_SIZE_BYTES)
27        .clamp(constants::MIN_ORDER_SIZE, constants::MAX_ORDER_SIZE)
28}
29
30/// Get the size in bytes for the payload section of a block of the given |order|.
31pub fn payload_size_for_order(order: u8) -> usize {
32    order_to_size(order) - constants::HEADER_SIZE_BYTES
33}
34
35#[cfg(test)]
36mod test {
37    use super::*;
38
39    #[test]
40    fn fit_order_test() {
41        assert_eq!(0, fit_order(1));
42        assert_eq!(0, fit_order(16));
43        assert_eq!(1, fit_order(17));
44        assert_eq!(2, fit_order(33));
45        assert_eq!(7, fit_order(2048));
46    }
47
48    #[test]
49    fn order_to_size_test() {
50        assert_eq!(16, order_to_size(0));
51        assert_eq!(32, order_to_size(1));
52        assert_eq!(64, order_to_size(2));
53        assert_eq!(128, order_to_size(3));
54        assert_eq!(256, order_to_size(4));
55        assert_eq!(512, order_to_size(5));
56        assert_eq!(1024, order_to_size(6));
57        assert_eq!(2048, order_to_size(7));
58    }
59
60    #[test]
61    fn fit_payload_test() {
62        for payload_size in 0..500 {
63            let block_size = block_size_for_payload(payload_size);
64            let order = fit_order(block_size) as u8;
65            let payload_max = payload_size_for_order(order);
66            assert!(
67                payload_size <= payload_max,
68                "Needed {payload_size} bytes for a payload, but only got {payload_max}; block size {block_size}, order {order}"
69            );
70        }
71    }
72}
inspect_format/utils.rs

inspect_format/
utils.rs
