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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