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| 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 | /* |
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| 15 | FUNCTION |
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| 16 | <<ilogb>>, <<ilogbf>>---get exponent of floating-point number |
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| 17 | INDEX |
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| 18 | ilogb |
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| 19 | INDEX |
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| 20 | ilogbf |
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| 21 | |
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| 22 | SYNOPSIS |
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| 23 | #include <math.h> |
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| 24 | int ilogb(double <[val]>); |
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| 25 | int ilogbf(float <[val]>); |
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| 26 | |
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| 27 | DESCRIPTION |
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| 28 | |
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| 29 | All nonzero, normal numbers can be described as <[m]> * |
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| 30 | 2**<[p]>. <<ilogb>> and <<ilogbf>> examine the argument |
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| 31 | <[val]>, and return <[p]>. The functions <<frexp>> and |
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| 32 | <<frexpf>> are similar to <<ilogb>> and <<ilogbf>>, but also |
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| 33 | return <[m]>. |
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| 34 | |
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| 35 | RETURNS |
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| 36 | |
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| 37 | <<ilogb>> and <<ilogbf>> return the power of two used to form the |
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| 38 | floating-point argument. |
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| 39 | If <[val]> is <<0>>, they return <<FP_ILOGB0>>. |
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| 40 | If <[val]> is infinite, they return <<INT_MAX>>. |
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| 41 | If <[val]> is NaN, they return <<FP_ILOGBNAN>>. |
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| 42 | (<<FP_ILOGB0>> and <<FP_ILOGBNAN>> are defined in math.h, but in turn are |
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| 43 | defined as INT_MIN or INT_MAX from limits.h. The value of FP_ILOGB0 may be |
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| 44 | either INT_MIN or -INT_MAX. The value of FP_ILOGBNAN may be either INT_MAX or |
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| 45 | INT_MIN.) |
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| 46 | |
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| 47 | @comment The bugs might not be worth noting, given the mass non-C99/POSIX |
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| 48 | @comment behavior of much of the Newlib math library. |
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| 49 | @comment BUGS |
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| 50 | @comment On errors, errno is not set per C99 and POSIX requirements even if |
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| 51 | @comment (math_errhandling & MATH_ERRNO) is non-zero. |
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| 52 | |
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| 53 | PORTABILITY |
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| 54 | C99, POSIX |
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| 55 | */ |
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| 56 | |
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| 57 | /* ilogb(double x) |
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| 58 | * return the binary exponent of non-zero x |
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| 59 | * ilogb(0) = 0x80000001 |
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| 60 | * ilogb(inf/NaN) = 0x7fffffff (no signal is raised) |
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| 61 | */ |
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| 62 | |
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| 63 | #include <limits.h> |
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| 64 | #include "fdlibm.h" |
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| 65 | |
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| 66 | #ifndef _DOUBLE_IS_32BITS |
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| 67 | |
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| 68 | #ifdef __STDC__ |
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| 69 | int ilogb(double x) |
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| 70 | #else |
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| 71 | int ilogb(x) |
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| 72 | double x; |
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| 73 | #endif |
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| 74 | { |
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| 75 | __int32_t hx,lx,ix; |
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| 76 | |
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| 77 | EXTRACT_WORDS(hx,lx,x); |
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| 78 | hx &= 0x7fffffff; |
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| 79 | if(hx<0x00100000) { |
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| 80 | if((hx|lx)==0) |
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| 81 | return FP_ILOGB0; /* ilogb(0) = special case error */ |
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| 82 | else /* subnormal x */ |
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| 83 | if(hx==0) { |
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| 84 | for (ix = -1043; lx>0; lx<<=1) ix -=1; |
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| 85 | } else { |
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| 86 | for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; |
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| 87 | } |
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| 88 | return ix; |
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| 89 | } |
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| 90 | else if (hx<0x7ff00000) return (hx>>20)-1023; |
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| 91 | #if FP_ILOGBNAN != INT_MAX |
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| 92 | else if (hx>0x7ff00000) return FP_ILOGBNAN; /* NAN */ |
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| 93 | #endif |
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| 94 | else return INT_MAX; /* infinite (or, possibly, NAN) */ |
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| 95 | } |
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| 96 | |
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| 97 | #endif /* _DOUBLE_IS_32BITS */ |
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