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/* e_log10f.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 "math.h" |
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#include "math_private.h" |
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static const float |
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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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static const float zero = 0.0; |
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float |
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log10f(float x) |
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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 = ((u_int32_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*logf(x); |
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return z+y*log10_2hi; |
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} |