1 | /* ef_log10.c -- float version of e_log10.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 | #ifdef __STDC__ |
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19 | static const float |
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20 | #else |
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21 | static float |
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22 | #endif |
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23 | two25 = 3.3554432000e+07, /* 0x4c000000 */ |
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24 | ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */ |
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25 | log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ |
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26 | log10_2lo = 7.9034151668e-07; /* 0x355427db */ |
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27 | |
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28 | #ifdef __STDC__ |
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29 | static const float zero = 0.0; |
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30 | #else |
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31 | static float zero = 0.0; |
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32 | #endif |
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33 | |
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34 | #ifdef __STDC__ |
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35 | float __ieee754_log10f(float x) |
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36 | #else |
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37 | float __ieee754_log10f(x) |
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38 | float x; |
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39 | #endif |
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40 | { |
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41 | float y,z; |
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42 | __int32_t i,k,hx; |
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43 | |
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44 | GET_FLOAT_WORD(hx,x); |
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45 | |
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46 | k=0; |
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47 | if (FLT_UWORD_IS_ZERO(hx&0x7fffffff)) |
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48 | return -two25/zero; /* log(+-0)=-inf */ |
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49 | if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ |
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50 | if (!FLT_UWORD_IS_FINITE(hx)) return x+x; |
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51 | if (FLT_UWORD_IS_SUBNORMAL(hx)) { |
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52 | k -= 25; x *= two25; /* subnormal number, scale up x */ |
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53 | GET_FLOAT_WORD(hx,x); |
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54 | } |
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55 | k += (hx>>23)-127; |
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56 | i = ((__uint32_t)k&0x80000000)>>31; |
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57 | hx = (hx&0x007fffff)|((0x7f-i)<<23); |
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58 | y = (float)(k+i); |
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59 | SET_FLOAT_WORD(x,hx); |
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60 | z = y*log10_2lo + ivln10*__ieee754_logf(x); |
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61 | return z+y*log10_2hi; |
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62 | } |
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