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perf: more optimized itoa (#203)
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* crazily optimize `itoa`

* restore `to_string` to bench targets
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@kanarus
kanarus committed Jul 5, 2024
1 parent 4485100 commit 1659eba
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Showing 2 changed files with 463 additions and 29 deletions.
343 changes: 339 additions & 4 deletions benches/benches/itoa.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,14 +2,344 @@


mod candiate {#![allow(unused)]
#[inline(always)]
pub fn itoa_lib(n: usize) -> String {
ohkami_lib::num::itoa(n)
}

#[inline(always)]
pub fn to_string(n: usize) -> String {
n.to_string()
}

#[inline(always)]
pub fn itoa(mut n: usize) -> String {
ohkami_lib::num::itoa(n)
pub fn itoa_01(mut n: usize) -> String {
let log10 = match usize::checked_ilog10(n) {
Some(log10) => log10 as usize,
None => return String::from("0")
};
let len = 1 + log10;
let mut digits = vec![0u8; len];
{
for i in 0..log10 {
let d = 10_usize.pow((log10 - i) as u32);
let (div, rem) = (n / d, n % d);
*unsafe {digits.get_unchecked_mut(i as usize)} = b'0' + div as u8;
n = rem;
}
*unsafe {digits.get_unchecked_mut(log10)} = b'0' + n as u8;
}
unsafe {String::from_utf8_unchecked(digits)}
}

#[inline(always)]
pub fn itoa_02(mut n: usize) -> String {
let log10 = match usize::checked_ilog10(n) {
Some(log10) => log10 as usize,
None => return String::from("0")
};
let mut digits = vec![b'0'; 1 + log10];
{
for i in 0..log10 {
let d = 10_usize.pow((log10 - i) as u32);
let q = n / d;
*unsafe {digits.get_unchecked_mut(i as usize)} += q as u8;
n -= d * q;
}
*unsafe {digits.get_unchecked_mut(log10)} += n as u8;
}
unsafe {String::from_utf8_unchecked(digits)}
}

#[inline(always)]
pub fn itoa_03(mut n: usize) -> String {
const MAX: usize = usize::ilog10(usize::MAX) as _;

const DIGITS: [usize; MAX+1] = [
10_usize.pow(MAX as u32-0),
10_usize.pow(MAX as u32-1),
10_usize.pow(MAX as u32-2),
10_usize.pow(MAX as u32-3),
10_usize.pow(MAX as u32-4),
10_usize.pow(MAX as u32-5),
10_usize.pow(MAX as u32-6),
10_usize.pow(MAX as u32-7),
10_usize.pow(MAX as u32-8),
10_usize.pow(MAX as u32-9),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-10),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-11),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-12),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-13),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-14),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-15),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-16),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-17),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-18),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-19),
];

let log10 = match usize::checked_ilog10(n) {
Some(log10) => log10 as usize,
None => return String::from("0")
};
let mut digits = vec![b'0'; 1 + log10];
{
for i in 0..log10 {
let d = *unsafe {DIGITS.get_unchecked(i)};
let q = n / d;
*unsafe {digits.get_unchecked_mut(i as usize)} += q as u8;
n -= d * q;
}
*unsafe {digits.get_unchecked_mut(log10)} += n as u8;
}
unsafe {String::from_utf8_unchecked(digits)}
}

#[inline(always)]
pub fn itoa_04(mut n: usize) -> String {
const MAX: usize = usize::ilog10(usize::MAX) as _;

const DIGITS: [usize; MAX+1] = [
10_usize.pow(MAX as u32-0),
10_usize.pow(MAX as u32-1),
10_usize.pow(MAX as u32-2),
10_usize.pow(MAX as u32-3),
10_usize.pow(MAX as u32-4),
10_usize.pow(MAX as u32-5),
10_usize.pow(MAX as u32-6),
10_usize.pow(MAX as u32-7),
10_usize.pow(MAX as u32-8),
10_usize.pow(MAX as u32-9),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-10),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-11),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-12),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-13),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-14),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-15),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-16),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-17),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-18),
#[cfg(target_pointer_width="64")] 10_usize.pow(MAX as u32-19),
];

let mut digits = [b'0'; DIGITS.len()];
let mut len = 0; loop {
let d = *unsafe {DIGITS.get_unchecked(len)};
let q = n / d;
*unsafe {digits.get_unchecked_mut(len)} += q as u8;
n -= d * q;

len += 1;

if n < 10 {
*unsafe {digits.get_unchecked_mut(len)} += n as u8;
break
}
}
unsafe {String::from_utf8_unchecked(digits[..len].into())}
}

#[inline(always)]
pub fn itoa_05(mut n: usize) -> String {
let mut buf = Vec::with_capacity(usize::ilog10(usize::MAX) as _);

{
if n >= 10_usize.pow(1) {
if n >= 10_usize.pow(2) {
if n >= 10_usize.pow(3) {
if n >= 10_usize.pow(4) {
if n >= 10_usize.pow(5) {
if n >= 10_usize.pow(6) {
if n >= 10_usize.pow(7) {
if n >= 10_usize.pow(8) {
if n >= 10_usize.pow(9) {
#[cfg(target_pointer_width="64")]
if n >= 10_usize.pow(10) {
if n >= 10_usize.pow(11) {
if n >= 10_usize.pow(12) {
if n >= 10_usize.pow(13) {
if n >= 10_usize.pow(14) {
if n >= 10_usize.pow(15) {
if n >= 10_usize.pow(16) {
if n >= 10_usize.pow(17) {
if n >= 10_usize.pow(18) {
if n >= 10_usize.pow(19) {
buf.push(b'0' + (n / 10_usize.pow(19)) as u8);
n %= 10_usize.pow(19)
}
buf.push(b'0' + (n / 10_usize.pow(18)) as u8);
n %= 10_usize.pow(18)
}
buf.push(b'0' + (n / 10_usize.pow(17)) as u8);
n %= 10_usize.pow(17)
}
buf.push(b'0' + (n / 10_usize.pow(16)) as u8);
n %= 10_usize.pow(16)
}
buf.push(b'0' + (n / 10_usize.pow(15)) as u8);
n %= 10_usize.pow(15)
}
buf.push(b'0' + (n / 10_usize.pow(14)) as u8);
n %= 10_usize.pow(14)
}
buf.push(b'0' + (n / 10_usize.pow(13)) as u8);
n %= 10_usize.pow(13)
}
buf.push(b'0' + (n / 10_usize.pow(12)) as u8);
n %= 10_usize.pow(12)
}
buf.push(b'0' + (n / 10_usize.pow(11)) as u8);
n %= 10_usize.pow(11)
}
buf.push(b'0' + (n / 10_usize.pow(10)) as u8);
n %= 10_usize.pow(10)
}
buf.push(b'0' + (n / 10_usize.pow(9)) as u8);
n %= 10_usize.pow(9)
}
buf.push(b'0' + (n / 10_usize.pow(8)) as u8);
n %= 10_usize.pow(8)
}
buf.push(b'0' + (n / 10_usize.pow(7)) as u8);
n %= 10_usize.pow(7)
}
buf.push(b'0' + (n / 10_usize.pow(6)) as u8);
n %= 10_usize.pow(6)
}
buf.push(b'0' + (n / 10_usize.pow(5)) as u8);
n %= 10_usize.pow(5)
}
buf.push(b'0' + (n / 10_usize.pow(4)) as u8);
n %= 10_usize.pow(4)
}
buf.push(b'0' + (n / 10_usize.pow(3)) as u8);
n %= 10_usize.pow(3)
}
buf.push(b'0' + (n / 10_usize.pow(2)) as u8);
n %= 10_usize.pow(2)
}
buf.push(b'0' + (n / 10_usize.pow(1)) as u8);
n %= 10_usize.pow(1)
}
buf.push(b'0' + n as u8)
}

unsafe {String::from_utf8_unchecked(buf)}
}

#[inline(always)]
pub fn itoa_06(mut n: usize) -> String {
let mut buf = Vec::<u8>::with_capacity(1 + usize::ilog10(usize::MAX) as usize);

{
macro_rules! push_unchecked {
($byte:expr) => {{
let len = buf.len();
std::ptr::write(buf.as_mut_ptr().add(len), $byte);
buf.set_len(len + 1);
}};
}

if n >= 10_usize.pow(1) {
if n >= 10_usize.pow(2) {
if n >= 10_usize.pow(3) {
if n >= 10_usize.pow(4) {
if n >= 10_usize.pow(5) {
if n >= 10_usize.pow(6) {
if n >= 10_usize.pow(7) {
if n >= 10_usize.pow(8) {
if n >= 10_usize.pow(9) {
#[cfg(target_pointer_width="64")]
if n >= 10_usize.pow(10) {
if n >= 10_usize.pow(11) {
if n >= 10_usize.pow(12) {
if n >= 10_usize.pow(13) {
if n >= 10_usize.pow(14) {
if n >= 10_usize.pow(15) {
if n >= 10_usize.pow(16) {
if n >= 10_usize.pow(17) {
if n >= 10_usize.pow(18) {
if n >= 10_usize.pow(19) {
let q = n / 10_usize.pow(19);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(19) * q
}
let q = n / 10_usize.pow(18);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(18) * q
}
let q = n / 10_usize.pow(17);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(17) * q
}
let q = n / 10_usize.pow(16);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(16) * q
}
let q = n / 10_usize.pow(15);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(15) * q
}
let q = n / 10_usize.pow(14);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(14) * q
}
let q = n / 10_usize.pow(13);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(13) * q
}
let q = n / 10_usize.pow(12);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(12) * q
}
let q = n / 10_usize.pow(11);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(11) * q
}
let q = n / 10_usize.pow(10);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(10) * q
}
let q = n / 10_usize.pow(9);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(9) * q
}
let q = n / 10_usize.pow(8);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(8) * q
}
let q = n / 10_usize.pow(7);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(7) * q
}
let q = n / 10_usize.pow(6);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(6) * q
}
let q = n / 10_usize.pow(5);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(5) * q
}
let q = n / 10_usize.pow(4);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(4) * q
}
let q = n / 10_usize.pow(3);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(3) * q
}
let q = n / 10_usize.pow(2);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(2) * q
}
let q = n / 10_usize.pow(1);
unsafe {push_unchecked!(b'0' + q as u8)}
n -= 10_usize.pow(1) * q
}
unsafe {push_unchecked!(b'0' + n as u8)}
}

unsafe {String::from_utf8_unchecked(buf)}
}
}

Expand All @@ -18,12 +348,17 @@ macro_rules! benchmark {
($( $target:ident )*) => {$(
#[bench]
fn $target(b: &mut test::Bencher) {
b.iter(|| for n in 0..42 {
b.iter(|| for n in 0..314 {
let _ = candiate::$target(test::black_box(n));
})
}
)*};
} benchmark! {
to_string
itoa
itoa_01
itoa_02
itoa_03
itoa_04
itoa_05
itoa_06
}

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