63 lines
1.6 KiB
C
63 lines
1.6 KiB
C
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/* ef_log10.c -- float version of e_log10.c.
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* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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*/
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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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#include "fdlibm.h"
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#ifdef __STDC__
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static const float
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#else
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static float
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#endif
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two25 = 3.3554432000e+07, /* 0x4c000000 */
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ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */
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log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */
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log10_2lo = 7.9034151668e-07; /* 0x355427db */
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#ifdef __STDC__
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static const float zero = 0.0;
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#else
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static float zero = 0.0;
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#endif
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#ifdef __STDC__
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float __ieee754_log10f(float x)
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#else
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float __ieee754_log10f(x)
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float x;
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#endif
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{
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float y,z;
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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) return (x-x)/zero; /* log(-#) = NaN */
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k -= 25; x *= two25; /* subnormal number, scale up x */
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GET_FLOAT_WORD(hx,x);
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}
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if (hx >= 0x7f800000) return x+x;
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k += (hx>>23)-127;
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i = ((__uint32_t)k&0x80000000)>>31;
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hx = (hx&0x007fffff)|((0x7f-i)<<23);
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y = (float)(k+i);
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SET_FLOAT_WORD(x,hx);
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z = y*log10_2lo + ivln10*__ieee754_logf(x);
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return z+y*log10_2hi;
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}
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