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Nov 25, 2024
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Reduce integer Display implementation size #133247

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d318878
Reduce integer `Display` implementation size
GuillaumeGomez Nov 20, 2024
0d4b52f
Improve code by using `unsigned_abs`
GuillaumeGomez Nov 20, 2024
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80 changes: 32 additions & 48 deletions library/core/src/fmt/num.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -199,32 +199,12 @@ static DEC_DIGITS_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\
8081828384858687888990919293949596979899";

macro_rules! impl_Display {
($($t:ident $(as $positive:ident)? named $name:ident,)* ; as $u:ident via $conv_fn:ident named $gen_name:ident) => {
($($signed:ident, $unsigned:ident,)* ; as $u:ident via $conv_fn:ident named $gen_name:ident) => {

$(
#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for $t {
impl fmt::Display for $unsigned {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// If it's a signed integer.
$(
let is_nonnegative = *self >= 0;

#[cfg(not(feature = "optimize_for_size"))]
{
if !is_nonnegative {
// convert the negative num to positive by summing 1 to its 2s complement
return (!self as $positive).wrapping_add(1)._fmt(false, f);
}
}
#[cfg(feature = "optimize_for_size")]
{
if !is_nonnegative {
// convert the negative num to positive by summing 1 to its 2s complement
return $gen_name((!self.$conv_fn()).wrapping_add(1), false, f);
}
}
)?
// If it's a positive integer.
#[cfg(not(feature = "optimize_for_size"))]
{
self._fmt(true, f)
Expand All @@ -236,10 +216,24 @@ macro_rules! impl_Display {
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl fmt::Display for $signed {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
#[cfg(not(feature = "optimize_for_size"))]
{
return self.unsigned_abs()._fmt(*self >= 0, f);
}
#[cfg(feature = "optimize_for_size")]
{
return $gen_name(self.unsigned_abs().$conv_fn(), *self >= 0, f);
}
}
}

#[cfg(not(feature = "optimize_for_size"))]
impl $t {
fn _fmt(mut self: $t, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
const SIZE: usize = $t::MAX.ilog(10) as usize + 1;
impl $unsigned {
fn _fmt(mut self, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
const SIZE: usize = $unsigned::MAX.ilog(10) as usize + 1;
let mut buf = [MaybeUninit::<u8>::uninit(); SIZE];
let mut curr = SIZE;
let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
Expand All @@ -258,7 +252,7 @@ macro_rules! impl_Display {
#[allow(unused_comparisons)]
// This block will be removed for smaller types at compile time and in the worst
// case, it will prevent to have the `10000` literal to overflow for `i8` and `u8`.
if core::mem::size_of::<$t>() >= 2 {
if core::mem::size_of::<$unsigned>() >= 2 {
// eagerly decode 4 characters at a time
while self >= 10000 {
let rem = (self % 10000) as usize;
Expand Down Expand Up @@ -312,8 +306,8 @@ macro_rules! impl_Display {

#[cfg(feature = "optimize_for_size")]
fn $gen_name(mut n: $u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// 2^128 is about 3*10^38, so 39 gives an extra byte of space
let mut buf = [MaybeUninit::<u8>::uninit(); 39];
const SIZE: usize = $u::MAX.ilog(10) as usize + 1;
let mut buf = [MaybeUninit::<u8>::uninit(); SIZE];
Comment on lines 307 to +310
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@workingjubilee workingjubilee Nov 22, 2024 •
edited
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? What is the effect of this change on binary size? Or is $u always the same?

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On smaller targets, the maximum size might be of u32 and not u64 so since we're there... But on the binary size, there should be no difference for this change.

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I see, hopefully so.

let mut curr = buf.len();
let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);

Expand Down Expand Up @@ -523,16 +517,11 @@ impl_Debug! {
mod imp {
use super::*;
impl_Display!(
i8 as u8 named fmt_i8,
u8 named fmt_u8,
i16 as u16 named fmt_i16,
u16 named fmt_u16,
i32 as u32 named fmt_i32,
u32 named fmt_u32,
i64 as u64 named fmt_i64,
u64 named fmt_u64,
isize as usize named fmt_isize,
usize named fmt_usize,
i8, u8,
i16, u16,
i32, u32,
i64, u64,
isize, usize,
; as u64 via to_u64 named fmt_u64
);
impl_Exp!(
Expand All @@ -545,18 +534,13 @@ mod imp {
mod imp {
use super::*;
impl_Display!(
i8 as u8 named fmt_i8,
u8 named fmt_u8,
i16 as u16 named fmt_i16,
u16 named fmt_u16,
i32 as u32 named fmt_i32,
u32 named fmt_u32,
isize as usize named fmt_isize,
usize named fmt_usize,
i8, u8,
i16, u16,
i32, u32,
isize, usize,
; as u32 via to_u32 named fmt_u32);
impl_Display!(
i64 as u64 named fmt_i64,
u64 named fmt_u64,
i64, u64,
; as u64 via to_u64 named fmt_u64);

impl_Exp!(i8, u8, i16, u16, i32, u32, isize, usize as u32 via to_u32 named exp_u32);
Expand Down
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