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-// 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,
- }
-}
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