112 lines
2.3 KiB
C
112 lines
2.3 KiB
C
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/* @(#)z_frexp.c 1.0 98/08/13 */
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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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ANSI_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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TRAD_SYNOPSIS
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#include <math.h>
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double frexp(<[val]>, <[exp]>)
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double <[val]>;
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int *<[exp]>;
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float frexpf(<[val]>, <[exp]>)
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float <[val]>;
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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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* frexp
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*
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* Input:
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* d - floating point value
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* exp - exponent value
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*
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* Output:
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* A floating point value in the range [0.5, 1).
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*
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* Description:
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* This routine breaks a floating point value into a number f and
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* an exponent exp such that d = f * 2 ^ exp.
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*
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*****************************************************************/
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#include "fdlibm.h"
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#include "zmath.h"
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#ifndef _DOUBLE_IS_32BITS
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double frexp (double d, int *exp)
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{
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double f;
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__uint32_t hd, ld, hf, lf;
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/* Check for special values. */
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switch (numtest (d))
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{
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case NAN:
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case INF:
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errno = EDOM;
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case 0:
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*exp = 0;
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return (d);
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}
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EXTRACT_WORDS (hd, ld, d);
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/* Get the exponent. */
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*exp = ((hd & 0x7ff00000) >> 20) - 1022;
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/* Get the mantissa. */
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lf = ld;
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hf = hd & 0x800fffff;
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hf |= 0x3fe00000;
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INSERT_WORDS (f, hf, lf);
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return (f);
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}
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#endif /* _DOUBLE_IS_32BITS */
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