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https://git.planet-casio.com/Lephenixnoir/OpenLibm.git
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55 lines
1.3 KiB
C
55 lines
1.3 KiB
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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#include <sys/cdefs.h>
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/* __kernel_logf(x)
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* Return log(x) - (x-1) for x in ~[sqrt(2)/2, sqrt(2)].
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*/
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static const float
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/* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
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Lg1 = 0xaaaaaa.0p-24, /* 0.66666662693 */
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Lg2 = 0xccce13.0p-25, /* 0.40000972152 */
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Lg3 = 0x91e9ee.0p-25, /* 0.28498786688 */
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Lg4 = 0xf89e26.0p-26; /* 0.24279078841 */
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static inline float
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__kernel_logf(float x)
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{
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float hfsq,f,s,z,R,w,t1,t2;
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int32_t ix,i,j;
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GET_FLOAT_WORD(ix,x);
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f = x-(float)1.0;
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if((0x007fffff&(0x8000+ix))<0xc000) { /* -2**-9 <= f < 2**-9 */
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if(f==0.0) return 0.0;
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return f*f*((float)0.33333333333333333*f-(float)0.5);
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}
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s = f/((float)2.0+f);
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z = s*s;
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ix &= 0x007fffff;
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i = ix-(0x6147a<<3);
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w = z*z;
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j = (0x6b851<<3)-ix;
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t1= w*(Lg2+w*Lg4);
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t2= z*(Lg1+w*Lg3);
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i |= j;
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R = t2+t1;
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if(i>0) {
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hfsq=(float)0.5*f*f;
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return s*(hfsq+R) - hfsq;
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} else {
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return s*(R-f);
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}
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}
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