| 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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