pxfm/
trunc.rs

1/*
2 * // Copyright (c) Radzivon Bartoshyk 6/2025. All rights reserved.
3 * //
4 * // Redistribution and use in source and binary forms, with or without modification,
5 * // are permitted provided that the following conditions are met:
6 * //
7 * // 1.  Redistributions of source code must retain the above copyright notice, this
8 * // list of conditions and the following disclaimer.
9 * //
10 * // 2.  Redistributions in binary form must reproduce the above copyright notice,
11 * // this list of conditions and the following disclaimer in the documentation
12 * // and/or other materials provided with the distribution.
13 * //
14 * // 3.  Neither the name of the copyright holder nor the names of its
15 * // contributors may be used to endorse or promote products derived from
16 * // this software without specific prior written permission.
17 * //
18 * // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
19 * // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
21 * // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
22 * // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
24 * // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
25 * // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
26 * // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
27 * // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 */
29use crate::bits::{get_exponent_f32, get_exponent_f64};
30
31#[inline]
32pub const fn truncf(x: f32) -> f32 {
33    // If x is infinity or NaN, return it.
34    // If it is zero also we should return it as is, but the logic
35    // later in this function takes care of it. But not doing a zero
36    // check, we improve the run time of non-zero values.
37    if x.is_infinite() || x.is_nan() {
38        return x;
39    }
40    const FRACTION_LENGTH: u32 = 23;
41    let exponent = get_exponent_f32(x);
42
43    // If the exponent is greater than the most negative mantissa
44    // exponent, then x is already an integer.
45    if exponent >= FRACTION_LENGTH as i32 {
46        return x;
47    }
48
49    // If the exponent is such that abs(x) is less than 1, then return 0.
50    if exponent <= -1 {
51        return if x.is_sign_negative() { -0.0 } else { 0.0 };
52    }
53    const FRACTION_MASK: u32 = (1 << FRACTION_LENGTH) - 1;
54    let trim_size = FRACTION_LENGTH as i32 - exponent;
55    let trunc_mantissa =
56        ((x.to_bits() & FRACTION_MASK) >> trim_size).wrapping_shl(trim_size as u32);
57
58    let prepared_bits = x.to_bits() & 0xFF800000;
59    f32::from_bits(prepared_bits | trunc_mantissa)
60}
61
62#[inline]
63pub const fn trunc(x: f64) -> f64 {
64    // If x is infinity or NaN, return it.
65    // If it is zero also we should return it as is, but the logic
66    // later in this function takes care of it. But not doing a zero
67    // check, we improve the run time of non-zero values.
68    if x.is_infinite() || x.is_nan() {
69        return x;
70    }
71    const FRACTION_LENGTH: u32 = 52;
72    let exponent = get_exponent_f64(x);
73
74    // If the exponent is greater than the most negative mantissa
75    // exponent, then x is already an integer.
76    if exponent >= FRACTION_LENGTH as i64 {
77        return x;
78    }
79
80    // If the exponent is such that abs(x) is less than 1, then return 0.
81    if exponent <= -1 {
82        return if x.is_sign_negative() { -0.0 } else { 0.0 };
83    }
84    const FRACTION_MASK: u64 = (1 << FRACTION_LENGTH) - 1;
85    let trim_size = FRACTION_LENGTH as i64 - exponent;
86    let trunc_mantissa =
87        ((x.to_bits() & FRACTION_MASK) >> trim_size).wrapping_shl(trim_size as u32);
88
89    let prepared_bits = x.to_bits() & 0xFFF0000000000000;
90    f64::from_bits(prepared_bits | trunc_mantissa)
91}
92
93#[cfg(test)]
94mod tests {
95    use super::*;
96
97    #[test]
98    fn test_truncf() {
99        assert_eq!(truncf(-1.0), -1.0);
100        assert_eq!(truncf(1.0), 1.0);
101        assert_eq!(truncf(1.234211), 1.0);
102        assert_eq!(truncf(-1.234211), -1.0);
103    }
104
105    #[test]
106    fn test_trunc() {
107        assert_eq!(trunc(-1.0), -1.0);
108        assert_eq!(trunc(1.0), 1.0);
109        assert_eq!(trunc(1.234211), 1.0);
110        assert_eq!(trunc(-1.234211), -1.0);
111    }
112}
pxfm/trunc.rs

pxfm/
trunc.rs
