104 lines
2.4 KiB
C
104 lines
2.4 KiB
C
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/* @(#)s_frexp.c 5.1 93/09/24 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/*
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FUNCTION
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<<frexp>>, <<frexpf>>---split floating-point number
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INDEX
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frexp
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INDEX
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frexpf
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SYNOPSIS
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#include <math.h>
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double frexp(double <[val]>, int *<[exp]>);
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float frexpf(float <[val]>, int *<[exp]>);
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DESCRIPTION
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All nonzero, normal numbers can be described as <[m]> * 2**<[p]>.
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<<frexp>> represents the double <[val]> as a mantissa <[m]>
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and a power of two <[p]>. The resulting mantissa will always
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be greater than or equal to <<0.5>>, and less than <<1.0>> (as
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long as <[val]> is nonzero). The power of two will be stored
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in <<*>><[exp]>.
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@ifnottex
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<[m]> and <[p]> are calculated so that
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<[val]> is <[m]> times <<2>> to the power <[p]>.
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@end ifnottex
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@tex
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<[m]> and <[p]> are calculated so that
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$ val = m \times 2^p $.
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@end tex
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<<frexpf>> is identical, other than taking and returning
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floats rather than doubles.
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RETURNS
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<<frexp>> returns the mantissa <[m]>. If <[val]> is <<0>>, infinity,
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or Nan, <<frexp>> will set <<*>><[exp]> to <<0>> and return <[val]>.
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PORTABILITY
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<<frexp>> is ANSI.
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<<frexpf>> is an extension.
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*/
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/*
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* for non-zero x
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* x = frexp(arg,&exp);
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* return a double fp quantity x such that 0.5 <= |x| <1.0
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* and the corresponding binary exponent "exp". That is
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* arg = x*2^exp.
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* If arg is inf, 0.0, or NaN, then frexp(arg,&exp) returns arg
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* with *exp=0.
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*/
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#include "fdlibm.h"
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#ifndef _DOUBLE_IS_32BITS
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#ifdef __STDC__
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static const double
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#else
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static double
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#endif
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two54 = 1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */
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#ifdef __STDC__
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double frexp(double x, int *eptr)
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#else
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double frexp(x, eptr)
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double x; int *eptr;
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#endif
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{
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__int32_t hx, ix, lx;
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EXTRACT_WORDS(hx,lx,x);
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ix = 0x7fffffff&hx;
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*eptr = 0;
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if(ix>=0x7ff00000||((ix|lx)==0)) return x; /* 0,inf,nan */
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if (ix<0x00100000) { /* subnormal */
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x *= two54;
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GET_HIGH_WORD(hx,x);
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ix = hx&0x7fffffff;
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*eptr = -54;
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}
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*eptr += (ix>>20)-1022;
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hx = (hx&0x800fffff)|0x3fe00000;
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SET_HIGH_WORD(x,hx);
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return x;
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}
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#endif /* _DOUBLE_IS_32BITS */
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