mirror of https://github.com/rust-lang/rust
694 lines
26 KiB
Rust
694 lines
26 KiB
Rust
//! Integer and floating-point number formatting
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use crate::fmt;
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use crate::mem::MaybeUninit;
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use crate::num::fmt as numfmt;
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use crate::ops::{Div, Rem, Sub};
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use crate::ptr;
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use crate::slice;
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use crate::str;
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#[doc(hidden)]
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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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fn from_u8(u: u8) -> Self;
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fn to_u8(&self) -> u8;
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#[cfg(not(any(target_pointer_width = "64", target_arch = "wasm32")))]
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fn to_u32(&self) -> u32;
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fn to_u64(&self) -> u64;
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fn to_u128(&self) -> u128;
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}
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macro_rules! impl_int {
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($($t:ident)*) => (
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$(impl DisplayInt for $t {
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fn zero() -> Self { 0 }
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fn from_u8(u: u8) -> Self { u as Self }
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fn to_u8(&self) -> u8 { *self as u8 }
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#[cfg(not(any(target_pointer_width = "64", target_arch = "wasm32")))]
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fn to_u32(&self) -> u32 { *self as u32 }
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fn to_u64(&self) -> u64 { *self as u64 }
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fn to_u128(&self) -> u128 { *self as u128 }
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})*
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)
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}
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macro_rules! impl_uint {
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($($t:ident)*) => (
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$(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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#[cfg(not(any(target_pointer_width = "64", target_arch = "wasm32")))]
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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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///
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/// # Safety
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///
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/// `digit` must return an ASCII character.
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#[doc(hidden)]
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unsafe trait GenericRadix: Sized {
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/// The number of digits.
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const BASE: u8;
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/// A radix-specific prefix string.
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const PREFIX: &'static str;
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/// Converts an integer to corresponding radix digit.
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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: 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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let is_nonnegative = x >= zero;
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let mut buf = [MaybeUninit::<u8>::uninit(); 128];
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let mut curr = buf.len();
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let base = T::from_u8(Self::BASE);
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if is_nonnegative {
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// Accumulate each digit of the number from the least significant
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// to the most significant figure.
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for byte in buf.iter_mut().rev() {
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let n = x % base; // Get the current place value.
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x = x / base; // Deaccumulate the number.
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byte.write(Self::digit(n.to_u8())); // Store the digit in the buffer.
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curr -= 1;
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if x == zero {
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// No more digits left to accumulate.
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break;
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};
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}
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} else {
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// Do the same as above, but accounting for two's complement.
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for byte in buf.iter_mut().rev() {
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let n = zero - (x % base); // Get the current place value.
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x = x / base; // Deaccumulate the number.
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byte.write(Self::digit(n.to_u8())); // Store the digit in the buffer.
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curr -= 1;
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if x == zero {
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// No more digits left to accumulate.
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break;
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};
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}
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}
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let buf = &buf[curr..];
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// SAFETY: The only chars in `buf` are created by `Self::digit` which are assumed to be
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// valid UTF-8
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let buf = unsafe {
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str::from_utf8_unchecked(slice::from_raw_parts(
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MaybeUninit::slice_as_ptr(buf),
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buf.len(),
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))
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};
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f.pad_integral(is_nonnegative, Self::PREFIX, buf)
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}
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}
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/// A binary (base 2) radix
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#[derive(Clone, PartialEq)]
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struct Binary;
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/// An octal (base 8) radix
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#[derive(Clone, PartialEq)]
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struct Octal;
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/// A hexadecimal (base 16) radix, formatted with lower-case characters
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#[derive(Clone, PartialEq)]
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struct LowerHex;
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/// A hexadecimal (base 16) radix, formatted with upper-case characters
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#[derive(Clone, PartialEq)]
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struct UpperHex;
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macro_rules! radix {
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($T:ident, $base:expr, $prefix:expr, $($x:pat => $conv:expr),+) => {
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unsafe impl GenericRadix for $T {
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const BASE: u8 = $base;
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const PREFIX: &'static str = $prefix;
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fn digit(x: u8) -> u8 {
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match x {
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$($x => $conv,)+
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x => panic!("number not in the range 0..={}: {}", Self::BASE - 1, x),
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}
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}
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}
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}
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}
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radix! { Binary, 2, "0b", x @ 0 ..= 1 => b'0' + x }
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radix! { Octal, 8, "0o", x @ 0 ..= 7 => b'0' + x }
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radix! { LowerHex, 16, "0x", x @ 0 ..= 9 => b'0' + x, x @ 10 ..= 15 => b'a' + (x - 10) }
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radix! { UpperHex, 16, "0x", x @ 0 ..= 9 => b'0' + x, x @ 10 ..= 15 => b'A' + (x - 10) }
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macro_rules! int_base {
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(fmt::$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 $T {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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$Radix.fmt_int(*self as $U, f)
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}
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}
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};
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}
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macro_rules! integer {
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($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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#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::Debug for $T {
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#[inline]
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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if f.debug_lower_hex() {
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fmt::LowerHex::fmt(self, f)
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} else if f.debug_upper_hex() {
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fmt::UpperHex::fmt(self, f)
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} else {
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fmt::Display::fmt(self, f)
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}
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}
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}
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)*};
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}
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debug! {
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i8 i16 i32 i64 i128 isize
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u8 u16 u32 u64 u128 usize
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}
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// 2 digit decimal look up table
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static DEC_DIGITS_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\
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2021222324252627282930313233343536373839\
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4041424344454647484950515253545556575859\
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6061626364656667686970717273747576777879\
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8081828384858687888990919293949596979899";
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macro_rules! impl_Display {
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($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
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fn $name(mut n: $u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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// 2^128 is about 3*10^38, so 39 gives an extra byte of space
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let mut buf = [MaybeUninit::<u8>::uninit(); 39];
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let mut curr = buf.len();
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let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
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let lut_ptr = DEC_DIGITS_LUT.as_ptr();
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// SAFETY: Since `d1` and `d2` are always less than or equal to `198`, we
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// can copy from `lut_ptr[d1..d1 + 1]` and `lut_ptr[d2..d2 + 1]`. To show
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// that it's OK to copy into `buf_ptr`, notice that at the beginning
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// `curr == buf.len() == 39 > log(n)` since `n < 2^128 < 10^39`, and at
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// each step this is kept the same as `n` is divided. Since `n` is always
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// non-negative, this means that `curr > 0` so `buf_ptr[curr..curr + 1]`
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// is safe to access.
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unsafe {
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// need at least 16 bits for the 4-characters-at-a-time to work.
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assert!(crate::mem::size_of::<$u>() >= 2);
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// eagerly decode 4 characters at a time
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while n >= 10000 {
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let rem = (n % 10000) as usize;
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n /= 10000;
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let d1 = (rem / 100) << 1;
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let d2 = (rem % 100) << 1;
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curr -= 4;
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// We are allowed to copy to `buf_ptr[curr..curr + 3]` here since
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// otherwise `curr < 0`. But then `n` was originally at least `10000^10`
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// which is `10^40 > 2^128 > n`.
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ptr::copy_nonoverlapping(lut_ptr.add(d1), buf_ptr.add(curr), 2);
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ptr::copy_nonoverlapping(lut_ptr.add(d2), buf_ptr.add(curr + 2), 2);
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}
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// if we reach here numbers are <= 9999, so at most 4 chars long
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let mut n = n as usize; // possibly reduce 64bit math
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// decode 2 more chars, if > 2 chars
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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.add(d1), buf_ptr.add(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.add(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.add(d1), buf_ptr.add(curr), 2);
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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(
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slice::from_raw_parts(buf_ptr.add(curr), buf.len() - curr))
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};
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f.pad_integral(is_nonnegative, "", buf_slice)
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}
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$(#[stable(feature = "rust1", since = "1.0.0")]
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impl fmt::Display for $t {
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#[allow(unused_comparisons)]
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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let is_nonnegative = *self >= 0;
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let n = if is_nonnegative {
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self.$conv_fn()
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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.$conv_fn()).wrapping_add(1)
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};
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$name(n, is_nonnegative, f)
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}
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})*
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};
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}
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macro_rules! impl_Exp {
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($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
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fn $name(
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mut n: $u,
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is_nonnegative: bool,
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upper: bool,
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f: &mut fmt::Formatter<'_>
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) -> fmt::Result {
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let (mut n, mut exponent, trailing_zeros, added_precision) = {
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let mut exponent = 0;
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// count and remove trailing decimal zeroes
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while n % 10 == 0 && n >= 10 {
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n /= 10;
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exponent += 1;
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}
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let (added_precision, subtracted_precision) = match f.precision() {
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Some(fmt_prec) => {
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// number of decimal digits minus 1
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let mut tmp = n;
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let mut prec = 0;
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while tmp >= 10 {
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tmp /= 10;
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prec += 1;
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}
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(fmt_prec.saturating_sub(prec), prec.saturating_sub(fmt_prec))
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}
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None => (0, 0)
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};
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for _ in 1..subtracted_precision {
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n /= 10;
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exponent += 1;
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}
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if subtracted_precision != 0 {
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let rem = n % 10;
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n /= 10;
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exponent += 1;
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// round up last digit, round to even on a tie
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if rem > 5 || (rem == 5 && (n % 2 != 0 || subtracted_precision > 1 )) {
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n += 1;
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// if the digit is rounded to the next power
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// instead adjust the exponent
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if n.ilog10() > (n - 1).ilog10() {
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n /= 10;
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exponent += 1;
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}
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}
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}
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(n, exponent, exponent, added_precision)
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};
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// 39 digits (worst case u128) + . = 40
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// Since `curr` always decreases by the number of digits copied, this means
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// that `curr >= 0`.
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let mut buf = [MaybeUninit::<u8>::uninit(); 40];
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let mut curr = buf.len(); //index for buf
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let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
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let lut_ptr = DEC_DIGITS_LUT.as_ptr();
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// decode 2 chars at a time
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while n >= 100 {
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let d1 = ((n % 100) as usize) << 1;
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curr -= 2;
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// SAFETY: `d1 <= 198`, so we can copy from `lut_ptr[d1..d1 + 2]` since
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// `DEC_DIGITS_LUT` has a length of 200.
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unsafe {
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ptr::copy_nonoverlapping(lut_ptr.add(d1), buf_ptr.add(curr), 2);
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}
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n /= 100;
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exponent += 2;
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}
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// n is <= 99, so at most 2 chars long
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let mut n = n as isize; // possibly reduce 64bit math
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// decode second-to-last character
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if n >= 10 {
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curr -= 1;
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// SAFETY: Safe since `40 > curr >= 0` (see comment)
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unsafe {
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*buf_ptr.add(curr) = (n as u8 % 10_u8) + b'0';
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}
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n /= 10;
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exponent += 1;
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}
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// add decimal point iff >1 mantissa digit will be printed
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if exponent != trailing_zeros || added_precision != 0 {
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curr -= 1;
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// SAFETY: Safe since `40 > curr >= 0`
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unsafe {
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*buf_ptr.add(curr) = b'.';
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}
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}
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// SAFETY: Safe since `40 > curr >= 0`
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let buf_slice = unsafe {
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// decode last character
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curr -= 1;
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*buf_ptr.add(curr) = (n as u8) + b'0';
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let len = buf.len() - curr as usize;
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slice::from_raw_parts(buf_ptr.add(curr), len)
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};
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// stores 'e' (or 'E') and the up to 2-digit exponent
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let mut exp_buf = [MaybeUninit::<u8>::uninit(); 3];
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let exp_ptr = MaybeUninit::slice_as_mut_ptr(&mut exp_buf);
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// SAFETY: In either case, `exp_buf` is written within bounds and `exp_ptr[..len]`
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// is contained within `exp_buf` since `len <= 3`.
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let exp_slice = unsafe {
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*exp_ptr.add(0) = if upper { b'E' } else { b'e' };
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let len = if exponent < 10 {
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*exp_ptr.add(1) = (exponent as u8) + b'0';
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2
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} else {
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let off = exponent << 1;
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ptr::copy_nonoverlapping(lut_ptr.add(off), exp_ptr.add(1), 2);
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3
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};
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slice::from_raw_parts(exp_ptr, len)
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};
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let parts = &[
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numfmt::Part::Copy(buf_slice),
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numfmt::Part::Zero(added_precision),
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numfmt::Part::Copy(exp_slice),
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];
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let sign = if !is_nonnegative {
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"-"
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} else if f.sign_plus() {
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"+"
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} else {
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""
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};
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let formatted = numfmt::Formatted { sign, parts };
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// SAFETY: `buf_slice` and `exp_slice` contain only ASCII characters.
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unsafe { f.pad_formatted_parts(&formatted) }
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}
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$(
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#[stable(feature = "integer_exp_format", since = "1.42.0")]
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impl fmt::LowerExp for $t {
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#[allow(unused_comparisons)]
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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let is_nonnegative = *self >= 0;
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let n = if is_nonnegative {
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self.$conv_fn()
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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.$conv_fn()).wrapping_add(1)
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};
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$name(n, is_nonnegative, false, f)
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}
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})*
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$(
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#[stable(feature = "integer_exp_format", since = "1.42.0")]
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impl fmt::UpperExp for $t {
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#[allow(unused_comparisons)]
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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let is_nonnegative = *self >= 0;
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let n = if is_nonnegative {
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self.$conv_fn()
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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.$conv_fn()).wrapping_add(1)
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};
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$name(n, is_nonnegative, true, f)
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}
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})*
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};
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}
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// Include wasm32 in here since it doesn't reflect the native pointer size, and
|
||
// often cares strongly about getting a smaller code size.
|
||
#[cfg(any(target_pointer_width = "64", target_arch = "wasm32"))]
|
||
mod imp {
|
||
use super::*;
|
||
impl_Display!(
|
||
i8, u8, i16, u16, i32, u32, i64, u64, usize, isize
|
||
as u64 via to_u64 named fmt_u64
|
||
);
|
||
impl_Exp!(
|
||
i8, u8, i16, u16, i32, u32, i64, u64, usize, isize
|
||
as u64 via to_u64 named exp_u64
|
||
);
|
||
}
|
||
|
||
#[cfg(not(any(target_pointer_width = "64", target_arch = "wasm32")))]
|
||
mod imp {
|
||
use super::*;
|
||
impl_Display!(i8, u8, i16, u16, i32, u32, isize, usize as u32 via to_u32 named fmt_u32);
|
||
impl_Display!(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);
|
||
impl_Exp!(i64, u64 as u64 via to_u64 named exp_u64);
|
||
}
|
||
impl_Exp!(i128, u128 as u128 via to_u128 named exp_u128);
|
||
|
||
/// Helper function for writing a u64 into `buf` going from last to first, with `curr`.
|
||
fn parse_u64_into<const N: usize>(mut n: u64, buf: &mut [MaybeUninit<u8>; N], curr: &mut usize) {
|
||
let buf_ptr = MaybeUninit::slice_as_mut_ptr(buf);
|
||
let lut_ptr = DEC_DIGITS_LUT.as_ptr();
|
||
assert!(*curr > 19);
|
||
|
||
// SAFETY:
|
||
// Writes at most 19 characters into the buffer. Guaranteed that any ptr into LUT is at most
|
||
// 198, so will never OOB. There is a check above that there are at least 19 characters
|
||
// remaining.
|
||
unsafe {
|
||
if n >= 1e16 as u64 {
|
||
let to_parse = n % 1e16 as u64;
|
||
n /= 1e16 as u64;
|
||
|
||
// Some of these are nops but it looks more elegant this way.
|
||
let d1 = ((to_parse / 1e14 as u64) % 100) << 1;
|
||
let d2 = ((to_parse / 1e12 as u64) % 100) << 1;
|
||
let d3 = ((to_parse / 1e10 as u64) % 100) << 1;
|
||
let d4 = ((to_parse / 1e8 as u64) % 100) << 1;
|
||
let d5 = ((to_parse / 1e6 as u64) % 100) << 1;
|
||
let d6 = ((to_parse / 1e4 as u64) % 100) << 1;
|
||
let d7 = ((to_parse / 1e2 as u64) % 100) << 1;
|
||
let d8 = ((to_parse / 1e0 as u64) % 100) << 1;
|
||
|
||
*curr -= 16;
|
||
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr + 0), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d2 as usize), buf_ptr.add(*curr + 2), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d3 as usize), buf_ptr.add(*curr + 4), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d4 as usize), buf_ptr.add(*curr + 6), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d5 as usize), buf_ptr.add(*curr + 8), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d6 as usize), buf_ptr.add(*curr + 10), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d7 as usize), buf_ptr.add(*curr + 12), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d8 as usize), buf_ptr.add(*curr + 14), 2);
|
||
}
|
||
if n >= 1e8 as u64 {
|
||
let to_parse = n % 1e8 as u64;
|
||
n /= 1e8 as u64;
|
||
|
||
// Some of these are nops but it looks more elegant this way.
|
||
let d1 = ((to_parse / 1e6 as u64) % 100) << 1;
|
||
let d2 = ((to_parse / 1e4 as u64) % 100) << 1;
|
||
let d3 = ((to_parse / 1e2 as u64) % 100) << 1;
|
||
let d4 = ((to_parse / 1e0 as u64) % 100) << 1;
|
||
*curr -= 8;
|
||
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr + 0), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d2 as usize), buf_ptr.add(*curr + 2), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d3 as usize), buf_ptr.add(*curr + 4), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d4 as usize), buf_ptr.add(*curr + 6), 2);
|
||
}
|
||
// `n` < 1e8 < (1 << 32)
|
||
let mut n = n as u32;
|
||
if n >= 1e4 as u32 {
|
||
let to_parse = n % 1e4 as u32;
|
||
n /= 1e4 as u32;
|
||
|
||
let d1 = (to_parse / 100) << 1;
|
||
let d2 = (to_parse % 100) << 1;
|
||
*curr -= 4;
|
||
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr + 0), 2);
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d2 as usize), buf_ptr.add(*curr + 2), 2);
|
||
}
|
||
|
||
// `n` < 1e4 < (1 << 16)
|
||
let mut n = n as u16;
|
||
if n >= 100 {
|
||
let d1 = (n % 100) << 1;
|
||
n /= 100;
|
||
*curr -= 2;
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr), 2);
|
||
}
|
||
|
||
// decode last 1 or 2 chars
|
||
if n < 10 {
|
||
*curr -= 1;
|
||
*buf_ptr.add(*curr) = (n as u8) + b'0';
|
||
} else {
|
||
let d1 = n << 1;
|
||
*curr -= 2;
|
||
ptr::copy_nonoverlapping(lut_ptr.add(d1 as usize), buf_ptr.add(*curr), 2);
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl fmt::Display for u128 {
|
||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||
fmt_u128(*self, true, f)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl fmt::Display for i128 {
|
||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||
let is_nonnegative = *self >= 0;
|
||
let n = if is_nonnegative {
|
||
self.to_u128()
|
||
} else {
|
||
// convert the negative num to positive by summing 1 to it's 2 complement
|
||
(!self.to_u128()).wrapping_add(1)
|
||
};
|
||
fmt_u128(n, is_nonnegative, f)
|
||
}
|
||
}
|
||
|
||
/// Specialized optimization for u128. Instead of taking two items at a time, it splits
|
||
/// into at most 2 u64s, and then chunks by 10e16, 10e8, 10e4, 10e2, and then 10e1.
|
||
/// It also has to handle 1 last item, as 10^40 > 2^128 > 10^39, whereas
|
||
/// 10^20 > 2^64 > 10^19.
|
||
fn fmt_u128(n: u128, 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];
|
||
let mut curr = buf.len();
|
||
|
||
let (n, rem) = udiv_1e19(n);
|
||
parse_u64_into(rem, &mut buf, &mut curr);
|
||
|
||
if n != 0 {
|
||
// 0 pad up to point
|
||
let target = buf.len() - 19;
|
||
// SAFETY: Guaranteed that we wrote at most 19 bytes, and there must be space
|
||
// remaining since it has length 39
|
||
unsafe {
|
||
ptr::write_bytes(
|
||
MaybeUninit::slice_as_mut_ptr(&mut buf).add(target),
|
||
b'0',
|
||
curr - target,
|
||
);
|
||
}
|
||
curr = target;
|
||
|
||
let (n, rem) = udiv_1e19(n);
|
||
parse_u64_into(rem, &mut buf, &mut curr);
|
||
// Should this following branch be annotated with unlikely?
|
||
if n != 0 {
|
||
let target = buf.len() - 38;
|
||
// The raw `buf_ptr` pointer is only valid until `buf` is used the next time,
|
||
// buf `buf` is not used in this scope so we are good.
|
||
let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
|
||
// SAFETY: At this point we wrote at most 38 bytes, pad up to that point,
|
||
// There can only be at most 1 digit remaining.
|
||
unsafe {
|
||
ptr::write_bytes(buf_ptr.add(target), b'0', curr - target);
|
||
curr = target - 1;
|
||
*buf_ptr.add(curr) = (n as u8) + b'0';
|
||
}
|
||
}
|
||
}
|
||
|
||
// SAFETY: `curr` > 0 (since we made `buf` large enough), and all the chars are valid
|
||
// UTF-8 since `DEC_DIGITS_LUT` is
|
||
let buf_slice = unsafe {
|
||
str::from_utf8_unchecked(slice::from_raw_parts(
|
||
MaybeUninit::slice_as_mut_ptr(&mut buf).add(curr),
|
||
buf.len() - curr,
|
||
))
|
||
};
|
||
f.pad_integral(is_nonnegative, "", buf_slice)
|
||
}
|
||
|
||
/// Partition of `n` into n > 1e19 and rem <= 1e19
|
||
///
|
||
/// Integer division algorithm is based on the following paper:
|
||
///
|
||
/// T. Granlund and P. Montgomery, “Division by Invariant Integers Using Multiplication”
|
||
/// in Proc. of the SIGPLAN94 Conference on Programming Language Design and
|
||
/// Implementation, 1994, pp. 61–72
|
||
///
|
||
fn udiv_1e19(n: u128) -> (u128, u64) {
|
||
const DIV: u64 = 1e19 as u64;
|
||
const FACTOR: u128 = 156927543384667019095894735580191660403;
|
||
|
||
let quot = if n < 1 << 83 {
|
||
((n >> 19) as u64 / (DIV >> 19)) as u128
|
||
} else {
|
||
u128_mulhi(n, FACTOR) >> 62
|
||
};
|
||
|
||
let rem = (n - quot * DIV as u128) as u64;
|
||
(quot, rem)
|
||
}
|
||
|
||
/// Multiply unsigned 128 bit integers, return upper 128 bits of the result
|
||
#[inline]
|
||
fn u128_mulhi(x: u128, y: u128) -> u128 {
|
||
let x_lo = x as u64;
|
||
let x_hi = (x >> 64) as u64;
|
||
let y_lo = y as u64;
|
||
let y_hi = (y >> 64) as u64;
|
||
|
||
// handle possibility of overflow
|
||
let carry = (x_lo as u128 * y_lo as u128) >> 64;
|
||
let m = x_lo as u128 * y_hi as u128 + carry;
|
||
let high1 = m >> 64;
|
||
|
||
let m_lo = m as u64;
|
||
let high2 = (x_hi as u128 * y_lo as u128 + m_lo as u128) >> 64;
|
||
|
||
x_hi as u128 * y_hi as u128 + high1 + high2
|
||
}
|