mozilla-central/third_party/rust/itoa/src/lib.rs

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//! [![github]](https://github.com/dtolnay/itoa) [![crates-io]](https://crates.io/crates/itoa) [![docs-rs]](https://docs.rs/itoa)
//!
//!
//! <br>
//!
//! This crate provides a fast conversion of integer primitives to decimal
//! strings. The implementation comes straight from [libcore] but avoids the
//! performance penalty of going through [`core::fmt::Formatter`].
//!
//! See also [`ryu`] for printing floating point primitives.
//!
//!
//! # Example
//!
//! ```
//! fn main() {
//! let mut buffer = itoa::Buffer::new();
//! let printed = buffer.format(128u64);
//! assert_eq!(printed, "128");
//! }
//! ```
//!
//! # Performance (lower is better)
//!
#![doc(html_root_url = "https://docs.rs/itoa/1.0.5")]
#![no_std]
#![allow(
clippy::cast_lossless,
clippy::cast_possible_truncation,
clippy::must_use_candidate,
clippy::unreadable_literal
)]
mod udiv128;
use core::mem::{self, MaybeUninit};
use core::{ptr, slice, str};
#[cfg(feature = "no-panic")]
use no_panic::no_panic;
/// A correctly sized stack allocation for the formatted integer to be written
/// into.
///
/// # Example
///
/// ```
/// let mut buffer = itoa::Buffer::new();
/// let printed = buffer.format(1234);
/// assert_eq!(printed, "1234");
/// ```
pub struct Buffer {
bytes: [MaybeUninit<u8>; I128_MAX_LEN],
}
impl Default for Buffer {
#[inline]
fn default() -> Buffer {
Buffer::new()
}
}
impl Clone for Buffer {
#[inline]
fn clone(&self) -> Self {
Buffer::new()
}
}
impl Buffer {
/// This is a cheap operation; you don't need to worry about reusing buffers
/// for efficiency.
#[inline]
#[cfg_attr(feature = "no-panic", no_panic)]
pub fn new() -> Buffer {
let bytes = [MaybeUninit::<u8>::uninit(); I128_MAX_LEN];
Buffer { bytes }
}
/// Print an integer into this buffer and return a reference to its string
/// representation within the buffer.
#[cfg_attr(feature = "no-panic", no_panic)]
pub fn format<I: Integer>(&mut self, i: I) -> &str {
i.write(unsafe {
&mut *(&mut self.bytes as *mut [MaybeUninit<u8>; I128_MAX_LEN]
as *mut <I as private::Sealed>::Buffer)
})
}
}
/// An integer that can be written into an [`itoa::Buffer`][Buffer].
///
/// This trait is sealed and cannot be implemented for types outside of itoa.
pub trait Integer: private::Sealed {}
// Seal to prevent downstream implementations of the Integer trait.
mod private {
pub trait Sealed: Copy {
type Buffer: 'static;
fn write(self, buf: &mut Self::Buffer) -> &str;
}
}
const DEC_DIGITS_LUT: &[u8] = b"\
0001020304050607080910111213141516171819\
2021222324252627282930313233343536373839\
4041424344454647484950515253545556575859\
6061626364656667686970717273747576777879\
8081828384858687888990919293949596979899";
// Adaptation of the original implementation at
macro_rules! impl_Integer {
($($max_len:expr => $t:ident),* as $conv_fn:ident) => {$(
impl Integer for $t {}
impl private::Sealed for $t {
type Buffer = [MaybeUninit<u8>; $max_len];
#[allow(unused_comparisons)]
#[inline]
#[cfg_attr(feature = "no-panic", no_panic)]
fn write(self, buf: &mut [MaybeUninit<u8>; $max_len]) -> &str {
let is_nonnegative = self >= 0;
let mut n = if is_nonnegative {
self as $conv_fn
} else {
// convert the negative num to positive by summing 1 to it's 2 complement
(!(self as $conv_fn)).wrapping_add(1)
};
let mut curr = buf.len() as isize;
let buf_ptr = buf.as_mut_ptr() as *mut u8;
let lut_ptr = DEC_DIGITS_LUT.as_ptr();
unsafe {
// need at least 16 bits for the 4-characters-at-a-time to work.
if mem::size_of::<$t>() >= 2 {
// eagerly decode 4 characters at a time
while n >= 10000 {
let rem = (n % 10000) as isize;
n /= 10000;
let d1 = (rem / 100) << 1;
let d2 = (rem % 100) << 1;
curr -= 4;
ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
ptr::copy_nonoverlapping(lut_ptr.offset(d2), buf_ptr.offset(curr + 2), 2);
}
}
// if we reach here numbers are <= 9999, so at most 4 chars long
let mut n = n as isize; // possibly reduce 64bit math
// decode 2 more chars, if > 2 chars
if n >= 100 {
let d1 = (n % 100) << 1;
n /= 100;
curr -= 2;
ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
}
// decode last 1 or 2 chars
if n < 10 {
curr -= 1;
*buf_ptr.offset(curr) = (n as u8) + b'0';
} else {
let d1 = n << 1;
curr -= 2;
ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
}
if !is_nonnegative {
curr -= 1;
*buf_ptr.offset(curr) = b'-';
}
}
let len = buf.len() - curr as usize;
let bytes = unsafe { slice::from_raw_parts(buf_ptr.offset(curr), len) };
unsafe { str::from_utf8_unchecked(bytes) }
}
}
)*};
}
const I8_MAX_LEN: usize = 4;
const U8_MAX_LEN: usize = 3;
const I16_MAX_LEN: usize = 6;
const U16_MAX_LEN: usize = 5;
const I32_MAX_LEN: usize = 11;
const U32_MAX_LEN: usize = 10;
const I64_MAX_LEN: usize = 20;
const U64_MAX_LEN: usize = 20;
impl_Integer!(
I8_MAX_LEN => i8,
U8_MAX_LEN => u8,
I16_MAX_LEN => i16,
U16_MAX_LEN => u16,
I32_MAX_LEN => i32,
U32_MAX_LEN => u32
as u32);
impl_Integer!(I64_MAX_LEN => i64, U64_MAX_LEN => u64 as u64);
#[cfg(target_pointer_width = "16")]
impl_Integer!(I16_MAX_LEN => isize, U16_MAX_LEN => usize as u16);
#[cfg(target_pointer_width = "32")]
impl_Integer!(I32_MAX_LEN => isize, U32_MAX_LEN => usize as u32);
#[cfg(target_pointer_width = "64")]
impl_Integer!(I64_MAX_LEN => isize, U64_MAX_LEN => usize as u64);
macro_rules! impl_Integer128 {
($($max_len:expr => $t:ident),*) => {$(
impl Integer for $t {}
impl private::Sealed for $t {
type Buffer = [MaybeUninit<u8>; $max_len];
#[allow(unused_comparisons)]
#[inline]
#[cfg_attr(feature = "no-panic", no_panic)]
fn write(self, buf: &mut [MaybeUninit<u8>; $max_len]) -> &str {
let is_nonnegative = self >= 0;
let n = if is_nonnegative {
self as u128
} else {
// convert the negative num to positive by summing 1 to it's 2 complement
(!(self as u128)).wrapping_add(1)
};
let mut curr = buf.len() as isize;
let buf_ptr = buf.as_mut_ptr() as *mut u8;
unsafe {
// Divide by 10^19 which is the highest power less than 2^64.
let (n, rem) = udiv128::udivmod_1e19(n);
let buf1 = buf_ptr.offset(curr - U64_MAX_LEN as isize) as *mut [MaybeUninit<u8>; U64_MAX_LEN];
curr -= rem.write(&mut *buf1).len() as isize;
if n != 0 {
// Memset the base10 leading zeros of rem.
let target = buf.len() as isize - 19;
ptr::write_bytes(buf_ptr.offset(target), b'0', (curr - target) as usize);
curr = target;
// Divide by 10^19 again.
let (n, rem) = udiv128::udivmod_1e19(n);
let buf2 = buf_ptr.offset(curr - U64_MAX_LEN as isize) as *mut [MaybeUninit<u8>; U64_MAX_LEN];
curr -= rem.write(&mut *buf2).len() as isize;
if n != 0 {
// Memset the leading zeros.
let target = buf.len() as isize - 38;
ptr::write_bytes(buf_ptr.offset(target), b'0', (curr - target) as usize);
curr = target;
// There is at most one digit left
// because u128::max / 10^19 / 10^19 is 3.
curr -= 1;
*buf_ptr.offset(curr) = (n as u8) + b'0';
}
}
if !is_nonnegative {
curr -= 1;
*buf_ptr.offset(curr) = b'-';
}
let len = buf.len() - curr as usize;
let bytes = slice::from_raw_parts(buf_ptr.offset(curr), len);
str::from_utf8_unchecked(bytes)
}
}
}
)*};
}
const U128_MAX_LEN: usize = 39;
const I128_MAX_LEN: usize = 40;
impl_Integer128!(I128_MAX_LEN => i128, U128_MAX_LEN => u128);