itoa/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)
//!
//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
//! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
//!
//! <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.
//!
//! [libcore]: https://github.com/rust-lang/rust/blob/b8214dc6c6fc20d0a660fb5700dca9ebf51ebe89/src/libcore/fmt/num.rs#L201-L254
//! [`core::fmt::Formatter`]: https://doc.rust-lang.org/std/fmt/struct.Formatter.html
//! [`ryu`]: https://github.com/dtolnay/ryu
//!
//! # 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/1.0.12")]
#![no_std]
#![allow(
clippy::cast_lossless,
clippy::cast_possible_truncation,
clippy::cast_possible_wrap,
clippy::cast_sign_loss,
clippy::expl_impl_clone_on_copy,
clippy::must_use_candidate,
clippy::needless_doctest_main,
clippy::unreadable_literal
)]
mod udiv128;
use core::hint;
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 Copy for Buffer {}
impl Clone for Buffer {
#[inline]
#[allow(clippy::non_canonical_clone_impl)] // false positive https://github.com/rust-lang/rust-clippy/issues/11072
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 {
let string = i.write(unsafe {
&mut *(&mut self.bytes as *mut [MaybeUninit<u8>; I128_MAX_LEN]
as *mut <I as private::Sealed>::Buffer)
});
if string.len() > I::MAX_STR_LEN {
unsafe { hint::unreachable_unchecked() };
}
string
}
}
/// 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 {
/// The maximum length of string that formatting an integer of this type can
/// produce on the current target platform.
const MAX_STR_LEN: usize;
}
// 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;
}
}
static DEC_DIGITS_LUT: [u8; 200] = *b"\
0001020304050607080910111213141516171819\
2021222324252627282930313233343536373839\
4041424344454647484950515253545556575859\
6061626364656667686970717273747576777879\
8081828384858687888990919293949596979899";
// Adaptation of the original implementation at
// https://github.com/rust-lang/rust/blob/b8214dc6c6fc20d0a660fb5700dca9ebf51ebe89/src/libcore/fmt/num.rs#L188-L266
macro_rules! impl_Integer {
($($t:ty[$max_len:expr])* as $large_unsigned:ty) => {$(
impl Integer for $t {
const MAX_STR_LEN: usize = $max_len;
}
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 $large_unsigned
} else {
// Convert negative number to positive by summing 1 to its two's complement.
(!(self as $large_unsigned)).wrapping_add(1)
};
let mut curr = buf.len() as isize;
let buf_ptr = buf.as_mut_ptr() as *mut u8;
let lut_ptr = DEC_DIGITS_LUT.as_ptr();
// Need at least 16 bits for the 4-digits-at-a-time to work.
if mem::size_of::<$t>() >= 2 {
// Eagerly decode 4 digits 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;
unsafe {
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 digits long.
let mut n = n as isize; // Possibly reduce 64-bit math.
// Decode 2 more digits, if >2 digits.
if n >= 100 {
let d1 = (n % 100) << 1;
n /= 100;
curr -= 2;
unsafe {
ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
}
}
// Decode last 1 or 2 digits.
if n < 10 {
curr -= 1;
unsafe {
*buf_ptr.offset(curr) = (n as u8) + b'0';
}
} else {
let d1 = n << 1;
curr -= 2;
unsafe {
ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
}
}
if !is_nonnegative {
curr -= 1;
unsafe {
*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[I8_MAX_LEN]
u8[U8_MAX_LEN]
i16[I16_MAX_LEN]
u16[U16_MAX_LEN]
i32[I32_MAX_LEN]
u32[U32_MAX_LEN]
as u32
}
impl_Integer!(i64[I64_MAX_LEN] u64[U64_MAX_LEN] as u64);
#[cfg(target_pointer_width = "16")]
impl_Integer!(isize[I16_MAX_LEN] usize[U16_MAX_LEN] as u16);
#[cfg(target_pointer_width = "32")]
impl_Integer!(isize[I32_MAX_LEN] usize[U32_MAX_LEN] as u32);
#[cfg(target_pointer_width = "64")]
impl_Integer!(isize[I64_MAX_LEN] usize[U64_MAX_LEN] as u64);
macro_rules! impl_Integer128 {
($($t:ty[$max_len:expr])*) => {$(
impl Integer for $t {
const MAX_STR_LEN: usize = $max_len;
}
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 negative number to positive by summing 1 to its two's complement.
(!(self as u128)).wrapping_add(1)
};
let mut curr = buf.len() as isize;
let buf_ptr = buf.as_mut_ptr() as *mut u8;
// Divide by 10^19 which is the highest power less than 2^64.
let (n, rem) = udiv128::udivmod_1e19(n);
let buf1 = unsafe { buf_ptr.offset(curr - U64_MAX_LEN as isize) as *mut [MaybeUninit<u8>; U64_MAX_LEN] };
curr -= rem.write(unsafe { &mut *buf1 }).len() as isize;
if n != 0 {
// Memset the base10 leading zeros of rem.
let target = buf.len() as isize - 19;
unsafe {
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 = unsafe { buf_ptr.offset(curr - U64_MAX_LEN as isize) as *mut [MaybeUninit<u8>; U64_MAX_LEN] };
curr -= rem.write(unsafe { &mut *buf2 }).len() as isize;
if n != 0 {
// Memset the leading zeros.
let target = buf.len() as isize - 38;
unsafe {
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;
unsafe {
*buf_ptr.offset(curr) = (n as u8) + b'0';
}
}
}
if !is_nonnegative {
curr -= 1;
unsafe {
*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 U128_MAX_LEN: usize = 39;
const I128_MAX_LEN: usize = 40;
impl_Integer128!(i128[I128_MAX_LEN] u128[U128_MAX_LEN]);