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/* @(#)s_logb.c 5.1 93/09/24 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
/*
* double logb(x)
* IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
* Use ilogb instead.
*/
#include <float.h>
#include "math.h"
#include "math_private.h"
static const double
two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */
double
logb(double x)
{
int32_t lx,ix;
EXTRACT_WORDS(ix,lx,x);
ix &= 0x7fffffff; /* high |x| */
if((ix|lx)==0) return -1.0/fabs(x);
if(ix>=0x7ff00000) return x*x;
if(ix<0x00100000) {
x *= two54; /* convert subnormal x to normal */
GET_HIGH_WORD(ix,x);
ix &= 0x7fffffff;
return (double) ((ix>>20)-1023-54);
} else
return (double) ((ix>>20)-1023);
}
#if (LDBL_MANT_DIG == 53)
__weak_reference(logb, logbl);
#endif
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