1 /* @(#)s_nextafter.c 5.1 93/09/24 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13 #include <sys/cdefs.h> 14 /* 15 * We assume that a long double has a 15-bit exponent. On systems 16 * where long double is the same as double, nexttoward() is an alias 17 * for nextafter(), so we don't use this routine. 18 */ 19 20 #include <float.h> 21 22 #include "fpmath.h" 23 #include "math.h" 24 #include "math_private.h" 25 26 #if LDBL_MAX_EXP != 0x4000 27 #error "Unsupported long double format" 28 #endif 29 30 double 31 nexttoward(double x, long double y) 32 { 33 union IEEEl2bits uy; 34 volatile double t; 35 int32_t hx,ix; 36 u_int32_t lx; 37 38 EXTRACT_WORDS(hx,lx,x); 39 ix = hx&0x7fffffff; /* |x| */ 40 uy.e = y; 41 42 if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) || 43 (uy.bits.exp == 0x7fff && 44 ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl) != 0)) 45 return x+y; /* x or y is nan */ 46 if(x==y) return (double)y; /* x=y, return y */ 47 if(x==0.0) { 48 INSERT_WORDS(x,uy.bits.sign<<31,1); /* return +-minsubnormal */ 49 t = x*x; 50 if(t==x) return t; else return x; /* raise underflow flag */ 51 } 52 if(hx>0.0 ^ x < y) { /* x -= ulp */ 53 if(lx==0) hx -= 1; 54 lx -= 1; 55 } else { /* x += ulp */ 56 lx += 1; 57 if(lx==0) hx += 1; 58 } 59 ix = hx&0x7ff00000; 60 if(ix>=0x7ff00000) return x+x; /* overflow */ 61 if(ix<0x00100000) { /* underflow */ 62 t = x*x; 63 if(t!=x) { /* raise underflow flag */ 64 INSERT_WORDS(x,hx,lx); 65 return x; 66 } 67 } 68 INSERT_WORDS(x,hx,lx); 69 return x; 70 } 71