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90 lines
2.2 KiB
C
90 lines
2.2 KiB
C
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/* $NetBSD: s_nexttoward.c,v 1.1 2010/09/15 16:12:05 christos Exp $ */
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/* @(#)s_nextafter.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 <sys/cdefs.h>
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__RCSID("$NetBSD: s_nexttoward.c,v 1.1 2010/09/15 16:12:05 christos Exp $");
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/*
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* We assume that a long double has a 15-bit exponent. On systems
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* where long double is the same as double, nexttoward() is an alias
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* for nextafter(), so we don't use this routine.
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*/
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#include <float.h>
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#include <machine/ieee.h>
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#include "math.h"
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#include "math_private.h"
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#if LDBL_MAX_EXP != 0x4000
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#error "Unsupported long double format"
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#endif
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/*
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* The nexttoward() function is equivalent to nextafter() function,
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* except that the second parameter shall have type long double and
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* the functions shall return y converted to the type of the function
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* if x equals y.
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*
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* Special cases: XXX
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*/
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double
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nexttoward(double x, long double y)
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{
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union ieee_ext_u uy;
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volatile double t;
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int32_t hx, ix;
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uint32_t lx;
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EXTRACT_WORDS(hx, lx, x);
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ix = hx & 0x7fffffff; /* |x| */
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uy.extu_ld = y;
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if (((ix >= 0x7ff00000) && ((ix - 0x7ff00000) | lx) != 0) ||
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(uy.extu_exp == 0x7fff &&
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((uy.extu_frach & ~LDBL_NBIT) | uy.extu_fracl) != 0))
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return x+y; /* x or y is nan */
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if (x == y)
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return (double)y; /* x=y, return y */
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if (x == 0.0) {
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INSERT_WORDS(x, uy.extu_sign<<31, 1); /* return +-minsubnormal */
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t = x*x;
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if (t == x)
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return t;
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else
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return x; /* raise underflow flag */
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}
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if ((hx > 0.0) ^ (x < y)) { /* x -= ulp */
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if (lx == 0) hx -= 1;
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lx -= 1;
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} else { /* x += ulp */
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lx += 1;
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if (lx == 0) hx += 1;
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}
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ix = hx & 0x7ff00000;
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if (ix >= 0x7ff00000) return x+x; /* overflow */
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if (ix < 0x00100000) { /* underflow */
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t = x*x;
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if (t != x) { /* raise underflow flag */
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INSERT_WORDS(y, hx, lx);
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return y;
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}
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}
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INSERT_WORDS(x, hx, lx);
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return x;
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}
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