1 | /* 2009 for Newlib: Sun's sf_ilogb.c converted to be sf_logb.c. */ |
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2 | /* |
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3 | * ==================================================== |
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4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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5 | * |
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6 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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7 | * Permission to use, copy, modify, and distribute this |
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8 | * software is freely granted, provided that this notice |
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9 | * is preserved. |
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10 | * ==================================================== |
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11 | */ |
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12 | |
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13 | /* float logb(float x) |
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14 | * return the binary exponent of non-zero x |
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15 | * logbf(0) = -inf, raise divide-by-zero floating point exception |
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16 | * logbf(+inf|-inf) = +inf (no signal is raised) |
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17 | * logbf(NaN) = NaN (no signal is raised) |
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18 | * Per C99 recommendation, a NaN argument is returned unchanged. |
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19 | */ |
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20 | |
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21 | #include "fdlibm.h" |
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22 | |
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23 | float |
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24 | #ifdef __STDC__ |
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25 | logbf(float x) |
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26 | #else |
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27 | logbf(x) |
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28 | float x; |
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29 | #endif |
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30 | { |
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31 | __int32_t hx,ix; |
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32 | |
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33 | GET_FLOAT_WORD(hx,x); |
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34 | hx &= 0x7fffffff; |
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35 | if(FLT_UWORD_IS_ZERO(hx)) { |
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36 | float xx; |
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37 | /* arg==0: return -inf and raise divide-by-zero exception */ |
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38 | SET_FLOAT_WORD(xx,hx); /* +0.0 */ |
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39 | return -1./xx; /* logbf(0) = -inf */ |
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40 | } |
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41 | if(FLT_UWORD_IS_SUBNORMAL(hx)) { |
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42 | for (ix = -126,hx<<=8; hx>0; hx<<=1) ix -=1; |
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43 | return (float) ix; |
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44 | } |
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45 | else if (FLT_UWORD_IS_INFINITE(hx)) return HUGE_VALF; /* x==+|-inf */ |
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46 | else if (FLT_UWORD_IS_NAN(hx)) return x; |
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47 | else return (float) ((hx>>23)-127); |
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48 | } |
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49 | |
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50 | #ifdef _DOUBLE_IS_32BITS |
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51 | |
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52 | #ifdef __STDC__ |
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53 | double logb(double x) |
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54 | #else |
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55 | double logb(x) |
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56 | double x; |
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57 | #endif |
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58 | { |
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59 | return (double) logbf((float) x); |
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60 | } |
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61 | |
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62 | #endif /* defined(_DOUBLE_IS_32BITS) */ |
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