ryu/
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
21use crate::d2s;
22
23pub const FLOAT_POW5_INV_BITCOUNT: i32 = d2s::DOUBLE_POW5_INV_BITCOUNT - 64;
24pub const FLOAT_POW5_BITCOUNT: i32 = d2s::DOUBLE_POW5_BITCOUNT - 64;
25
26#[cfg_attr(feature = "no-panic", inline)]
27fn 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)]
44pub 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)]
50pub 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)]
58fn 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)]
75pub 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)]
101pub 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}
ryu/f2s_intrinsics.rs

ryu/
f2s_intrinsics.rs
