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/* SPDX-License-Identifier: MIT
* origin: musl src/math/trunc.c */
use crate::support::{Float, FpResult, Int, IntTy, MinInt, Status};
#[inline]
pub fn trunc<F: Float>(x: F) -> F {
trunc_status(x).val
}
#[inline]
pub fn trunc_status<F: Float>(x: F) -> FpResult<F> {
let mut xi: F::Int = x.to_bits();
let e: i32 = x.exp_unbiased();
// C1: The represented value has no fractional part, so no truncation is needed
if e >= F::SIG_BITS as i32 {
return FpResult::ok(x);
}
let mask = if e < 0 {
// C2: If the exponent is negative, the result will be zero so we mask out everything
// except the sign.
F::SIGN_MASK
} else {
// C3: Otherwise, we mask out the last `e` bits of the significand.
!(F::SIG_MASK >> e.unsigned())
};
// C4: If the to-be-masked-out portion is already zero, we have an exact result
if (xi & !mask) == IntTy::<F>::ZERO {
return FpResult::ok(x);
}
// C5: Otherwise the result is inexact and we will truncate. Raise `FE_INEXACT`, mask the
// result, and return.
let status = if xi & F::SIG_MASK == F::Int::ZERO {
Status::OK
} else {
Status::INEXACT
};
xi &= mask;
FpResult::new(F::from_bits(xi), status)
}
#[cfg(test)]
mod tests {
use super::*;
use crate::support::Hexf;
fn spec_test<F: Float>(cases: &[(F, F, Status)]) {
let roundtrip = [
F::ZERO,
F::ONE,
F::NEG_ONE,
F::NEG_ZERO,
F::INFINITY,
F::NEG_INFINITY,
];
for x in roundtrip {
let FpResult { val, status } = trunc_status(x);
assert_biteq!(val, x, "{}", Hexf(x));
assert_eq!(status, Status::OK, "{}", Hexf(x));
}
for &(x, res, res_stat) in cases {
let FpResult { val, status } = trunc_status(x);
assert_biteq!(val, res, "{}", Hexf(x));
assert_eq!(status, res_stat, "{}", Hexf(x));
}
}
/* Skipping f16 / f128 "sanity_check"s and spec cases due to rejected literal lexing at MSRV */
#[test]
#[cfg(f16_enabled)]
fn spec_tests_f16() {
let cases = [];
spec_test::<f16>(&cases);
}
#[test]
fn sanity_check_f32() {
assert_eq!(trunc(0.5f32), 0.0);
assert_eq!(trunc(1.1f32), 1.0);
assert_eq!(trunc(2.9f32), 2.0);
}
#[test]
fn spec_tests_f32() {
let cases = [
(0.1, 0.0, Status::INEXACT),
(-0.1, -0.0, Status::INEXACT),
(0.9, 0.0, Status::INEXACT),
(-0.9, -0.0, Status::INEXACT),
(1.1, 1.0, Status::INEXACT),
(-1.1, -1.0, Status::INEXACT),
(1.9, 1.0, Status::INEXACT),
(-1.9, -1.0, Status::INEXACT),
];
spec_test::<f32>(&cases);
assert_biteq!(trunc(1.1f32), 1.0);
assert_biteq!(trunc(1.1f64), 1.0);
// C1
assert_biteq!(trunc(hf32!("0x1p23")), hf32!("0x1p23"));
assert_biteq!(trunc(hf64!("0x1p52")), hf64!("0x1p52"));
assert_biteq!(trunc(hf32!("-0x1p23")), hf32!("-0x1p23"));
assert_biteq!(trunc(hf64!("-0x1p52")), hf64!("-0x1p52"));
// C2
assert_biteq!(trunc(hf32!("0x1p-1")), 0.0);
assert_biteq!(trunc(hf64!("0x1p-1")), 0.0);
assert_biteq!(trunc(hf32!("-0x1p-1")), -0.0);
assert_biteq!(trunc(hf64!("-0x1p-1")), -0.0);
}
#[test]
fn sanity_check_f64() {
assert_eq!(trunc(1.1f64), 1.0);
assert_eq!(trunc(2.9f64), 2.0);
}
#[test]
fn spec_tests_f64() {
let cases = [
(0.1, 0.0, Status::INEXACT),
(-0.1, -0.0, Status::INEXACT),
(0.9, 0.0, Status::INEXACT),
(-0.9, -0.0, Status::INEXACT),
(1.1, 1.0, Status::INEXACT),
(-1.1, -1.0, Status::INEXACT),
(1.9, 1.0, Status::INEXACT),
(-1.9, -1.0, Status::INEXACT),
];
spec_test::<f64>(&cases);
}
#[test]
#[cfg(f128_enabled)]
fn spec_tests_f128() {
let cases = [];
spec_test::<f128>(&cases);
}
}
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