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/* $OpenBSD: s_logbl.c,v 1.1 2008/12/09 20:00:35 martynas Exp $ */
/*
* From: @(#)s_ilogb.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/types.h>
#include <machine/ieee.h>
#include <float.h>
#include <limits.h>
#include <math.h>
long double
logbl(long double x)
{
union {
long double e;
struct ieee_ext bits;
} u;
unsigned long m;
int b;
u.e = x;
if (u.bits.ext_exp == 0) {
if ((u.bits.ext_fracl
#ifdef EXT_FRACLMBITS
| u.bits.ext_fraclm
#endif /* EXT_FRACLMBITS */
#ifdef EXT_FRACHMBITS
| u.bits.ext_frachm
#endif /* EXT_FRACHMBITS */
| u.bits.ext_frach) == 0) { /* x == 0 */
u.bits.ext_sign = 1;
return (1.0L / u.e);
}
/* denormalized */
if (u.bits.ext_frach == 0
#ifdef EXT_FRACHMBITS
&& u.bits.ext_frachm == 0
#endif
) {
m = 1lu << (EXT_FRACLBITS - 1);
for (b = EXT_FRACHBITS; !(u.bits.ext_fracl & m); m >>= 1)
b++;
#if defined(EXT_FRACHMBITS) && defined(EXT_FRACLMBITS)
m = 1lu << (EXT_FRACLMBITS - 1);
for (b += EXT_FRACHMBITS; !(u.bits.ext_fraclm & m);
m >>= 1)
b++;
#endif /* defined(EXT_FRACHMBITS) && defined(EXT_FRACLMBITS) */
} else {
m = 1lu << (EXT_FRACHBITS - 1);
for (b = 0; !(u.bits.ext_frach & m); m >>= 1)
b++;
#ifdef EXT_FRACHMBITS
m = 1lu << (EXT_FRACHMBITS - 1);
for (; !(u.bits.ext_frachm & m); m >>= 1)
b++;
#endif /* EXT_FRACHMBITS */
}
#ifdef EXT_IMPLICIT_NBIT
b++;
#endif
return ((long double)(LDBL_MIN_EXP - b - 1));
}
if (u.bits.ext_exp < (LDBL_MAX_EXP << 1) - 1) /* normal */
return ((long double)(u.bits.ext_exp - LDBL_MAX_EXP + 1));
else /* +/- inf or nan */
return (x * x);
}
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