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implement LowerExp and UpperExp for integers #66721

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Feb 15, 2020
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implement LowerExp and UpperExp for integers #66721

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163 changes: 163 additions & 0 deletions src/libcore/fmt/num.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@

use crate::fmt;
use crate::mem::MaybeUninit;
use crate::num::flt2dec;
use crate::ops::{Div, Rem, Sub};
use crate::ptr;
use crate::slice;
Expand Down Expand Up @@ -256,6 +257,161 @@ macro_rules! impl_Display {
};
}

macro_rules! impl_Exp {
($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
fn $name(
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Before digging too deeply into the code itself can you offer any background on this implementation? Whether it's based on any common approaches used elsewhere?

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It is heavily based on impl_Display! from the same file. It also makes use of some stuff from float's implementation (for precision).

mut n: $u,
is_nonnegative: bool,
upper: bool,
f: &mut fmt::Formatter<'_>
) -> fmt::Result {
let (mut n, mut exponent, trailing_zeros, added_precision) = {
let mut exponent = 0;
// count and remove trailing decimal zeroes
while n % 10 == 0 && n >= 10 {
n /= 10;
exponent += 1;
}
let trailing_zeros = exponent;

let (added_precision, subtracted_precision) = match f.precision() {
Some(fmt_prec) => {
// number of decimal digits minus 1
let mut tmp = n;
let mut prec = 0;
while tmp >= 10 {
tmp /= 10;
prec += 1;
}
(fmt_prec.saturating_sub(prec), prec.saturating_sub(fmt_prec))
}
None => (0,0)
};
for _ in 1..subtracted_precision {
n/=10;
exponent += 1;
}
if subtracted_precision != 0 {
let rem = n % 10;
n /= 10;
exponent += 1;
// round up last digit
if rem >= 5 {
n += 1;
}
}
(n, exponent, trailing_zeros, added_precision)
};

// 39 digits (worst case u128) + . = 40
let mut buf = [MaybeUninit::<u8>::uninit(); 40];
let mut curr = buf.len() as isize; //index for buf
let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
let lut_ptr = DEC_DIGITS_LUT.as_ptr();

// decode 2 chars at a time
while n >= 100 {
let d1 = ((n % 100) as isize) << 1;
curr -= 2;
unsafe {
ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
}
n /= 100;
exponent += 2;
}
// n is <= 99, so at most 2 chars long
let mut n = n as isize; // possibly reduce 64bit math
// decode second-to-last character
if n >= 10 {
curr -= 1;
unsafe {
*buf_ptr.offset(curr) = (n as u8 % 10_u8) + b'0';
}
n /= 10;
exponent += 1;
}
// add decimal point iff >1 mantissa digit will be printed
if exponent != trailing_zeros || added_precision != 0 {
curr -= 1;
unsafe {
*buf_ptr.offset(curr) = b'.';
}
}

let buf_slice = unsafe {
// decode last character
curr -= 1;
*buf_ptr.offset(curr) = (n as u8) + b'0';

let len = buf.len() - curr as usize;
slice::from_raw_parts(buf_ptr.offset(curr), len)
};

// stores 'e' (or 'E') and the up to 2-digit exponent
let mut exp_buf = [MaybeUninit::<u8>::uninit(); 3];
let exp_ptr = MaybeUninit::first_ptr_mut(&mut exp_buf);
let exp_slice = unsafe {
*exp_ptr.offset(0) = if upper {b'E'} else {b'e'};
let len = if exponent < 10 {
*exp_ptr.offset(1) = (exponent as u8) + b'0';
2
} else {
let off = exponent << 1;
ptr::copy_nonoverlapping(lut_ptr.offset(off), exp_ptr.offset(1), 2);
3
};
slice::from_raw_parts(exp_ptr, len)
};

let parts = &[
flt2dec::Part::Copy(buf_slice),
flt2dec::Part::Zero(added_precision),
flt2dec::Part::Copy(exp_slice)
];
let sign = if !is_nonnegative {
&b"-"[..]
} else if f.sign_plus() {
&b"+"[..]
} else {
&b""[..]
};
let formatted = flt2dec::Formatted{sign, parts};
f.pad_formatted_parts(&formatted)
}

$(
#[stable(feature = "integer_exp_format", since = "1.42.0")]
impl fmt::LowerExp for $t {
#[allow(unused_comparisons)]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let is_nonnegative = *self >= 0;
let n = if is_nonnegative {
self.$conv_fn()
} else {
// convert the negative num to positive by summing 1 to it's 2 complement
(!self.$conv_fn()).wrapping_add(1)
};
$name(n, is_nonnegative, false, f)
}
})*
$(
#[stable(feature = "integer_exp_format", since = "1.42.0")]
impl fmt::UpperExp for $t {
#[allow(unused_comparisons)]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let is_nonnegative = *self >= 0;
let n = if is_nonnegative {
self.$conv_fn()
} else {
// convert the negative num to positive by summing 1 to it's 2 complement
(!self.$conv_fn()).wrapping_add(1)
};
$name(n, is_nonnegative, true, f)
}
})*
};
}

// 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"))]
Expand All @@ -265,13 +421,20 @@ mod imp {
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_Display!(i128, u128 as u128 via to_u128 named fmt_u128);
impl_Exp!(i128, u128 as u128 via to_u128 named exp_u128);
80 changes: 80 additions & 0 deletions src/libcore/tests/fmt/num.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,16 @@ fn test_format_int() {
assert_eq!(format!("{:o}", 1i16), "1");
assert_eq!(format!("{:o}", 1i32), "1");
assert_eq!(format!("{:o}", 1i64), "1");
assert_eq!(format!("{:e}", 1isize), "1e0");
assert_eq!(format!("{:e}", 1i8), "1e0");
assert_eq!(format!("{:e}", 1i16), "1e0");
assert_eq!(format!("{:e}", 1i32), "1e0");
assert_eq!(format!("{:e}", 1i64), "1e0");
assert_eq!(format!("{:E}", 1isize), "1E0");
assert_eq!(format!("{:E}", 1i8), "1E0");
assert_eq!(format!("{:E}", 1i16), "1E0");
assert_eq!(format!("{:E}", 1i32), "1E0");
assert_eq!(format!("{:E}", 1i64), "1E0");
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assert_eq!(format!("{}", 1usize), "1");
assert_eq!(format!("{}", 1u8), "1");
Expand Down Expand Up @@ -69,13 +79,79 @@ fn test_format_int() {
assert_eq!(format!("{:o}", 1u16), "1");
assert_eq!(format!("{:o}", 1u32), "1");
assert_eq!(format!("{:o}", 1u64), "1");
assert_eq!(format!("{:e}", 1u8), "1e0");
assert_eq!(format!("{:e}", 1u16), "1e0");
assert_eq!(format!("{:e}", 1u32), "1e0");
assert_eq!(format!("{:e}", 1u64), "1e0");
assert_eq!(format!("{:E}", 1u8), "1E0");
assert_eq!(format!("{:E}", 1u16), "1E0");
assert_eq!(format!("{:E}", 1u32), "1E0");
assert_eq!(format!("{:E}", 1u64), "1E0");

// Test a larger number
assert_eq!(format!("{:b}", 55), "110111");
assert_eq!(format!("{:o}", 55), "67");
assert_eq!(format!("{}", 55), "55");
assert_eq!(format!("{:x}", 55), "37");
assert_eq!(format!("{:X}", 55), "37");
assert_eq!(format!("{:e}", 55), "5.5e1");
assert_eq!(format!("{:E}", 55), "5.5E1");
assert_eq!(format!("{:e}", 10000000000u64), "1e10");
assert_eq!(format!("{:E}", 10000000000u64), "1E10");
assert_eq!(format!("{:e}", 10000000001u64), "1.0000000001e10");
assert_eq!(format!("{:E}", 10000000001u64), "1.0000000001E10");
}

#[test]
fn test_format_int_exp_limits() {
use core::{i128, i16, i32, i64, i8, u128, u16, u32, u64, u8};
assert_eq!(format!("{:e}", i8::MIN), "-1.28e2");
assert_eq!(format!("{:e}", i8::MAX), "1.27e2");
assert_eq!(format!("{:e}", i16::MIN), "-3.2768e4");
assert_eq!(format!("{:e}", i16::MAX), "3.2767e4");
assert_eq!(format!("{:e}", i32::MIN), "-2.147483648e9");
assert_eq!(format!("{:e}", i32::MAX), "2.147483647e9");
assert_eq!(format!("{:e}", i64::MIN), "-9.223372036854775808e18");
assert_eq!(format!("{:e}", i64::MAX), "9.223372036854775807e18");
assert_eq!(format!("{:e}", i128::MIN), "-1.70141183460469231731687303715884105728e38");
assert_eq!(format!("{:e}", i128::MAX), "1.70141183460469231731687303715884105727e38");

assert_eq!(format!("{:e}", u8::MAX), "2.55e2");
assert_eq!(format!("{:e}", u16::MAX), "6.5535e4");
assert_eq!(format!("{:e}", u32::MAX), "4.294967295e9");
assert_eq!(format!("{:e}", u64::MAX), "1.8446744073709551615e19");
assert_eq!(format!("{:e}", u128::MAX), "3.40282366920938463463374607431768211455e38");
}

#[test]
fn test_format_int_exp_precision() {
use core::{i128, i16, i32, i64, i8};

//test that float and integer match
let big_int: u32 = 314_159_265;
assert_eq!(format!("{:.1e}", big_int), format!("{:.1e}", f64::from(big_int)));

//test adding precision
assert_eq!(format!("{:.10e}", i8::MIN), "-1.2800000000e2");
assert_eq!(format!("{:.10e}", i16::MIN), "-3.2768000000e4");
assert_eq!(format!("{:.10e}", i32::MIN), "-2.1474836480e9");
assert_eq!(format!("{:.20e}", i64::MIN), "-9.22337203685477580800e18");
assert_eq!(format!("{:.40e}", i128::MIN), "-1.7014118346046923173168730371588410572800e38");

//test rounding
assert_eq!(format!("{:.1e}", i8::MIN), "-1.3e2");
assert_eq!(format!("{:.1e}", i16::MIN), "-3.3e4");
assert_eq!(format!("{:.1e}", i32::MIN), "-2.1e9");
assert_eq!(format!("{:.1e}", i64::MIN), "-9.2e18");
assert_eq!(format!("{:.1e}", i128::MIN), "-1.7e38");

//test huge precision
assert_eq!(format!("{:.1000e}", 1), format!("1.{}e0", "0".repeat(1000)));
//test zero precision
assert_eq!(format!("{:.0e}", 1), format!("1e0",));

//test padding with precision (and sign)
assert_eq!(format!("{:+10.3e}", 1), " +1.000e0");
}

#[test]
Expand All @@ -86,13 +162,17 @@ fn test_format_int_zero() {
assert_eq!(format!("{:o}", 0), "0");
assert_eq!(format!("{:x}", 0), "0");
assert_eq!(format!("{:X}", 0), "0");
assert_eq!(format!("{:e}", 0), "0e0");
assert_eq!(format!("{:E}", 0), "0E0");

assert_eq!(format!("{}", 0u32), "0");
assert_eq!(format!("{:?}", 0u32), "0");
assert_eq!(format!("{:b}", 0u32), "0");
assert_eq!(format!("{:o}", 0u32), "0");
assert_eq!(format!("{:x}", 0u32), "0");
assert_eq!(format!("{:X}", 0u32), "0");
assert_eq!(format!("{:e}", 0u32), "0e0");
assert_eq!(format!("{:E}", 0u32), "0E0");
}

#[test]
Expand Down