64 lines
1.5 KiB
C
64 lines
1.5 KiB
C
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/* @(#)s_ilogb.c 5.1 93/09/24 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#if defined(LIBM_SCCS) && !defined(lint)
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static char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $";
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#endif
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/* ilogb(double x)
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* return the binary exponent of non-zero x
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* ilogb(0) = FP_ILOGB0
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* ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
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* ilogb(+-Inf) = INT_MAX (no signal is raised)
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*/
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#include <limits.h>
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#include <math.h>
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#include <math_private.h>
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int
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__ieee754_ilogb (double x)
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{
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int32_t hx, lx, ix;
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GET_HIGH_WORD (hx, x);
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hx &= 0x7fffffff;
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if (hx < 0x00100000)
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{
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GET_LOW_WORD (lx, x);
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if ((hx | lx) == 0)
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return FP_ILOGB0; /* ilogb(0) = FP_ILOGB0 */
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else /* subnormal x */
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if (hx == 0)
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{
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for (ix = -1043; lx > 0; lx <<= 1)
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ix -= 1;
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}
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else
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{
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for (ix = -1022, hx <<= 11; hx > 0; hx <<= 1)
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ix -= 1;
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}
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return ix;
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}
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else if (hx < 0x7ff00000)
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return (hx >> 20) - 1023;
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else if (FP_ILOGBNAN != INT_MAX)
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{
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/* ISO C99 requires ilogb(+-Inf) == INT_MAX. */
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GET_LOW_WORD (lx, x);
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if (((hx ^ 0x7ff00000) | lx) == 0)
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return INT_MAX;
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}
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return FP_ILOGBNAN;
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}
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