numtoa/lib.rs
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//! The standard library provides a convenient method of converting numbers into strings, but these strings are
//! heap-allocated. If you have an application which needs to convert large volumes of numbers into strings, but don't
//! want to pay the price of heap allocation, this crate provides an efficient `no_std`-compatible method of heaplessly converting numbers
//! into their string representations, storing the representation within a reusable byte array.
//!
//! In addition to supporting the standard base 10 conversion, this implementation allows you to select the base of
//! your choice. Therefore, if you want a binary representation, set the base to 2. If you want hexadecimal, set the
//! base to 16.
//!
//! # Convenience Example
//!
//! ```
//! use numtoa::NumToA;
//!
//! let mut buf = [0u8; 20];
//! let mut string = String::new();
//!
//! for number in (1..10) {
//! string.push_str(number.numtoa_str(10, &mut buf));
//! string.push('\n');
//! }
//!
//! println!("{}", string);
//! ```
//!
//! ## Base 10 Example
//! ```
//! use numtoa::NumToA;
//! use std::io::{self, Write};
//!
//! let stdout = io::stdout();
//! let mut stdout = stdout.lock();
//! let mut buffer = [0u8; 20];
//!
//! let number: u32 = 162392;
//! let mut start_indice = number.numtoa(10, &mut buffer);
//! let _ = stdout.write(&buffer[start_indice..]);
//! let _ = stdout.write(b"\n");
//! assert_eq!(&buffer[start_indice..], b"162392");
//!
//! let other_number: i32 = -6235;
//! start_indice = other_number.numtoa(10, &mut buffer);
//! let _ = stdout.write(&buffer[start_indice..]);
//! let _ = stdout.write(b"\n");
//! assert_eq!(&buffer[start_indice..], b"-6235");
//!
//! let other_number: i8 = -128;
//! start_indice = other_number.numtoa(10, &mut buffer);
//! let _ = stdout.write(&buffer[start_indice..]);
//! let _ = stdout.write(b"\n");
//! assert_eq!(&buffer[start_indice..], b"-128");
//!
//! let other_number: i8 = 53;
//! start_indice = other_number.numtoa(10, &mut buffer);
//! let _ = stdout.write(&buffer[start_indice..]);
//! let _ = stdout.write(b"\n");
//! assert_eq!(&buffer[start_indice..], b"53");
//!
//! let other_number: i16 = -256;
//! start_indice = other_number.numtoa(10, &mut buffer);
//! let _ = stdout.write(&buffer[start_indice..]);
//! let _ = stdout.write(b"\n");
//! assert_eq!(&buffer[start_indice..], b"-256");
//!
//! let other_number: i16 = -32768;
//! start_indice = other_number.numtoa(10, &mut buffer);
//! let _ = stdout.write(&buffer[start_indice..]);
//! let _ = stdout.write(b"\n");
//! assert_eq!(&buffer[start_indice..], b"-32768");
//!
//! let large_num: u64 = 35320842;
//! start_indice = large_num.numtoa(10, &mut buffer);
//! let _ = stdout.write(&buffer[start_indice..]);
//! let _ = stdout.write(b"\n");
//! assert_eq!(&buffer[start_indice..], b"35320842");
//!
//! let max_u64: u64 = 18446744073709551615;
//! start_indice = max_u64.numtoa(10, &mut buffer);
//! let _ = stdout.write(&buffer[start_indice..]);
//! let _ = stdout.write(b"\n");
//! assert_eq!(&buffer[start_indice..], b"18446744073709551615");
//! ```
#![no_std]
use core::mem::size_of;
#[cfg(feature = "std")]
extern crate std;
#[cfg(feature = "std")]
use std::str;
/// Converts a number into a string representation, storing the conversion into a mutable byte slice.
pub trait NumToA<T> {
/// Given a base for encoding and a mutable byte slice, write the number into the byte slice and return the
/// indice where the inner string begins. The inner string can be extracted by slicing the byte slice from
/// that indice.
///
/// # Panics
/// If the supplied buffer is smaller than the number of bytes needed to write the integer, this will panic.
/// On debug builds, this function will perform a check on base 10 conversions to ensure that the input array
/// is large enough to hold the largest possible value in digits.
///
/// # Example
/// ```
/// use numtoa::NumToA;
/// use std::io::{self, Write};
///
/// let stdout = io::stdout();
/// let stdout = &mut io::stdout();
///
/// let mut buffer = [0u8; 20];
/// let number = 15325;
/// let start_indice = number.numtoa(10, &mut buffer);
/// let _ = stdout.write(&buffer[start_indice..]);
/// assert_eq!(&buffer[start_indice..], b"15325");
/// ```
fn numtoa(self, base: T, string: &mut [u8]) -> usize;
#[cfg(feature = "std")]
/// Convenience method for quickly getting a string from the input's array buffer.
fn numtoa_str(self, base: T, buf: &mut [u8; 20]) -> &str;
}
// A lookup table to prevent the need for conditional branching
// The value of the remainder of each step will be used as the index
const LOOKUP: &[u8] = b"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
// A lookup table optimized for decimal lookups. Each two indices represents one possible number.
const DEC_LOOKUP: &[u8; 200] = b"0001020304050607080910111213141516171819\
2021222324252627282930313233343536373839\
4041424344454647484950515253545556575859\
6061626364656667686970717273747576777879\
8081828384858687888990919293949596979899";
macro_rules! base_10 {
($number:ident, $index:ident, $string:ident) => {
// Decode four characters at the same time
while $number > 9999 {
let rem = ($number % 10000) as u16;
let (frst, scnd) = ((rem / 100) * 2, (rem % 100) * 2);
$string[$index-3..$index-1].copy_from_slice(&DEC_LOOKUP[frst as usize..frst as usize+2]);
$string[$index-1..$index+1].copy_from_slice(&DEC_LOOKUP[scnd as usize..scnd as usize+2]);
$index = $index.wrapping_sub(4);
$number /= 10000;
}
if $number > 999 {
let (frst, scnd) = (($number / 100) * 2, ($number % 100) * 2);
$string[$index-3..$index-1].copy_from_slice(&DEC_LOOKUP[frst as usize..frst as usize+2]);
$string[$index-1..$index+1].copy_from_slice(&DEC_LOOKUP[scnd as usize..scnd as usize+2]);
$index = $index.wrapping_sub(4);
} else if $number > 99 {
let section = ($number as u16 / 10) * 2;
$string[$index-2..$index].copy_from_slice(&DEC_LOOKUP[section as usize..section as usize+2]);
$string[$index] = LOOKUP[($number % 10) as usize];
$index = $index.wrapping_sub(3);
} else if $number > 9 {
$number *= 2;
$string[$index-1..$index+1].copy_from_slice(&DEC_LOOKUP[$number as usize..$number as usize+2]);
$index = $index.wrapping_sub(2);
} else {
$string[$index] = LOOKUP[$number as usize];
$index = $index.wrapping_sub(1);
}
}
}
macro_rules! impl_unsized_numtoa_for {
($t:ty) => {
impl NumToA<$t> for $t {
fn numtoa(mut self, base: $t, string: &mut [u8]) -> usize {
// Check if the buffer is large enough and panic on debug builds if it isn't
if cfg!(debug_assertions) {
if base == 10 {
match size_of::<$t>() {
2 => debug_assert!(string.len() >= 5, "u16 base 10 conversions require at least 5 bytes"),
4 => debug_assert!(string.len() >= 10, "u32 base 10 conversions require at least 10 bytes"),
8 => debug_assert!(string.len() >= 20, "u64 base 10 conversions require at least 20 bytes"),
_ => unreachable!()
}
}
}
let mut index = string.len() - 1;
if self == 0 {
string[index] = b'0';
return index;
}
if base == 10 {
// Convert using optimized base 10 algorithm
base_10!(self, index, string);
} else {
while self != 0 {
let rem = self % base;
string[index] = LOOKUP[rem as usize];
index = index.wrapping_sub(1);
self /= base;
}
}
index.wrapping_add(1)
}
#[cfg(feature = "std")]
fn numtoa_str(self, base: $t, buf: &mut [u8; 20]) -> &str {
let s = self.numtoa(base, buf);
unsafe { str::from_utf8_unchecked(&buf[s..]) }
}
}
}
}
macro_rules! impl_sized_numtoa_for {
($t:ty) => {
impl NumToA<$t> for $t {
fn numtoa(mut self, base: $t, string: &mut [u8]) -> usize {
if cfg!(debug_assertions) {
if base == 10 {
match size_of::<$t>() {
2 => debug_assert!(string.len() >= 6, "i16 base 10 conversions require at least 6 bytes"),
4 => debug_assert!(string.len() >= 11, "i32 base 10 conversions require at least 11 bytes"),
8 => debug_assert!(string.len() >= 20, "i64 base 10 conversions require at least 20 bytes"),
_ => unreachable!()
}
}
}
let mut index = string.len() - 1;
let mut is_negative = false;
if self < 0 {
is_negative = true;
self = match self.checked_abs() {
Some(value) => value,
None => {
let value = <$t>::max_value();
string[index] = LOOKUP[((value % base + 1) % base) as usize];
index -= 1;
value / base + ((value % base == base - 1) as $t)
}
};
} else if self == 0 {
string[index] = b'0';
return index;
}
if base == 10 {
// Convert using optimized base 10 algorithm
base_10!(self, index, string);
} else {
while self != 0 {
let rem = self % base;
string[index] = LOOKUP[rem as usize];
index = index.wrapping_sub(1);
self /= base;
}
}
if is_negative {
string[index] = b'-';
index = index.wrapping_sub(1);
}
index.wrapping_add(1)
}
#[cfg(feature = "std")]
fn numtoa_str(self, base: $t, buf: &mut [u8; 20]) -> &str {
let s = self.numtoa(base, buf);
unsafe { str::from_utf8_unchecked(&buf[s..]) }
}
}
}
}
impl_sized_numtoa_for!(i16);
impl_sized_numtoa_for!(i32);
impl_sized_numtoa_for!(i64);
impl_sized_numtoa_for!(isize);
impl_unsized_numtoa_for!(u16);
impl_unsized_numtoa_for!(u32);
impl_unsized_numtoa_for!(u64);
impl_unsized_numtoa_for!(usize);
impl NumToA<i8> for i8 {
fn numtoa(mut self, base: i8, string: &mut [u8]) -> usize {
if cfg!(debug_assertions) {
if base == 10 {
debug_assert!(string.len() >= 4, "i8 conversions need at least 4 bytes");
}
}
let mut index = string.len() - 1;
let mut is_negative = false;
if self < 0 {
is_negative = true;
self = match self.checked_abs() {
Some(value) => value,
None => {
let value = <i8>::max_value();
string[index] = LOOKUP[((value % base + 1) % base) as usize];
index -= 1;
value / base + ((value % base == base - 1) as i8)
}
};
} else if self == 0 {
string[index] = b'0';
return index;
}
if base == 10 {
if self > 99 {
let section = (self / 10) * 2;
string[index-2..index].copy_from_slice(&DEC_LOOKUP[section as usize..section as usize+2]);
string[index] = LOOKUP[(self % 10) as usize];
index = index.wrapping_sub(3);
} else if self > 9 {
self *= 2;
string[index-1..index+1].copy_from_slice(&DEC_LOOKUP[self as usize..self as usize+2]);
index = index.wrapping_sub(2);
} else {
string[index] = LOOKUP[self as usize];
index = index.wrapping_sub(1);
}
} else {
while self != 0 {
let rem = self % base;
string[index] = LOOKUP[rem as usize];
index = index.wrapping_sub(1);
self /= base;
}
}
if is_negative {
string[index] = b'-';
index = index.wrapping_sub(1);
}
index.wrapping_add(1)
}
#[cfg(feature = "std")]
fn numtoa_str(self, base: Self, buf: &mut [u8; 20]) -> &str {
let s = self.numtoa(base, buf);
unsafe { str::from_utf8_unchecked(&buf[s..]) }
}
}
impl NumToA<u8> for u8 {
fn numtoa(mut self, base: u8, string: &mut [u8]) -> usize {
if cfg!(debug_assertions) {
if base == 10 {
debug_assert!(string.len() >= 3, "u8 conversions need at least 3 bytes");
}
}
let mut index = string.len() - 1;
if self == 0 {
string[index] = b'0';
return index;
}
if base == 10 {
if self > 99 {
let section = (self / 10) * 2;
string[index-2..index].copy_from_slice(&DEC_LOOKUP[section as usize..section as usize+2]);
string[index] = LOOKUP[(self % 10) as usize];
index = index.wrapping_sub(3);
} else if self > 9 {
self *= 2;
string[index-1..index+1].copy_from_slice(&DEC_LOOKUP[self as usize..self as usize+2]);
index = index.wrapping_sub(2);
} else {
string[index] = LOOKUP[self as usize];
index = index.wrapping_sub(1);
}
} else {
while self != 0 {
let rem = self % base;
string[index] = LOOKUP[rem as usize];
index = index.wrapping_sub(1);
self /= base;
}
}
index.wrapping_add(1)
}
#[cfg(feature = "std")]
fn numtoa_str(self, base: Self, buf: &mut [u8; 20]) -> &str {
let s = self.numtoa(base, buf);
unsafe { str::from_utf8_unchecked(&buf[s..]) }
}
}
#[test]
fn str_convenience() {
let mut buffer = [0u8; 20];
assert_eq!("256123", 256123.numtoa_str(10, &mut buffer));
}
#[test]
#[should_panic]
fn base10_u8_array_too_small() {
let mut buffer = [0u8; 2];
let _ = 0u8.numtoa(10, &mut buffer);
}
#[test]
fn base10_u8_array_just_right() {
let mut buffer = [0u8; 3];
let _ = 0u8.numtoa(10, &mut buffer);
}
#[test]
#[should_panic]
fn base10_i8_array_too_small() {
let mut buffer = [0u8; 3];
let _ = 0i8.numtoa(10, &mut buffer);
}
#[test]
fn base10_i8_array_just_right() {
let mut buffer = [0u8; 4];
let i = (-127i8).numtoa(10, &mut buffer);
assert_eq!(&buffer[i..], b"-127");
}
#[test]
#[should_panic]
fn base10_i16_array_too_small() {
let mut buffer = [0u8; 5];
let _ = 0i16.numtoa(10, &mut buffer);
}
#[test]
fn base10_i16_array_just_right() {
let mut buffer = [0u8; 6];
let i = (-12768i16).numtoa(10, &mut buffer);
assert_eq!(&buffer[i..], b"-12768");
}
#[test]
#[should_panic]
fn base10_u16_array_too_small() {
let mut buffer = [0u8; 4];
let _ = 0u16.numtoa(10, &mut buffer);
}
#[test]
fn base10_u16_array_just_right() {
let mut buffer = [0u8; 5];
let _ = 0u16.numtoa(10, &mut buffer);
}
#[test]
#[should_panic]
fn base10_i32_array_too_small() {
let mut buffer = [0u8; 10];
let _ = 0i32.numtoa(10, &mut buffer);
}
#[test]
fn base10_i32_array_just_right() {
let mut buffer = [0u8; 11];
let _ = 0i32.numtoa(10, &mut buffer);
}
#[test]
#[should_panic]
fn base10_u32_array_too_small() {
let mut buffer = [0u8; 9];
let _ = 0u32.numtoa(10, &mut buffer);
}
#[test]
fn base10_u32_array_just_right() {
let mut buffer = [0u8; 10];
let _ = 0u32.numtoa(10, &mut buffer);
}
#[test]
#[should_panic]
fn base10_i64_array_too_small() {
let mut buffer = [0u8; 19];
let _ = 0i64.numtoa(10, &mut buffer);
}
#[test]
fn base10_i64_array_just_right() {
let mut buffer = [0u8; 20];
let _ = 0i64.numtoa(10, &mut buffer);
}
#[test]
#[should_panic]
fn base10_u64_array_too_small() {
let mut buffer = [0u8; 19];
let _ = 0u64.numtoa(10, &mut buffer);
}
#[test]
fn base10_u64_array_just_right() {
let mut buffer = [0u8; 20];
let _ = 0u64.numtoa(10, &mut buffer);
}
#[test]
fn base8_min_signed_number() {
let mut buffer = [0u8; 30];
let i = (-128i8).numtoa(8, &mut buffer);
assert_eq!(&buffer[i..], b"-200");
let i = (-32768i16).numtoa(8, &mut buffer);
assert_eq!(&buffer[i..], b"-100000");
let i = (-2147483648i32).numtoa(8, &mut buffer);
assert_eq!(&buffer[i..], b"-20000000000");
let i = (-9223372036854775808i64).numtoa(8, &mut buffer);
assert_eq!(&buffer[i..], b"-1000000000000000000000");
}
#[test]
fn base16_min_signed_number() {
let mut buffer = [0u8; 20];
let i = (-128i8).numtoa(16, &mut buffer);
assert_eq!(&buffer[i..], b"-80");
let i = (-32768i16).numtoa(16, &mut buffer);
assert_eq!(&buffer[i..], b"-8000");
let i = (-2147483648i32).numtoa(16, &mut buffer);
assert_eq!(&buffer[i..], b"-80000000");
let i = (-9223372036854775808i64).numtoa(16, &mut buffer);
assert_eq!(&buffer[i..], b"-8000000000000000");
}