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Diffstat (limited to '')
| -rw-r--r-- | vendor/compiler_builtins/libm/src/math/sqrt.rs | 264 |
1 files changed, 264 insertions, 0 deletions
diff --git a/vendor/compiler_builtins/libm/src/math/sqrt.rs b/vendor/compiler_builtins/libm/src/math/sqrt.rs new file mode 100644 index 000000000..f06b209a4 --- /dev/null +++ b/vendor/compiler_builtins/libm/src/math/sqrt.rs @@ -0,0 +1,264 @@ +/* origin: FreeBSD /usr/src/lib/msun/src/e_sqrt.c */ +/* + * ==================================================== + * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. + * + * Developed at SunSoft, a Sun Microsystems, Inc. business. + * Permission to use, copy, modify, and distribute this + * software is freely granted, provided that this notice + * is preserved. + * ==================================================== + */ +/* sqrt(x) + * Return correctly rounded sqrt. + * ------------------------------------------ + * | Use the hardware sqrt if you have one | + * ------------------------------------------ + * Method: + * Bit by bit method using integer arithmetic. (Slow, but portable) + * 1. Normalization + * Scale x to y in [1,4) with even powers of 2: + * find an integer k such that 1 <= (y=x*2^(2k)) < 4, then + * sqrt(x) = 2^k * sqrt(y) + * 2. Bit by bit computation + * Let q = sqrt(y) truncated to i bit after binary point (q = 1), + * i 0 + * i+1 2 + * s = 2*q , and y = 2 * ( y - q ). (1) + * i i i i + * + * To compute q from q , one checks whether + * i+1 i + * + * -(i+1) 2 + * (q + 2 ) <= y. (2) + * i + * -(i+1) + * If (2) is false, then q = q ; otherwise q = q + 2 . + * i+1 i i+1 i + * + * With some algebraic manipulation, it is not difficult to see + * that (2) is equivalent to + * -(i+1) + * s + 2 <= y (3) + * i i + * + * The advantage of (3) is that s and y can be computed by + * i i + * the following recurrence formula: + * if (3) is false + * + * s = s , y = y ; (4) + * i+1 i i+1 i + * + * otherwise, + * -i -(i+1) + * s = s + 2 , y = y - s - 2 (5) + * i+1 i i+1 i i + * + * One may easily use induction to prove (4) and (5). + * Note. Since the left hand side of (3) contain only i+2 bits, + * it does not necessary to do a full (53-bit) comparison + * in (3). + * 3. Final rounding + * After generating the 53 bits result, we compute one more bit. + * Together with the remainder, we can decide whether the + * result is exact, bigger than 1/2ulp, or less than 1/2ulp + * (it will never equal to 1/2ulp). + * The rounding mode can be detected by checking whether + * huge + tiny is equal to huge, and whether huge - tiny is + * equal to huge for some floating point number "huge" and "tiny". + * + * Special cases: + * sqrt(+-0) = +-0 ... exact + * sqrt(inf) = inf + * sqrt(-ve) = NaN ... with invalid signal + * sqrt(NaN) = NaN ... with invalid signal for signaling NaN + */ + +use core::f64; + +#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] +pub fn sqrt(x: f64) -> f64 { + // On wasm32 we know that LLVM's intrinsic will compile to an optimized + // `f64.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 { + f64::NAN + } else { + unsafe { ::core::intrinsics::sqrtf64(x) } + } + } + } + #[cfg(target_feature = "sse2")] + { + // Note: This path is unlikely since LLVM will usually have already + // optimized sqrt calls into hardware instructions if sse2 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_sd(x); + let m_sqrt = _mm_sqrt_pd(m); + _mm_cvtsd_f64(m_sqrt) + } + } + #[cfg(not(target_feature = "sse2"))] + { + use core::num::Wrapping; + + const TINY: f64 = 1.0e-300; + + let mut z: f64; + let sign: Wrapping<u32> = Wrapping(0x80000000); + let mut ix0: i32; + let mut s0: i32; + let mut q: i32; + let mut m: i32; + let mut t: i32; + let mut i: i32; + let mut r: Wrapping<u32>; + let mut t1: Wrapping<u32>; + let mut s1: Wrapping<u32>; + let mut ix1: Wrapping<u32>; + let mut q1: Wrapping<u32>; + + ix0 = (x.to_bits() >> 32) as i32; + ix1 = Wrapping(x.to_bits() as u32); + + /* take care of Inf and NaN */ + if (ix0 & 0x7ff00000) == 0x7ff00000 { + return x * x + x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf, sqrt(-inf)=sNaN */ + } + /* take care of zero */ + if ix0 <= 0 { + if ((ix0 & !(sign.0 as i32)) | ix1.0 as i32) == 0 { + return x; /* sqrt(+-0) = +-0 */ + } + if ix0 < 0 { + return (x - x) / (x - x); /* sqrt(-ve) = sNaN */ + } + } + /* normalize x */ + m = ix0 >> 20; + if m == 0 { + /* subnormal x */ + while ix0 == 0 { + m -= 21; + ix0 |= (ix1 >> 11).0 as i32; + ix1 <<= 21; + } + i = 0; + while (ix0 & 0x00100000) == 0 { + i += 1; + ix0 <<= 1; + } + m -= i - 1; + ix0 |= (ix1 >> (32 - i) as usize).0 as i32; + ix1 = ix1 << i as usize; + } + m -= 1023; /* unbias exponent */ + ix0 = (ix0 & 0x000fffff) | 0x00100000; + if (m & 1) == 1 { + /* odd m, double x to make it even */ + ix0 += ix0 + ((ix1 & sign) >> 31).0 as i32; + ix1 += ix1; + } + m >>= 1; /* m = [m/2] */ + + /* generate sqrt(x) bit by bit */ + ix0 += ix0 + ((ix1 & sign) >> 31).0 as i32; + ix1 += ix1; + q = 0; /* [q,q1] = sqrt(x) */ + q1 = Wrapping(0); + s0 = 0; + s1 = Wrapping(0); + r = Wrapping(0x00200000); /* r = moving bit from right to left */ + + while r != Wrapping(0) { + t = s0 + r.0 as i32; + if t <= ix0 { + s0 = t + r.0 as i32; + ix0 -= t; + q += r.0 as i32; + } + ix0 += ix0 + ((ix1 & sign) >> 31).0 as i32; + ix1 += ix1; + r >>= 1; + } + + r = sign; + while r != Wrapping(0) { + t1 = s1 + r; + t = s0; + if t < ix0 || (t == ix0 && t1 <= ix1) { + s1 = t1 + r; + if (t1 & sign) == sign && (s1 & sign) == Wrapping(0) { + s0 += 1; + } + ix0 -= t; + if ix1 < t1 { + ix0 -= 1; + } + ix1 -= t1; + q1 += r; + } + ix0 += ix0 + ((ix1 & sign) >> 31).0 as i32; + ix1 += ix1; + r >>= 1; + } + + /* use floating add to find out rounding direction */ + if (ix0 as u32 | ix1.0) != 0 { + z = 1.0 - TINY; /* raise inexact flag */ + if z >= 1.0 { + z = 1.0 + TINY; + if q1.0 == 0xffffffff { + q1 = Wrapping(0); + q += 1; + } else if z > 1.0 { + if q1.0 == 0xfffffffe { + q += 1; + } + q1 += Wrapping(2); + } else { + q1 += q1 & Wrapping(1); + } + } + } + ix0 = (q >> 1) + 0x3fe00000; + ix1 = q1 >> 1; + if (q & 1) == 1 { + ix1 |= sign; + } + ix0 += m << 20; + f64::from_bits((ix0 as u64) << 32 | ix1.0 as u64) + } +} + +#[cfg(test)] +mod tests { + use super::*; + use core::f64::*; + + #[test] + fn sanity_check() { + assert_eq!(sqrt(100.0), 10.0); + assert_eq!(sqrt(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!(sqrt(-1.0).is_nan()); + assert!(sqrt(NAN).is_nan()); + for f in [0.0, -0.0, INFINITY].iter().copied() { + assert_eq!(sqrt(f), f); + } + } +} |