Use more efficient scheme for display u128/i128
Add zero padding Add benchmarks for fmt u128 This tests both when there is the max amount of work(all characters used) And least amount of work(1 character used)
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d62d3f7fa9
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3f1d2aadd1
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@ -108,3 +108,32 @@ fn write_str_macro_debug(bh: &mut Bencher) {
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}
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});
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}
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#[bench]
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fn write_u128_max(bh: &mut Bencher) {
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bh.iter(|| {
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std::hint::black_box(format!("{}", u128::MAX));
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});
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}
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#[bench]
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fn write_u128_min(bh: &mut Bencher) {
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bh.iter(|| {
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let s = format!("{}", 0u128);
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std::hint::black_box(s);
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});
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}
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#[bench]
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fn write_u64_max(bh: &mut Bencher) {
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bh.iter(|| {
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std::hint::black_box(format!("{}", u64::MAX));
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});
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}
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#[bench]
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fn write_u64_min(bh: &mut Bencher) {
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bh.iter(|| {
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std::hint::black_box(format!("{}", 0u64));
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});
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}
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@ -9,7 +9,7 @@ use crate::slice;
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use crate::str;
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#[doc(hidden)]
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trait Int:
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trait DisplayInt:
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PartialEq + PartialOrd + Div<Output = Self> + Rem<Output = Self> + Sub<Output = Self> + Copy
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{
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fn zero() -> Self;
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@ -21,8 +21,9 @@ trait Int:
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fn to_u128(&self) -> u128;
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}
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macro_rules! doit {
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($($t:ident)*) => ($(impl Int for $t {
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macro_rules! impl_int {
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($($t:ident)*) => (
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$(impl DisplayInt for $t {
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fn zero() -> Self { 0 }
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fn from_u8(u: u8) -> Self { u as Self }
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fn to_u8(&self) -> u8 { *self as u8 }
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@ -30,13 +31,29 @@ macro_rules! doit {
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fn to_u32(&self) -> u32 { *self as u32 }
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fn to_u64(&self) -> u64 { *self as u64 }
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fn to_u128(&self) -> u128 { *self as u128 }
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})*)
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})*
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)
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}
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doit! { i8 i16 i32 i64 i128 isize u8 u16 u32 u64 u128 usize }
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macro_rules! impl_uint {
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($($t:ident)*) => (
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$(impl DisplayInt for $t {
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fn zero() -> Self { 0 }
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fn from_u8(u: u8) -> Self { u as Self }
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fn to_u8(&self) -> u8 { *self as u8 }
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fn to_u16(&self) -> u16 { *self as u16 }
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fn to_u32(&self) -> u32 { *self as u32 }
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fn to_u64(&self) -> u64 { *self as u64 }
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fn to_u128(&self) -> u128 { *self as u128 }
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})*
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)
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}
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impl_int! { i8 i16 i32 i64 i128 isize }
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impl_uint! { u8 u16 u32 u64 u128 usize }
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/// A type that represents a specific radix
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#[doc(hidden)]
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trait GenericRadix {
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trait GenericRadix: Sized {
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/// The number of digits.
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const BASE: u8;
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@ -47,7 +64,7 @@ trait GenericRadix {
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fn digit(x: u8) -> u8;
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/// Format an integer using the radix using a formatter.
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fn fmt_int<T: Int>(&self, mut x: T, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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fn fmt_int<T: DisplayInt>(&self, mut x: T, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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// The radix can be as low as 2, so we need a buffer of at least 128
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// characters for a base 2 number.
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let zero = T::zero();
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@ -127,13 +144,11 @@ macro_rules! radix {
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radix! { Binary, 2, "0b", x @ 0 ..= 1 => b'0' + x }
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radix! { Octal, 8, "0o", x @ 0 ..= 7 => b'0' + x }
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radix! { LowerHex, 16, "0x", x @ 0 ..= 9 => b'0' + x,
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x @ 10 ..= 15 => b'a' + (x - 10) }
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radix! { UpperHex, 16, "0x", x @ 0 ..= 9 => b'0' + x,
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x @ 10 ..= 15 => b'A' + (x - 10) }
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radix! { LowerHex, 16, "0x", x @ 0 ..= 9 => b'0' + x, x @ 10 ..= 15 => b'a' + (x - 10) }
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radix! { UpperHex, 16, "0x", x @ 0 ..= 9 => b'0' + x, x @ 10 ..= 15 => b'A' + (x - 10) }
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macro_rules! int_base {
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($Trait:ident for $T:ident as $U:ident -> $Radix:ident) => {
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(fmt::$Trait:ident for $T:ident as $U:ident -> $Radix:ident) => {
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#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::$Trait for $T {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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@ -143,8 +158,27 @@ macro_rules! int_base {
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};
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}
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macro_rules! integer {
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($Int:ident, $Uint:ident) => {
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int_base! { fmt::Binary for $Int as $Uint -> Binary }
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int_base! { fmt::Octal for $Int as $Uint -> Octal }
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int_base! { fmt::LowerHex for $Int as $Uint -> LowerHex }
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int_base! { fmt::UpperHex for $Int as $Uint -> UpperHex }
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int_base! { fmt::Binary for $Uint as $Uint -> Binary }
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int_base! { fmt::Octal for $Uint as $Uint -> Octal }
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int_base! { fmt::LowerHex for $Uint as $Uint -> LowerHex }
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int_base! { fmt::UpperHex for $Uint as $Uint -> UpperHex }
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};
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}
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integer! { isize, usize }
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integer! { i8, u8 }
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integer! { i16, u16 }
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integer! { i32, u32 }
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integer! { i64, u64 }
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integer! { i128, u128 }
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macro_rules! debug {
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($T:ident) => {
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($($T:ident)*) => {$(
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#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::Debug for $T {
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#[inline]
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@ -158,31 +192,14 @@ macro_rules! debug {
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}
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}
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}
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};
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)*};
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}
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debug! {
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i8 i16 i32 i64 i128 isize
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u8 u16 u32 u64 u128 usize
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}
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macro_rules! integer {
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($Int:ident, $Uint:ident) => {
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int_base! { Binary for $Int as $Uint -> Binary }
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int_base! { Octal for $Int as $Uint -> Octal }
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int_base! { LowerHex for $Int as $Uint -> LowerHex }
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int_base! { UpperHex for $Int as $Uint -> UpperHex }
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debug! { $Int }
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int_base! { Binary for $Uint as $Uint -> Binary }
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int_base! { Octal for $Uint as $Uint -> Octal }
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int_base! { LowerHex for $Uint as $Uint -> LowerHex }
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int_base! { UpperHex for $Uint as $Uint -> UpperHex }
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debug! { $Uint }
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};
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}
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integer! { isize, usize }
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integer! { i8, u8 }
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integer! { i16, u16 }
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integer! { i32, u32 }
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integer! { i64, u64 }
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integer! { i128, u128 }
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// 2 digit decimal look up table
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static DEC_DIGITS_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\
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2021222324252627282930313233343536373839\
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4041424344454647484950515253545556575859\
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@ -256,8 +273,7 @@ macro_rules! impl_Display {
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f.pad_integral(is_nonnegative, "", buf_slice)
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}
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$(
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#[stable(feature = "rust1", since = "1.0.0")]
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$(#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::Display for $t {
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#[allow(unused_comparisons)]
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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@ -461,6 +477,185 @@ mod imp {
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impl_Exp!(i8, u8, i16, u16, i32, u32, isize, usize as u32 via to_u32 named exp_u32);
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impl_Exp!(i64, u64 as u64 via to_u64 named exp_u64);
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}
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impl_Display!(i128, u128 as u128 via to_u128 named fmt_u128);
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impl_Exp!(i128, u128 as u128 via to_u128 named exp_u128);
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/// Helper function for writing a u64 into `buf` going from last to first, with `curr`.
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fn parse_u64_into<const N: usize>(mut n: u64, buf: &mut [MaybeUninit<u8>; N], curr: &mut isize) {
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let buf_ptr = MaybeUninit::slice_as_mut_ptr(buf);
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let lut_ptr = DEC_DIGITS_LUT.as_ptr();
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assert!(*curr > 19);
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// SAFETY:
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// Writes at most 19 characters into the buffer. Guaranteed that any ptr into LUT is at most
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// 198, so will never OOB. There is a check above that there are at least 19 characters
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// remaining.
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unsafe {
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if n >= 1e16 as u64 {
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let to_parse = n % 1e16 as u64;
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n /= 1e16 as u64;
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// Some of these are nops but it looks more elegant this way.
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let d1 = ((to_parse / 1e14 as u64) % 100) << 1;
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let d2 = ((to_parse / 1e12 as u64) % 100) << 1;
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let d3 = ((to_parse / 1e10 as u64) % 100) << 1;
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let d4 = ((to_parse / 1e8 as u64) % 100) << 1;
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let d5 = ((to_parse / 1e6 as u64) % 100) << 1;
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let d6 = ((to_parse / 1e4 as u64) % 100) << 1;
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let d7 = ((to_parse / 1e2 as u64) % 100) << 1;
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let d8 = ((to_parse / 1e0 as u64) % 100) << 1;
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*curr -= 16;
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ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr + 0), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d2 as isize), buf_ptr.offset(*curr + 2), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d3 as isize), buf_ptr.offset(*curr + 4), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d4 as isize), buf_ptr.offset(*curr + 6), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d5 as isize), buf_ptr.offset(*curr + 8), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d6 as isize), buf_ptr.offset(*curr + 10), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d7 as isize), buf_ptr.offset(*curr + 12), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d8 as isize), buf_ptr.offset(*curr + 14), 2);
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}
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if n >= 1e8 as u64 {
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let to_parse = n % 1e8 as u64;
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n /= 1e8 as u64;
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// Some of these are nops but it looks more elegant this way.
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let d1 = ((to_parse / 1e6 as u64) % 100) << 1;
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let d2 = ((to_parse / 1e4 as u64) % 100) << 1;
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let d3 = ((to_parse / 1e2 as u64) % 100) << 1;
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let d4 = ((to_parse / 1e0 as u64) % 100) << 1;
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*curr -= 8;
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ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr + 0), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d2 as isize), buf_ptr.offset(*curr + 2), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d3 as isize), buf_ptr.offset(*curr + 4), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d4 as isize), buf_ptr.offset(*curr + 6), 2);
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}
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// `n` < 1e8 < (1 << 32)
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let mut n = n as u32;
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if n >= 1e4 as u32 {
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let to_parse = n % 1e4 as u32;
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n /= 1e4 as u32;
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let d1 = (to_parse / 100) << 1;
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let d2 = (to_parse % 100) << 1;
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*curr -= 4;
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ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr + 0), 2);
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ptr::copy_nonoverlapping(lut_ptr.offset(d2 as isize), buf_ptr.offset(*curr + 2), 2);
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}
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// `n` < 1e4 < (1 << 16)
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let mut n = n as u16;
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if n >= 100 {
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let d1 = (n % 100) << 1;
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n /= 100;
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*curr -= 2;
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ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr), 2);
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}
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// decode last 1 or 2 chars
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if n < 10 {
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*curr -= 1;
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*buf_ptr.offset(*curr) = (n as u8) + b'0';
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} else {
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let d1 = n << 1;
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*curr -= 2;
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ptr::copy_nonoverlapping(lut_ptr.offset(d1 as isize), buf_ptr.offset(*curr), 2);
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}
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::Display for u128 {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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fmt_u128(*self, true, f)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::Display for i128 {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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let is_nonnegative = *self >= 0;
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let n = if is_nonnegative {
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self.to_u128()
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} else {
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// convert the negative num to positive by summing 1 to it's 2 complement
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(!self.to_u128()).wrapping_add(1)
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};
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fmt_u128(n, is_nonnegative, f)
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}
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}
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/// Specialized optimization for u128. Instead of taking two items at a time, it splits
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/// into at most 2 u64s, and then chunks by 10e16, 10e8, 10e4, 10e2, and then 10e1.
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/// It also has to handle 1 last item, as 10^40 > 2^128 > 10^39, whereas
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/// 10^20 > 2^64 > 10^19.
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fn fmt_u128(n: u128, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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// 2^128 is about 3*10^38, so 39 gives an extra byte of space
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let mut buf = [MaybeUninit::<u8>::uninit(); 39];
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let mut curr = buf.len() as isize;
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let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
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let (n, rem) = udiv_1e19(n);
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parse_u64_into(rem, &mut buf, &mut curr);
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if n != 0 {
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// 0 pad up to point
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let target = (buf.len() - 19) as isize;
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// SAFETY: Guaranteed that we wrote at most 19 bytes, and there must be space
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// remaining since it has length 39
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unsafe {
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ptr::write_bytes(buf_ptr.offset(target), b'0', (curr - target) as usize);
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}
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curr = target;
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let (n, rem) = udiv_1e19(n);
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parse_u64_into(rem, &mut buf, &mut curr);
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// Should this following branch be annotated with unlikely?
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if n != 0 {
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let target = (buf.len() - 38) as isize;
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// SAFETY: At this point we wrote at most 38 bytes, pad up to that point,
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// There can only be at most 1 digit remaining.
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unsafe {
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ptr::write_bytes(buf_ptr.offset(target), b'0', (curr - target) as usize);
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curr = target - 1;
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*buf_ptr.offset(curr) = (n as u8) + b'0';
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}
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}
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}
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// SAFETY: `curr` > 0 (since we made `buf` large enough), and all the chars are valid
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// UTF-8 since `DEC_DIGITS_LUT` is
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let buf_slice = unsafe {
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str::from_utf8_unchecked(slice::from_raw_parts(
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buf_ptr.offset(curr),
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buf.len() - curr as usize,
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))
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};
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f.pad_integral(is_nonnegative, "", buf_slice)
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}
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/// Partition of `n` into n > 1e19 and rem <= 1e19
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fn udiv_1e19(n: u128) -> (u128, u64) {
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const DIV: u64 = 1e19 as u64;
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let high = (n >> 64) as u64;
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if high == 0 {
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let low = n as u64;
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return ((low / DIV) as u128, low % DIV);
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}
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let sr = 65 - high.leading_zeros();
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let mut q = n << (128 - sr);
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let mut r = n >> sr;
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let mut carry = 0;
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for _ in 0..sr {
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r = (r << 1) | (q >> 127);
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q = (q << 1) | carry as u128;
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let s = (DIV as u128).wrapping_sub(r).wrapping_sub(1) as i128 >> 127;
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carry = (s & 1) as u64;
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r -= (DIV as u128) & s as u128;
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}
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((q << 1) | carry as u128, r as u64)
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}
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