| // 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::{log10_pow2, log10_pow5, pow5bits}; |
| #[cfg(not(feature = "small"))] |
| pub use crate::d2s_full_table::{DOUBLE_POW5_INV_SPLIT, DOUBLE_POW5_SPLIT}; |
| use crate::d2s_intrinsics::{ |
| div10, div100, div5, mul_shift_all_64, multiple_of_power_of_2, multiple_of_power_of_5, |
| }; |
| #[cfg(feature = "small")] |
| pub use crate::d2s_small_table::{compute_inv_pow5, compute_pow5}; |
| 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, |
| } |
| } |