50 lines
1.2 KiB
C
50 lines
1.2 KiB
C
/* @(#)s_logb.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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#include "cdefs-compat.h"
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//__FBSDID("$FreeBSD: src/lib/msun/src/s_logb.c,v 1.12 2008/02/08 01:22:13 bde Exp $");
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/*
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* double logb(x)
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* IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
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* Use ilogb instead.
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*/
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#include <float.h>
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#include <openlibm_math.h>
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#include "math_private.h"
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static const double
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two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */
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OLM_DLLEXPORT double
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logb(double x)
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{
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int32_t lx,ix;
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EXTRACT_WORDS(ix,lx,x);
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ix &= 0x7fffffff; /* high |x| */
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if((ix|lx)==0) return -1.0/fabs(x);
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if(ix>=0x7ff00000) return x*x;
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if(ix<0x00100000) {
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x *= two54; /* convert subnormal x to normal */
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GET_HIGH_WORD(ix,x);
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ix &= 0x7fffffff;
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return (double) ((ix>>20)-1023-54);
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} else
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return (double) ((ix>>20)-1023);
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}
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#if (LDBL_MANT_DIG == 53)
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openlibm_weak_reference(logb, logbl);
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#endif
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