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| 2 | /* @(#)s_frexp.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 | <<frexp>>, <<frexpf>>---split floating-point number |
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| 17 | INDEX |
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| 18 | frexp |
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| 19 | INDEX |
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| 20 | frexpf |
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| 21 | |
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| 22 | SYNOPSIS |
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| 23 | #include <math.h> |
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| 24 | double frexp(double <[val]>, int *<[exp]>); |
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| 25 | float frexpf(float <[val]>, int *<[exp]>); |
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| 26 | |
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| 27 | DESCRIPTION |
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| 28 | All nonzero, normal numbers can be described as <[m]> * 2**<[p]>. |
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| 29 | <<frexp>> represents the double <[val]> as a mantissa <[m]> |
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| 30 | and a power of two <[p]>. The resulting mantissa will always |
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| 31 | be greater than or equal to <<0.5>>, and less than <<1.0>> (as |
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| 32 | long as <[val]> is nonzero). The power of two will be stored |
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| 33 | in <<*>><[exp]>. |
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| 34 | |
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| 35 | @ifnottex |
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| 36 | <[m]> and <[p]> are calculated so that |
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| 37 | <[val]> is <[m]> times <<2>> to the power <[p]>. |
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| 38 | @end ifnottex |
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| 39 | @tex |
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| 40 | <[m]> and <[p]> are calculated so that |
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| 41 | $ val = m \times 2^p $. |
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| 42 | @end tex |
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| 43 | |
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| 44 | <<frexpf>> is identical, other than taking and returning |
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| 45 | floats rather than doubles. |
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| 46 | |
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| 47 | RETURNS |
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| 48 | <<frexp>> returns the mantissa <[m]>. If <[val]> is <<0>>, infinity, |
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| 49 | or Nan, <<frexp>> will set <<*>><[exp]> to <<0>> and return <[val]>. |
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| 50 | |
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| 51 | PORTABILITY |
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| 52 | <<frexp>> is ANSI. |
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| 53 | <<frexpf>> is an extension. |
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| 54 | |
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| 55 | |
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| 56 | */ |
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| 57 | |
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| 58 | /* |
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| 59 | * for non-zero x |
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| 60 | * x = frexp(arg,&exp); |
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| 61 | * return a double fp quantity x such that 0.5 <= |x| <1.0 |
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| 62 | * and the corresponding binary exponent "exp". That is |
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| 63 | * arg = x*2^exp. |
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| 64 | * If arg is inf, 0.0, or NaN, then frexp(arg,&exp) returns arg |
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| 65 | * with *exp=0. |
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| 66 | */ |
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| 67 | |
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| 68 | #include "fdlibm.h" |
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| 69 | |
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| 70 | #ifndef _DOUBLE_IS_32BITS |
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| 71 | |
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| 72 | #ifdef __STDC__ |
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| 73 | static const double |
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| 74 | #else |
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| 75 | static double |
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| 76 | #endif |
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| 77 | two54 = 1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */ |
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| 78 | |
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| 79 | #ifdef __STDC__ |
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| 80 | double frexp(double x, int *eptr) |
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| 81 | #else |
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| 82 | double frexp(x, eptr) |
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| 83 | double x; int *eptr; |
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| 84 | #endif |
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| 85 | { |
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| 86 | __int32_t hx, ix, lx; |
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| 87 | EXTRACT_WORDS(hx,lx,x); |
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| 88 | ix = 0x7fffffff&hx; |
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| 89 | *eptr = 0; |
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| 90 | if(ix>=0x7ff00000||((ix|lx)==0)) return x; /* 0,inf,nan */ |
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| 91 | if (ix<0x00100000) { /* subnormal */ |
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| 92 | x *= two54; |
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| 93 | GET_HIGH_WORD(hx,x); |
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| 94 | ix = hx&0x7fffffff; |
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| 95 | *eptr = -54; |
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| 96 | } |
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| 97 | *eptr += (ix>>20)-1022; |
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| 98 | hx = (hx&0x800fffff)|0x3fe00000; |
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| 99 | SET_HIGH_WORD(x,hx); |
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| 100 | return x; |
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| 101 | } |
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| 102 | |
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| 103 | #endif /* _DOUBLE_IS_32BITS */ |
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