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/* origin: FreeBSD /usr/src/lib/msun/src/e_sqrtf.c */
/*
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
*/
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
pub fn sqrtf(x: f32) -> f32 {
// On wasm32 we know that LLVM's intrinsic will compile to an optimized
// `f32.sqrt` native instruction, so we can leverage this for both code size
// and speed.
llvm_intrinsically_optimized! {
#[cfg(target_arch = "wasm32")] {
return if x < 0.0 {
::core::f32::NAN
} else {
unsafe { ::core::intrinsics::sqrtf32(x) }
}
}
}
#[cfg(target_feature = "sse")]
{
// Note: This path is unlikely since LLVM will usually have already
// optimized sqrt calls into hardware instructions if sse is available,
// but if someone does end up here they'll apprected the speed increase.
#[cfg(target_arch = "x86")]
use core::arch::x86::*;
#[cfg(target_arch = "x86_64")]
use core::arch::x86_64::*;
unsafe {
let m = _mm_set_ss(x);
let m_sqrt = _mm_sqrt_ss(m);
_mm_cvtss_f32(m_sqrt)
}
}
#[cfg(not(target_feature = "sse"))]
{
const TINY: f32 = 1.0e-30;
let mut z: f32;
let sign: i32 = 0x80000000u32 as i32;
let mut ix: i32;
let mut s: i32;
let mut q: i32;
let mut m: i32;
let mut t: i32;
let mut i: i32;
let mut r: u32;
ix = x.to_bits() as i32;
/* take care of Inf and NaN */
if (ix as u32 & 0x7f800000) == 0x7f800000 {
return x * x + x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf, sqrt(-inf)=sNaN */
}
/* take care of zero */
if ix <= 0 {
if (ix & !sign) == 0 {
return x; /* sqrt(+-0) = +-0 */
}
if ix < 0 {
return (x - x) / (x - x); /* sqrt(-ve) = sNaN */
}
}
/* normalize x */
m = ix >> 23;
if m == 0 {
/* subnormal x */
i = 0;
while ix & 0x00800000 == 0 {
ix <<= 1;
i = i + 1;
}
m -= i - 1;
}
m -= 127; /* unbias exponent */
ix = (ix & 0x007fffff) | 0x00800000;
if m & 1 == 1 {
/* odd m, double x to make it even */
ix += ix;
}
m >>= 1; /* m = [m/2] */
/* generate sqrt(x) bit by bit */
ix += ix;
q = 0;
s = 0;
r = 0x01000000; /* r = moving bit from right to left */
while r != 0 {
t = s + r as i32;
if t <= ix {
s = t + r as i32;
ix -= t;
q += r as i32;
}
ix += ix;
r >>= 1;
}
/* use floating add to find out rounding direction */
if ix != 0 {
z = 1.0 - TINY; /* raise inexact flag */
if z >= 1.0 {
z = 1.0 + TINY;
if z > 1.0 {
q += 2;
} else {
q += q & 1;
}
}
}
ix = (q >> 1) + 0x3f000000;
ix += m << 23;
f32::from_bits(ix as u32)
}
}
// PowerPC tests are failing on LLVM 13: https://github.com/rust-lang/rust/issues/88520
#[cfg(not(target_arch = "powerpc64"))]
#[cfg(test)]
mod tests {
use super::*;
use core::f32::*;
#[test]
fn sanity_check() {
assert_eq!(sqrtf(100.0), 10.0);
assert_eq!(sqrtf(4.0), 2.0);
}
/// The spec: https://en.cppreference.com/w/cpp/numeric/math/sqrt
#[test]
fn spec_tests() {
// Not Asserted: FE_INVALID exception is raised if argument is negative.
assert!(sqrtf(-1.0).is_nan());
assert!(sqrtf(NAN).is_nan());
for f in [0.0, -0.0, INFINITY].iter().copied() {
assert_eq!(sqrtf(f), f);
}
}
}
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