| 1 | /* e_logf.c -- float version of e_log.c.
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| 2 | * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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| 3 | */
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| 4 |
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| 5 | /*
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| 6 | * ====================================================
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| 7 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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| 8 | *
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| 9 | * Developed at SunPro, a Sun Microsystems, Inc. business.
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| 10 | * Permission to use, copy, modify, and distribute this
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| 11 | * software is freely granted, provided that this notice
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| 12 | * is preserved.
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| 13 | * ====================================================
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| 14 | */
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| 15 |
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| 16 | #ifndef lint
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| 17 | static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_logf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $";
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| 18 | #endif
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| 19 |
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| 20 | #include "math.h"
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| 21 | #include "math_private.h"
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| 22 |
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| 23 | static const float
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| 24 | ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
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| 25 | ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */
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| 26 | two25 = 3.355443200e+07, /* 0x4c000000 */
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| 27 | Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
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| 28 | Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
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| 29 | Lg3 = 2.8571429849e-01, /* 3E924925 */
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| 30 | Lg4 = 2.2222198546e-01, /* 3E638E29 */
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| 31 | Lg5 = 1.8183572590e-01, /* 3E3A3325 */
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| 32 | Lg6 = 1.5313838422e-01, /* 3E1CD04F */
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| 33 | Lg7 = 1.4798198640e-01; /* 3E178897 */
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| 34 |
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| 35 | static const float zero = 0.0;
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| 36 |
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| 37 | float
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| 38 | __ieee754_logf(float x)
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| 39 | {
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| 40 | float hfsq,f,s,z,R,w,t1,t2,dk;
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| 41 | int32_t k,ix,i,j;
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| 42 |
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| 43 | GET_FLOAT_WORD(ix,x);
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| 44 |
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| 45 | k=0;
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| 46 | if (ix < 0x00800000) { /* x < 2**-126 */
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| 47 | if ((ix&0x7fffffff)==0)
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| 48 | return -two25/zero; /* log(+-0)=-inf */
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| 49 | if (ix<0) return (x-x)/zero; /* log(-#) = NaN */
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| 50 | k -= 25; x *= two25; /* subnormal number, scale up x */
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| 51 | GET_FLOAT_WORD(ix,x);
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| 52 | }
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| 53 | if (ix >= 0x7f800000) return x+x;
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| 54 | k += (ix>>23)-127;
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| 55 | ix &= 0x007fffff;
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| 56 | i = (ix+(0x95f64<<3))&0x800000;
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| 57 | SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
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| 58 | k += (i>>23);
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| 59 | f = x-(float)1.0;
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| 60 | if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
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| 61 | if(f==zero) if(k==0) return zero; else {dk=(float)k;
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| 62 | return dk*ln2_hi+dk*ln2_lo;}
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| 63 | R = f*f*((float)0.5-(float)0.33333333333333333*f);
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| 64 | if(k==0) return f-R; else {dk=(float)k;
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| 65 | return dk*ln2_hi-((R-dk*ln2_lo)-f);}
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| 66 | }
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| 67 | s = f/((float)2.0+f);
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| 68 | dk = (float)k;
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| 69 | z = s*s;
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| 70 | i = ix-(0x6147a<<3);
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| 71 | w = z*z;
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| 72 | j = (0x6b851<<3)-ix;
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| 73 | t1= w*(Lg2+w*(Lg4+w*Lg6));
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| 74 | t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
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| 75 | i |= j;
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| 76 | R = t2+t1;
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| 77 | if(i>0) {
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| 78 | hfsq=(float)0.5*f*f;
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| 79 | if(k==0) return f-(hfsq-s*(hfsq+R)); else
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| 80 | return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
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| 81 | } else {
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| 82 | if(k==0) return f-s*(f-R); else
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| 83 | return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
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| 84 | }
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| 85 | }
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