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Diffstat (limited to '')
-rw-r--r-- | vendor/ryu/src/f2s.rs | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/vendor/ryu/src/f2s.rs b/vendor/ryu/src/f2s.rs new file mode 100644 index 000000000..eeb457ac8 --- /dev/null +++ b/vendor/ryu/src/f2s.rs @@ -0,0 +1,176 @@ +// Translated from C to Rust. The original C code can be found at +// https://github.com/ulfjack/ryu and carries the following license: +// +// Copyright 2018 Ulf Adams +// +// The contents of this file may be used under the terms of the Apache License, +// Version 2.0. +// +// (See accompanying file LICENSE-Apache or copy at +// http://www.apache.org/licenses/LICENSE-2.0) +// +// Alternatively, the contents of this file may be used under the terms of +// the Boost Software License, Version 1.0. +// (See accompanying file LICENSE-Boost or copy at +// https://www.boost.org/LICENSE_1_0.txt) +// +// Unless required by applicable law or agreed to in writing, this software +// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. + +use crate::common::*; +use crate::f2s_intrinsics::*; + +pub const FLOAT_MANTISSA_BITS: u32 = 23; +pub const FLOAT_EXPONENT_BITS: u32 = 8; +const FLOAT_BIAS: i32 = 127; +pub use crate::f2s_intrinsics::{FLOAT_POW5_BITCOUNT, FLOAT_POW5_INV_BITCOUNT}; + +// A floating decimal representing m * 10^e. +pub struct FloatingDecimal32 { + pub mantissa: u32, + // Decimal exponent's range is -45 to 38 + // inclusive, and can fit in i16 if needed. + pub exponent: i32, +} + +#[cfg_attr(feature = "no-panic", inline)] +pub fn f2d(ieee_mantissa: u32, ieee_exponent: u32) -> FloatingDecimal32 { + let (e2, m2) = if ieee_exponent == 0 { + ( + // We subtract 2 so that the bounds computation has 2 additional bits. + 1 - FLOAT_BIAS - FLOAT_MANTISSA_BITS as i32 - 2, + ieee_mantissa, + ) + } else { + ( + ieee_exponent as i32 - FLOAT_BIAS - FLOAT_MANTISSA_BITS as i32 - 2, + (1u32 << FLOAT_MANTISSA_BITS) | ieee_mantissa, + ) + }; + let even = (m2 & 1) == 0; + let accept_bounds = even; + + // Step 2: Determine the interval of valid decimal representations. + let mv = 4 * m2; + let mp = 4 * m2 + 2; + // Implicit bool -> int conversion. True is 1, false is 0. + let mm_shift = (ieee_mantissa != 0 || ieee_exponent <= 1) as u32; + let mm = 4 * m2 - 1 - mm_shift; + + // Step 3: Convert to a decimal power base using 64-bit arithmetic. + let mut vr: u32; + let mut vp: u32; + let mut vm: u32; + let e10: i32; + let mut vm_is_trailing_zeros = false; + let mut vr_is_trailing_zeros = false; + let mut last_removed_digit = 0u8; + if e2 >= 0 { + let q = log10_pow2(e2); + e10 = q as i32; + let k = FLOAT_POW5_INV_BITCOUNT + pow5bits(q as i32) - 1; + let i = -e2 + q as i32 + k; + vr = mul_pow5_inv_div_pow2(mv, q, i); + vp = mul_pow5_inv_div_pow2(mp, q, i); + vm = mul_pow5_inv_div_pow2(mm, q, i); + if q != 0 && (vp - 1) / 10 <= vm / 10 { + // We need to know one removed digit even if we are not going to loop below. We could use + // q = X - 1 above, except that would require 33 bits for the result, and we've found that + // 32-bit arithmetic is faster even on 64-bit machines. + let l = FLOAT_POW5_INV_BITCOUNT + pow5bits(q as i32 - 1) - 1; + last_removed_digit = + (mul_pow5_inv_div_pow2(mv, q - 1, -e2 + q as i32 - 1 + l) % 10) as u8; + } + if q <= 9 { + // The largest power of 5 that fits in 24 bits is 5^10, but q <= 9 seems to be safe as well. + // Only one of mp, mv, and mm can be a multiple of 5, if any. + if mv % 5 == 0 { + vr_is_trailing_zeros = multiple_of_power_of_5_32(mv, q); + } else if accept_bounds { + vm_is_trailing_zeros = multiple_of_power_of_5_32(mm, q); + } else { + vp -= multiple_of_power_of_5_32(mp, q) as u32; + } + } + } else { + let q = log10_pow5(-e2); + e10 = q as i32 + e2; + let i = -e2 - q as i32; + let k = pow5bits(i) - FLOAT_POW5_BITCOUNT; + let mut j = q as i32 - k; + vr = mul_pow5_div_pow2(mv, i as u32, j); + vp = mul_pow5_div_pow2(mp, i as u32, j); + vm = mul_pow5_div_pow2(mm, i as u32, j); + if q != 0 && (vp - 1) / 10 <= vm / 10 { + j = q as i32 - 1 - (pow5bits(i + 1) - FLOAT_POW5_BITCOUNT); + last_removed_digit = (mul_pow5_div_pow2(mv, (i + 1) as u32, j) % 10) as u8; + } + if q <= 1 { + // {vr,vp,vm} is trailing zeros if {mv,mp,mm} has at least q trailing 0 bits. + // mv = 4 * m2, so it always has at least two trailing 0 bits. + vr_is_trailing_zeros = true; + if accept_bounds { + // mm = mv - 1 - mm_shift, so it has 1 trailing 0 bit iff mm_shift == 1. + vm_is_trailing_zeros = mm_shift == 1; + } else { + // mp = mv + 2, so it always has at least one trailing 0 bit. + vp -= 1; + } + } else if q < 31 { + // TODO(ulfjack): Use a tighter bound here. + vr_is_trailing_zeros = multiple_of_power_of_2_32(mv, q - 1); + } + } + + // Step 4: Find the shortest decimal representation in the interval of valid representations. + let mut removed = 0i32; + let output = if vm_is_trailing_zeros || vr_is_trailing_zeros { + // General case, which happens rarely (~4.0%). + while vp / 10 > vm / 10 { + vm_is_trailing_zeros &= vm - (vm / 10) * 10 == 0; + vr_is_trailing_zeros &= last_removed_digit == 0; + last_removed_digit = (vr % 10) as u8; + vr /= 10; + vp /= 10; + vm /= 10; + removed += 1; + } + if vm_is_trailing_zeros { + while vm % 10 == 0 { + vr_is_trailing_zeros &= last_removed_digit == 0; + last_removed_digit = (vr % 10) as u8; + vr /= 10; + vp /= 10; + vm /= 10; + removed += 1; + } + } + if vr_is_trailing_zeros && last_removed_digit == 5 && vr % 2 == 0 { + // Round even if the exact number is .....50..0. + last_removed_digit = 4; + } + // We need to take vr + 1 if vr is outside bounds or we need to round up. + vr + ((vr == vm && (!accept_bounds || !vm_is_trailing_zeros)) || last_removed_digit >= 5) + as u32 + } else { + // Specialized for the common case (~96.0%). Percentages below are relative to this. + // Loop iterations below (approximately): + // 0: 13.6%, 1: 70.7%, 2: 14.1%, 3: 1.39%, 4: 0.14%, 5+: 0.01% + while vp / 10 > vm / 10 { + last_removed_digit = (vr % 10) as u8; + vr /= 10; + vp /= 10; + vm /= 10; + removed += 1; + } + // We need to take vr + 1 if vr is outside bounds or we need to round up. + vr + (vr == vm || last_removed_digit >= 5) as u32 + }; + let exp = e10 + removed; + + FloatingDecimal32 { + exponent: exp, + mantissa: output, + } +} |