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| 4349 | Serge | 1 | /* 2009 for Newlib: Sun's s_ilogb.c converted to be s_logb.c. */ |
| 2 | /* @(#)s_ilogb.c 5.1 93/09/24 */ |
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| 3 | /* |
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| 4 | * ==================================================== |
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| 5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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| 6 | * |
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| 7 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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| 8 | * Permission to use, copy, modify, and distribute this |
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| 9 | * software is freely granted, provided that this notice |
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| 10 | * is preserved. |
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| 11 | * ==================================================== |
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| 12 | */ |
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| 13 | /* |
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| 14 | FUNCTION |
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| 15 | < |
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| 16 | INDEX |
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| 17 | logb |
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| 18 | INDEX |
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| 19 | logbf |
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| 20 | |||
| 21 | ANSI_SYNOPSIS |
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| 22 | #include |
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| 23 | double logb(double <[x]>); |
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| 24 | float logbf(float <[x]>); |
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| 25 | |||
| 26 | DESCRIPTION |
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| 27 | The < |
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| 28 | in floating-point format. If <[x]> is subnormal it is treated as though it were |
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| 29 | normalized; thus, for positive finite <[x]>, |
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| 30 | @ifnottex |
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| 31 | 1 <= (<[x]> * FLT_RADIX to the power (-logb(<[x]>))) < FLT_RADIX. |
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| 32 | @end ifnottex |
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| 33 | @tex |
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| 34 | $1 \leq ( x \cdot FLT\_RADIX ^ {-logb(x)} ) < FLT\_RADIX$. |
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| 35 | @end tex |
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| 36 | A domain error may occur if the argument is zero. |
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| 37 | In this floating-point implementation, FLT_RADIX is 2. Which also means |
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| 38 | that for finite <[x]>, < |
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| 39 | |||
| 40 | All nonzero, normal numbers can be described as |
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| 41 | @ifnottex |
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| 42 | <[m]> * 2**<[p]>, where 1.0 <= <[m]> < 2.0. |
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| 43 | @end ifnottex |
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| 44 | @tex |
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| 45 | $m \cdot 2^p$, where $1.0 \leq m < 2.0$. |
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| 46 | @end tex |
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| 47 | The < |
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| 48 | The < |
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| 49 | returning <[m]> adjusted to the interval [.5, 1) or 0, and <[p]>+1. |
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| 50 | |||
| 51 | RETURNS |
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| 52 | @comment Formatting note: "$@" forces a new line |
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| 53 | When <[x]> is:@* |
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| 54 | +inf or -inf, +inf is returned;@* |
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| 55 | NaN, NaN is returned;@* |
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| 56 | 0, -inf is returned, and the divide-by-zero exception is raised;@* |
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| 57 | otherwise, the < |
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| 58 | |||
| 59 | PORTABILITY |
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| 60 | ANSI C, POSIX |
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| 61 | |||
| 62 | SEEALSO |
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| 63 | frexp, ilogb |
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| 64 | */ |
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| 65 | |||
| 66 | /* double logb(double x) |
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| 67 | * return the binary exponent of non-zero x |
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| 68 | * logb(0) = -inf, raise divide-by-zero floating point exception |
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| 69 | * logb(+inf|-inf) = +inf (no signal is raised) |
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| 70 | * logb(NaN) = NaN (no signal is raised) |
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| 71 | * Per C99 recommendation, a NaN argument is returned unchanged. |
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| 72 | */ |
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| 73 | |||
| 74 | #include "fdlibm.h" |
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| 75 | |||
| 76 | #ifndef _DOUBLE_IS_32BITS |
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| 77 | |||
| 78 | double |
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| 79 | #ifdef __STDC__ |
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| 80 | logb(double x) |
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| 81 | #else |
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| 82 | logb(x) |
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| 83 | double x; |
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| 84 | #endif |
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| 85 | { |
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| 86 | __int32_t hx,lx,ix; |
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| 87 | |||
| 88 | EXTRACT_WORDS(hx,lx,x); |
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| 89 | hx &= 0x7fffffff; /* high |x| */ |
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| 90 | if(hx<0x00100000) { /* 0 or subnormal */ |
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| 91 | if((hx|lx)==0) { |
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| 92 | double xx; |
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| 93 | /* arg==0: return -inf and raise divide-by-zero exception */ |
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| 94 | INSERT_WORDS(xx,hx,lx); /* +0.0 */ |
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| 95 | return -1./xx; /* logb(0) = -inf */ |
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| 96 | } |
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| 97 | else /* subnormal x */ |
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| 98 | if(hx==0) { |
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| 99 | for (ix = -1043; lx>0; lx<<=1) ix -=1; |
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| 100 | } else { |
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| 101 | for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; |
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| 102 | } |
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| 103 | return (double) ix; |
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| 104 | } |
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| 105 | else if (hx<0x7ff00000) return (hx>>20)-1023; /* normal # */ |
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| 106 | else if (hx>0x7ff00000 || lx) return x; /* x==NaN */ |
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| 107 | else return HUGE_VAL; /* x==inf (+ or -) */ |
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| 108 | } |
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| 109 | |||
| 110 | #endif /* _DOUBLE_IS_32BITS */ |