vendor/ryu/src/f2s_intrinsics.rs

   1 // Translated from C to Rust. The original C code can be found at
   2 // https://github.com/ulfjack/ryu and carries the following license:
   3 //
   4 // Copyright 2018 Ulf Adams
   5 //
   6 // The contents of this file may be used under the terms of the Apache License,
   7 // Version 2.0.
   8 //
   9 //    (See accompanying file LICENSE-Apache or copy at
  10 //     http://www.apache.org/licenses/LICENSE-2.0)
  11 //
  12 // Alternatively, the contents of this file may be used under the terms of
  13 // the Boost Software License, Version 1.0.
  14 //    (See accompanying file LICENSE-Boost or copy at
  15 //     https://www.boost.org/LICENSE_1_0.txt)
  16 //
  17 // Unless required by applicable law or agreed to in writing, this software
  18 // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  19 // KIND, either express or implied.
  20
  21 use crate::d2s;
  22
  23 pub const FLOAT_POW5_INV_BITCOUNT: i32 = d2s::DOUBLE_POW5_INV_BITCOUNT - 64;
  24 pub const FLOAT_POW5_BITCOUNT: i32 = d2s::DOUBLE_POW5_BITCOUNT - 64;
  25
  26 #[cfg_attr(feature = "no-panic", inline)]
  27 fn pow5factor_32(mut value: u32) -> u32 {
  28     let mut count = 0u32;
  29     loop {
  30         debug_assert!(value != 0);
  31         let q = value / 5;
  32         let r = value % 5;
  33         if r != 0 {
  34             break;
  35         }
  36         value = q;
  37         count += 1;
  38     }
  39     count
  40 }
  41
  42 // Returns true if value is divisible by 5^p.
  43 #[cfg_attr(feature = "no-panic", inline)]
  44 pub fn multiple_of_power_of_5_32(value: u32, p: u32) -> bool {
  45     pow5factor_32(value) >= p
  46 }
  47
  48 // Returns true if value is divisible by 2^p.
  49 #[cfg_attr(feature = "no-panic", inline)]
  50 pub fn multiple_of_power_of_2_32(value: u32, p: u32) -> bool {
  51     // __builtin_ctz doesn't appear to be faster here.
  52     (value & ((1u32 << p) - 1)) == 0
  53 }
  54
  55 // It seems to be slightly faster to avoid uint128_t here, although the
  56 // generated code for uint128_t looks slightly nicer.
  57 #[cfg_attr(feature = "no-panic", inline)]
  58 fn mul_shift_32(m: u32, factor: u64, shift: i32) -> u32 {
  59     debug_assert!(shift > 32);
  60
  61     // The casts here help MSVC to avoid calls to the __allmul library
  62     // function.
  63     let factor_lo = factor as u32;
  64     let factor_hi = (factor >> 32) as u32;
  65     let bits0 = m as u64 * factor_lo as u64;
  66     let bits1 = m as u64 * factor_hi as u64;
  67
  68     let sum = (bits0 >> 32) + bits1;
  69     let shifted_sum = sum >> (shift - 32);
  70     debug_assert!(shifted_sum <= u32::max_value() as u64);
  71     shifted_sum as u32
  72 }
  73
  74 #[cfg_attr(feature = "no-panic", inline)]
  75 pub fn mul_pow5_inv_div_pow2(m: u32, q: u32, j: i32) -> u32 {
  76     #[cfg(feature = "small")]
  77     {
  78         // The inverse multipliers are defined as [2^x / 5^y] + 1; the upper 64
  79         // bits from the double lookup table are the correct bits for [2^x /
  80         // 5^y], so we have to add 1 here. Note that we rely on the fact that
  81         // the added 1 that's already stored in the table never overflows into
  82         // the upper 64 bits.
  83         let pow5 = unsafe { d2s::compute_inv_pow5(q) };
  84         mul_shift_32(m, pow5.1 + 1, j)
  85     }
  86
  87     #[cfg(not(feature = "small"))]
  88     {
  89         debug_assert!(q < d2s::DOUBLE_POW5_INV_SPLIT.len() as u32);
  90         unsafe {
  91             mul_shift_32(
  92                 m,
  93                 d2s::DOUBLE_POW5_INV_SPLIT.get_unchecked(q as usize).1 + 1,
  94                 j,
  95             )
  96         }
  97     }
  98 }
  99
 100 #[cfg_attr(feature = "no-panic", inline)]
 101 pub fn mul_pow5_div_pow2(m: u32, i: u32, j: i32) -> u32 {
 102     #[cfg(feature = "small")]
 103     {
 104         let pow5 = unsafe { d2s::compute_pow5(i) };
 105         mul_shift_32(m, pow5.1, j)
 106     }
 107
 108     #[cfg(not(feature = "small"))]
 109     {
 110         debug_assert!(i < d2s::DOUBLE_POW5_SPLIT.len() as u32);
 111         unsafe { mul_shift_32(m, d2s::DOUBLE_POW5_SPLIT.get_unchecked(i as usize).1, j) }
 112     }
 113 }