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/* @(#)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.
* ====================================================
*/
#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $";
#endif
/* ilogb(double x)
* return the binary exponent of non-zero x
* ilogb(0) = FP_ILOGB0
* ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
* ilogb(+-Inf) = INT_MAX (no signal is raised)
*/
#include <limits.h>
#include <math.h>
#include <math_private.h>
int
__ieee754_ilogb (double x)
{
int32_t hx, lx, ix;
GET_HIGH_WORD (hx, x);
hx &= 0x7fffffff;
if (hx < 0x00100000)
{
GET_LOW_WORD (lx, x);
if ((hx | lx) == 0)
return FP_ILOGB0; /* ilogb(0) = FP_ILOGB0 */
else /* subnormal x */
if (hx == 0)
{
for (ix = -1043; lx > 0; lx <<= 1)
ix -= 1;
}
else
{
for (ix = -1022, hx <<= 11; hx > 0; hx <<= 1)
ix -= 1;
}
return ix;
}
else if (hx < 0x7ff00000)
return (hx >> 20) - 1023;
else if (FP_ILOGBNAN != INT_MAX)
{
/* ISO C99 requires ilogb(+-Inf) == INT_MAX. */
GET_LOW_WORD (lx, x);
if (((hx ^ 0x7ff00000) | lx) == 0)
return INT_MAX;
}
return FP_ILOGBNAN;
}
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