| 1 | /* ef_log.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 | #include "fdlibm.h" |
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| 17 | |
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| 18 | #if __OBSOLETE_MATH |
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| 19 | #ifdef __STDC__ |
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| 20 | static const float |
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| 21 | #else |
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| 22 | static float |
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| 23 | #endif |
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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 | #ifdef __STDC__ |
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| 36 | static const float zero = 0.0; |
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| 37 | #else |
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| 38 | static float zero = 0.0; |
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| 39 | #endif |
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| 40 | |
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| 41 | #ifdef __STDC__ |
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| 42 | float __ieee754_logf(float x) |
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| 43 | #else |
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| 44 | float __ieee754_logf(x) |
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| 45 | float x; |
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| 46 | #endif |
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| 47 | { |
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| 48 | float hfsq,f,s,z,R,w,t1,t2,dk; |
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| 49 | __int32_t k,ix,i,j; |
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| 50 | |
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| 51 | GET_FLOAT_WORD(ix,x); |
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| 52 | |
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| 53 | k=0; |
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| 54 | if (FLT_UWORD_IS_ZERO(ix&0x7fffffff)) |
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| 55 | return -two25/zero; /* log(+-0)=-inf */ |
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| 56 | if (ix<0) return (x-x)/zero; /* log(-#) = NaN */ |
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| 57 | if (!FLT_UWORD_IS_FINITE(ix)) return x+x; |
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| 58 | if (FLT_UWORD_IS_SUBNORMAL(ix)) { |
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| 59 | k -= 25; x *= two25; /* subnormal number, scale up x */ |
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| 60 | GET_FLOAT_WORD(ix,x); |
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| 61 | } |
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| 62 | k += (ix>>23)-127; |
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| 63 | ix &= 0x007fffff; |
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| 64 | i = (ix+(0x95f64<<3))&0x800000; |
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| 65 | SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */ |
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| 66 | k += (i>>23); |
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| 67 | f = x-(float)1.0; |
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| 68 | if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */ |
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| 69 | if(f==zero) { if(k==0) return zero; else {dk=(float)k; |
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| 70 | return dk*ln2_hi+dk*ln2_lo;}} |
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| 71 | R = f*f*((float)0.5-(float)0.33333333333333333*f); |
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| 72 | if(k==0) return f-R; else {dk=(float)k; |
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| 73 | return dk*ln2_hi-((R-dk*ln2_lo)-f);} |
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| 74 | } |
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| 75 | s = f/((float)2.0+f); |
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| 76 | dk = (float)k; |
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| 77 | z = s*s; |
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| 78 | i = ix-(0x6147a<<3); |
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| 79 | w = z*z; |
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| 80 | j = (0x6b851<<3)-ix; |
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| 81 | t1= w*(Lg2+w*(Lg4+w*Lg6)); |
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| 82 | t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7))); |
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| 83 | i |= j; |
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| 84 | R = t2+t1; |
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| 85 | if(i>0) { |
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| 86 | hfsq=(float)0.5*f*f; |
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| 87 | if(k==0) return f-(hfsq-s*(hfsq+R)); else |
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| 88 | return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f); |
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| 89 | } else { |
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| 90 | if(k==0) return f-s*(f-R); else |
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| 91 | return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f); |
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| 92 | } |
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| 93 | } |
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| 94 | #endif /* __OBSOLETE_MATH */ |
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