114 lines
2.1 KiB
C
114 lines
2.1 KiB
C
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/* @(#)z_ldexp.c 1.0 98/08/13 */
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/*
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FUNCTION
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<<ldexp>>, <<ldexpf>>---load exponent
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INDEX
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ldexp
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INDEX
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ldexpf
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SYNOPSIS
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#include <math.h>
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double ldexp(double <[val]>, int <[exp]>);
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float ldexpf(float <[val]>, int <[exp]>);
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DESCRIPTION
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<<ldexp>> calculates the value
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@ifnottex
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<[val]> times 2 to the power <[exp]>.
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@end ifnottex
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@tex
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$val\times 2^{exp}$.
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@end tex
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<<ldexpf>> is identical, save that it takes and returns <<float>>
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rather than <<double>> values.
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RETURNS
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<<ldexp>> returns the calculated value.
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Underflow and overflow both set <<errno>> to <<ERANGE>>.
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On underflow, <<ldexp>> and <<ldexpf>> return 0.0.
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On overflow, <<ldexp>> returns plus or minus <<HUGE_VAL>>.
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PORTABILITY
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<<ldexp>> is ANSI. <<ldexpf>> is an extension.
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*/
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/******************************************************************
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* ldexp
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*
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* Input:
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* d - a floating point value
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* e - an exponent value
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*
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* Output:
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* A floating point value f such that f = d * 2 ^ e.
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*
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* Description:
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* This function creates a floating point number f such that
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* f = d * 2 ^ e.
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*
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*****************************************************************/
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#include <float.h>
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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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#define DOUBLE_EXP_OFFS 1023
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double
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ldexp (double d,
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int e)
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{
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int exp;
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__uint32_t hd;
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GET_HIGH_WORD (hd, d);
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/* Check for special values and then scale d by e. */
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switch (numtest (d))
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{
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case NAN:
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errno = EDOM;
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break;
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case INF:
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errno = ERANGE;
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break;
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case 0:
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break;
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default:
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exp = (hd & 0x7ff00000) >> 20;
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exp += e;
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if (exp > DBL_MAX_EXP + DOUBLE_EXP_OFFS)
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{
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errno = ERANGE;
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d = z_infinity.d;
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}
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else if (exp < DBL_MIN_EXP + DOUBLE_EXP_OFFS)
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{
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errno = ERANGE;
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d = -z_infinity.d;
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}
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else
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{
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hd &= 0x800fffff;
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hd |= exp << 20;
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SET_HIGH_WORD (d, hd);
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}
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}
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return (d);
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}
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#endif /* _DOUBLE_IS_32BITS */
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