1 /* $NetBSD: s_nexttoward.c,v 1.1 2010/09/15 16:12:05 christos Exp $ */ 2 3 /* @(#)s_nextafter.c 5.1 93/09/24 */ 4 /* 5 * ==================================================== 6 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 7 * 8 * Developed at SunPro, a Sun Microsystems, Inc. business. 9 * Permission to use, copy, modify, and distribute this 10 * software is freely granted, provided that this notice 11 * is preserved. 12 * ==================================================== 13 */ 14 15 #include <sys/cdefs.h> 16 __RCSID("$NetBSD: s_nexttoward.c,v 1.1 2010/09/15 16:12:05 christos Exp $"); 17 18 /* 19 * We assume that a long double has a 15-bit exponent. On systems 20 * where long double is the same as double, nexttoward() is an alias 21 * for nextafter(), so we don't use this routine. 22 */ 23 #include <float.h> 24 25 #include <machine/ieee.h> 26 #include "math.h" 27 #include "math_private.h" 28 29 #if LDBL_MAX_EXP != 0x4000 30 #error "Unsupported long double format" 31 #endif 32 33 /* 34 * The nexttoward() function is equivalent to nextafter() function, 35 * except that the second parameter shall have type long double and 36 * the functions shall return y converted to the type of the function 37 * if x equals y. 38 * 39 * Special cases: XXX 40 */ 41 double 42 nexttoward(double x, long double y) 43 { 44 union ieee_ext_u uy; 45 volatile double t; 46 int32_t hx, ix; 47 uint32_t lx; 48 49 EXTRACT_WORDS(hx, lx, x); 50 ix = hx & 0x7fffffff; /* |x| */ 51 uy.extu_ld = y; 52 53 if (((ix >= 0x7ff00000) && ((ix - 0x7ff00000) | lx) != 0) || 54 (uy.extu_exp == 0x7fff && 55 ((uy.extu_frach & ~LDBL_NBIT) | uy.extu_fracl) != 0)) 56 return x+y; /* x or y is nan */ 57 58 if (x == y) 59 return (double)y; /* x=y, return y */ 60 61 if (x == 0.0) { 62 INSERT_WORDS(x, uy.extu_sign<<31, 1); /* return +-minsubnormal */ 63 t = x*x; 64 if (t == x) 65 return t; 66 else 67 return x; /* raise underflow flag */ 68 } 69 70 if ((hx > 0.0) ^ (x < y)) { /* x -= ulp */ 71 if (lx == 0) hx -= 1; 72 lx -= 1; 73 } else { /* x += ulp */ 74 lx += 1; 75 if (lx == 0) hx += 1; 76 } 77 ix = hx & 0x7ff00000; 78 if (ix >= 0x7ff00000) return x+x; /* overflow */ 79 if (ix < 0x00100000) { /* underflow */ 80 t = x*x; 81 if (t != x) { /* raise underflow flag */ 82 INSERT_WORDS(y, hx, lx); 83 return y; 84 } 85 } 86 INSERT_WORDS(x, hx, lx); 87 88 return x; 89 } 90