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Diffstat (limited to '')
-rw-r--r-- | vendor/ryu/src/d2s.rs | 300 |
1 files changed, 300 insertions, 0 deletions
diff --git a/vendor/ryu/src/d2s.rs b/vendor/ryu/src/d2s.rs new file mode 100644 index 000000000..392577a9a --- /dev/null +++ b/vendor/ryu/src/d2s.rs @@ -0,0 +1,300 @@ +// 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::*; +#[cfg(not(feature = "small"))] +pub use crate::d2s_full_table::*; +use crate::d2s_intrinsics::*; +#[cfg(feature = "small")] +pub use crate::d2s_small_table::*; +use core::mem::MaybeUninit; + +pub const DOUBLE_MANTISSA_BITS: u32 = 52; +pub const DOUBLE_EXPONENT_BITS: u32 = 11; +pub const DOUBLE_BIAS: i32 = 1023; +pub const DOUBLE_POW5_INV_BITCOUNT: i32 = 125; +pub const DOUBLE_POW5_BITCOUNT: i32 = 125; + +#[cfg_attr(feature = "no-panic", inline)] +pub fn decimal_length17(v: u64) -> u32 { + // This is slightly faster than a loop. + // The average output length is 16.38 digits, so we check high-to-low. + // Function precondition: v is not an 18, 19, or 20-digit number. + // (17 digits are sufficient for round-tripping.) + debug_assert!(v < 100000000000000000); + + if v >= 10000000000000000 { + 17 + } else if v >= 1000000000000000 { + 16 + } else if v >= 100000000000000 { + 15 + } else if v >= 10000000000000 { + 14 + } else if v >= 1000000000000 { + 13 + } else if v >= 100000000000 { + 12 + } else if v >= 10000000000 { + 11 + } else if v >= 1000000000 { + 10 + } else if v >= 100000000 { + 9 + } else if v >= 10000000 { + 8 + } else if v >= 1000000 { + 7 + } else if v >= 100000 { + 6 + } else if v >= 10000 { + 5 + } else if v >= 1000 { + 4 + } else if v >= 100 { + 3 + } else if v >= 10 { + 2 + } else { + 1 + } +} + +// A floating decimal representing m * 10^e. +pub struct FloatingDecimal64 { + pub mantissa: u64, + // Decimal exponent's range is -324 to 308 + // inclusive, and can fit in i16 if needed. + pub exponent: i32, +} + +#[cfg_attr(feature = "no-panic", inline)] +pub fn d2d(ieee_mantissa: u64, ieee_exponent: u32) -> FloatingDecimal64 { + let (e2, m2) = if ieee_exponent == 0 { + ( + // We subtract 2 so that the bounds computation has 2 additional bits. + 1 - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS as i32 - 2, + ieee_mantissa, + ) + } else { + ( + ieee_exponent as i32 - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS as i32 - 2, + (1u64 << DOUBLE_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; + // Implicit bool -> int conversion. True is 1, false is 0. + let mm_shift = (ieee_mantissa != 0 || ieee_exponent <= 1) as u32; + // We would compute mp and mm like this: + // uint64_t mp = 4 * m2 + 2; + // uint64_t mm = mv - 1 - mm_shift; + + // Step 3: Convert to a decimal power base using 128-bit arithmetic. + let mut vr: u64; + let mut vp: u64; + let mut vm: u64; + let mut vp_uninit: MaybeUninit<u64> = MaybeUninit::uninit(); + let mut vm_uninit: MaybeUninit<u64> = MaybeUninit::uninit(); + let e10: i32; + let mut vm_is_trailing_zeros = false; + let mut vr_is_trailing_zeros = false; + if e2 >= 0 { + // I tried special-casing q == 0, but there was no effect on performance. + // This expression is slightly faster than max(0, log10_pow2(e2) - 1). + let q = log10_pow2(e2) - (e2 > 3) as u32; + e10 = q as i32; + let k = DOUBLE_POW5_INV_BITCOUNT + pow5bits(q as i32) - 1; + let i = -e2 + q as i32 + k; + vr = unsafe { + mul_shift_all_64( + m2, + #[cfg(feature = "small")] + &compute_inv_pow5(q), + #[cfg(not(feature = "small"))] + { + debug_assert!(q < DOUBLE_POW5_INV_SPLIT.len() as u32); + DOUBLE_POW5_INV_SPLIT.get_unchecked(q as usize) + }, + i as u32, + vp_uninit.as_mut_ptr(), + vm_uninit.as_mut_ptr(), + mm_shift, + ) + }; + vp = unsafe { vp_uninit.assume_init() }; + vm = unsafe { vm_uninit.assume_init() }; + if q <= 21 { + // This should use q <= 22, but I think 21 is also safe. Smaller values + // may still be safe, but it's more difficult to reason about them. + // Only one of mp, mv, and mm can be a multiple of 5, if any. + let mv_mod5 = (mv as u32).wrapping_sub(5u32.wrapping_mul(div5(mv) as u32)); + if mv_mod5 == 0 { + vr_is_trailing_zeros = multiple_of_power_of_5(mv, q); + } else if accept_bounds { + // Same as min(e2 + (~mm & 1), pow5_factor(mm)) >= q + // <=> e2 + (~mm & 1) >= q && pow5_factor(mm) >= q + // <=> true && pow5_factor(mm) >= q, since e2 >= q. + vm_is_trailing_zeros = multiple_of_power_of_5(mv - 1 - mm_shift as u64, q); + } else { + // Same as min(e2 + 1, pow5_factor(mp)) >= q. + vp -= multiple_of_power_of_5(mv + 2, q) as u64; + } + } + } else { + // This expression is slightly faster than max(0, log10_pow5(-e2) - 1). + let q = log10_pow5(-e2) - (-e2 > 1) as u32; + e10 = q as i32 + e2; + let i = -e2 - q as i32; + let k = pow5bits(i) - DOUBLE_POW5_BITCOUNT; + let j = q as i32 - k; + vr = unsafe { + mul_shift_all_64( + m2, + #[cfg(feature = "small")] + &compute_pow5(i as u32), + #[cfg(not(feature = "small"))] + { + debug_assert!(i < DOUBLE_POW5_SPLIT.len() as i32); + DOUBLE_POW5_SPLIT.get_unchecked(i as usize) + }, + j as u32, + vp_uninit.as_mut_ptr(), + vm_uninit.as_mut_ptr(), + mm_shift, + ) + }; + vp = unsafe { vp_uninit.assume_init() }; + vm = unsafe { vm_uninit.assume_init() }; + 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 < 63 { + // TODO(ulfjack): Use a tighter bound here. + // We want to know if the full product has at least q trailing zeros. + // We need to compute min(p2(mv), p5(mv) - e2) >= q + // <=> p2(mv) >= q && p5(mv) - e2 >= q + // <=> p2(mv) >= q (because -e2 >= q) + vr_is_trailing_zeros = multiple_of_power_of_2(mv, q); + } + } + + // Step 4: Find the shortest decimal representation in the interval of valid representations. + let mut removed = 0i32; + let mut last_removed_digit = 0u8; + // On average, we remove ~2 digits. + let output = if vm_is_trailing_zeros || vr_is_trailing_zeros { + // General case, which happens rarely (~0.7%). + loop { + let vp_div10 = div10(vp); + let vm_div10 = div10(vm); + if vp_div10 <= vm_div10 { + break; + } + let vm_mod10 = (vm as u32).wrapping_sub(10u32.wrapping_mul(vm_div10 as u32)); + let vr_div10 = div10(vr); + let vr_mod10 = (vr as u32).wrapping_sub(10u32.wrapping_mul(vr_div10 as u32)); + vm_is_trailing_zeros &= vm_mod10 == 0; + vr_is_trailing_zeros &= last_removed_digit == 0; + last_removed_digit = vr_mod10 as u8; + vr = vr_div10; + vp = vp_div10; + vm = vm_div10; + removed += 1; + } + if vm_is_trailing_zeros { + loop { + let vm_div10 = div10(vm); + let vm_mod10 = (vm as u32).wrapping_sub(10u32.wrapping_mul(vm_div10 as u32)); + if vm_mod10 != 0 { + break; + } + let vp_div10 = div10(vp); + let vr_div10 = div10(vr); + let vr_mod10 = (vr as u32).wrapping_sub(10u32.wrapping_mul(vr_div10 as u32)); + vr_is_trailing_zeros &= last_removed_digit == 0; + last_removed_digit = vr_mod10 as u8; + vr = vr_div10; + vp = vp_div10; + vm = vm_div10; + 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 u64 + } else { + // Specialized for the common case (~99.3%). Percentages below are relative to this. + let mut round_up = false; + let vp_div100 = div100(vp); + let vm_div100 = div100(vm); + // Optimization: remove two digits at a time (~86.2%). + if vp_div100 > vm_div100 { + let vr_div100 = div100(vr); + let vr_mod100 = (vr as u32).wrapping_sub(100u32.wrapping_mul(vr_div100 as u32)); + round_up = vr_mod100 >= 50; + vr = vr_div100; + vp = vp_div100; + vm = vm_div100; + removed += 2; + } + // Loop iterations below (approximately), without optimization above: + // 0: 0.03%, 1: 13.8%, 2: 70.6%, 3: 14.0%, 4: 1.40%, 5: 0.14%, 6+: 0.02% + // Loop iterations below (approximately), with optimization above: + // 0: 70.6%, 1: 27.8%, 2: 1.40%, 3: 0.14%, 4+: 0.02% + loop { + let vp_div10 = div10(vp); + let vm_div10 = div10(vm); + if vp_div10 <= vm_div10 { + break; + } + let vr_div10 = div10(vr); + let vr_mod10 = (vr as u32).wrapping_sub(10u32.wrapping_mul(vr_div10 as u32)); + round_up = vr_mod10 >= 5; + vr = vr_div10; + vp = vp_div10; + vm = vm_div10; + removed += 1; + } + // We need to take vr + 1 if vr is outside bounds or we need to round up. + vr + (vr == vm || round_up) as u64 + }; + let exp = e10 + removed; + + FloatingDecimal64 { + exponent: exp, + mantissa: output, + } +} |