Dawid Sobczak
2ae045cf8a
I pulled in the implementation of a few log functions from musl 0.8.7 because lua needed log2 to compile. Since lua needed only log2 I commented out the ones that didn't immediatly compile like log1p.c.
72 lines
1.9 KiB
C
72 lines
1.9 KiB
C
/* origin: FreeBSD /usr/src/lib/msun/src/e_log10f.c */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/*
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* See comments in log10.c.
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*/
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#include "math.h"
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#include "__log1pf.h"
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#include <stdint.h>
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static const float
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two25 = 3.3554432000e+07, /* 0x4c000000 */
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ivln10hi = 4.3432617188e-01, /* 0x3ede6000 */
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ivln10lo = -3.1689971365e-05, /* 0xb804ead9 */
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log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */
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log10_2lo = 7.9034151668e-07; /* 0x355427db */
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static const float zero = 0.0;
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float log10f(float x)
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{
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float f,hfsq,hi,lo,r,y;
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int32_t i,k,hx;
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GET_FLOAT_WORD(hx, x);
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k = 0;
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if (hx < 0x00800000) { /* x < 2**-126 */
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if ((hx&0x7fffffff) == 0)
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return -two25/zero; /* log(+-0)=-inf */
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if (hx < 0)
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return (x-x)/zero; /* log(-#) = NaN */
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/* subnormal number, scale up x */
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k -= 25;
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x *= two25;
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GET_FLOAT_WORD(hx, x);
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}
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if (hx >= 0x7f800000)
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return x+x;
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if (hx == 0x3f800000)
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return zero; /* log(1) = +0 */
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k += (hx>>23) - 127;
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hx &= 0x007fffff;
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i = (hx+(0x4afb0d))&0x800000;
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SET_FLOAT_WORD(x, hx|(i^0x3f800000)); /* normalize x or x/2 */
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k += i>>23;
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y = (float)k;
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f = x - 1.0f;
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hfsq = 0.5f * f * f;
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r = __log1pf(f);
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// FIXME
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// /* See log2f.c and log2.c for details. */
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// if (sizeof(float_t) > sizeof(float))
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// return (r - hfsq + f) * ((float_t)ivln10lo + ivln10hi) +
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// y * ((float_t)log10_2lo + log10_2hi);
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hi = f - hfsq;
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GET_FLOAT_WORD(hx, hi);
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SET_FLOAT_WORD(hi, hx&0xfffff000);
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lo = (f - hi) - hfsq + r;
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return y*log10_2lo + (lo+hi)*ivln10lo + lo*ivln10hi +
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hi*ivln10hi + y*log10_2hi;
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}
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