mirror of
https://github.com/jart/cosmopolitan.git
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125 lines
4.6 KiB
C
125 lines
4.6 KiB
C
/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8 -*-│
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│vi: set et ft=c ts=8 tw=8 fenc=utf-8 :vi│
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╚──────────────────────────────────────────────────────────────────────────────╝
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│ │
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│ Musl Libc │
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│ Copyright © 2005-2014 Rich Felker, et al. │
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│ │
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│ Permission is hereby granted, free of charge, to any person obtaining │
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│ a copy of this software and associated documentation files (the │
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│ "Software"), to deal in the Software without restriction, including │
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│ without limitation the rights to use, copy, modify, merge, publish, │
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│ distribute, sublicense, and/or sell copies of the Software, and to │
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│ permit persons to whom the Software is furnished to do so, subject to │
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│ the following conditions: │
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│ │
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│ The above copyright notice and this permission notice shall be │
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│ included in all copies or substantial portions of the Software. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, │
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│ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF │
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│ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. │
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│ IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY │
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│ CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, │
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│ TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE │
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│ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. │
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│ │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/intrin/likely.h"
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#include "libc/math.h"
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#include "libc/tinymath/internal.h"
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asm(".ident\t\"\\n\\n\
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Musl libc (MIT License)\\n\
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Copyright 2005-2014 Rich Felker, et. al.\"");
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asm(".include \"libc/disclaimer.inc\"");
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// clang-format off
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#define FENV_SUPPORT 1
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static inline uint32_t mul32(uint32_t a, uint32_t b)
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{
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return (uint64_t)a*b >> 32;
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}
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/* see sqrt.c for more detailed comments. */
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float sqrtf(float x)
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{
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#ifdef __x86__
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float res;
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asm("sqrtss\t%1,%0" : "=x"(res) : "x"(x));
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return res;
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#else
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uint32_t ix, m, m1, m0, even, ey;
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ix = asuint(x);
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if (UNLIKELY(ix - 0x00800000 >= 0x7f800000 - 0x00800000)) {
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/* x < 0x1p-126 or inf or nan. */
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if (ix * 2 == 0)
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return x;
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if (ix == 0x7f800000)
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return x;
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if (ix > 0x7f800000)
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return __math_invalidf(x);
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/* x is subnormal, normalize it. */
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ix = asuint(x * 0x1p23f);
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ix -= 23 << 23;
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}
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/* x = 4^e m; with int e and m in [1, 4). */
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even = ix & 0x00800000;
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m1 = (ix << 8) | 0x80000000;
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m0 = (ix << 7) & 0x7fffffff;
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m = even ? m0 : m1;
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/* 2^e is the exponent part of the return value. */
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ey = ix >> 1;
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ey += 0x3f800000 >> 1;
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ey &= 0x7f800000;
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/* compute r ~ 1/sqrt(m), s ~ sqrt(m) with 2 goldschmidt iterations. */
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static const uint32_t three = 0xc0000000;
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uint32_t r, s, d, u, i;
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i = (ix >> 17) % 128;
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r = (uint32_t)__rsqrt_tab[i] << 16;
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/* |r*sqrt(m) - 1| < 0x1p-8 */
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s = mul32(m, r);
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/* |s/sqrt(m) - 1| < 0x1p-8 */
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d = mul32(s, r);
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u = three - d;
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r = mul32(r, u) << 1;
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/* |r*sqrt(m) - 1| < 0x1.7bp-16 */
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s = mul32(s, u) << 1;
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/* |s/sqrt(m) - 1| < 0x1.7bp-16 */
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d = mul32(s, r);
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u = three - d;
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s = mul32(s, u);
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/* -0x1.03p-28 < s/sqrt(m) - 1 < 0x1.fp-31 */
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s = (s - 1)>>6;
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/* s < sqrt(m) < s + 0x1.08p-23 */
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/* compute nearest rounded result. */
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uint32_t d0, d1, d2;
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float y, t;
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d0 = (m << 16) - s*s;
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d1 = s - d0;
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d2 = d1 + s + 1;
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s += d1 >> 31;
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s &= 0x007fffff;
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s |= ey;
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y = asfloat(s);
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if (FENV_SUPPORT) {
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/* handle rounding and inexact exception. */
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uint32_t tiny = UNLIKELY(d2==0) ? 0 : 0x01000000;
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tiny |= (d1^d2) & 0x80000000;
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t = asfloat(tiny);
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y = eval_as_float(y + t);
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}
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return y;
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#endif
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}
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