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 #ifndef lint 14 static char rcsid[] = "$FreeBSD$"; 15 #endif 16 17 /* 18 * We assume that a long double has a 15-bit exponent. On systems 19 * where long double is the same as double, nexttoward() is an alias 20 * for nextafter(), so we don't use this routine. 21 */ 22 23 #include <float.h> 24 25 #include "fpmath.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 double 34 nexttoward(double x, long double y) 35 { 36 union IEEEl2bits uy; 37 volatile double t; 38 int32_t hx,ix; 39 u_int32_t lx; 40 41 EXTRACT_WORDS(hx,lx,x); 42 ix = hx&0x7fffffff; /* |x| */ 43 uy.e = y; 44 45 if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) || 46 (uy.bits.exp == 0x7fff && 47 ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl) != 0)) 48 return x+y; /* x or y is nan */ 49 if(x==y) return (double)y; /* x=y, return y */ 50 if(x==0.0) { 51 INSERT_WORDS(x,uy.bits.sign<<31,1); /* return +-minsubnormal */ 52 t = x*x; 53 if(t==x) return t; else return x; /* raise underflow flag */ 54 } 55 if(hx>0.0 ^ x < y) { /* x -= ulp */ 56 if(lx==0) hx -= 1; 57 lx -= 1; 58 } else { /* x += ulp */ 59 lx += 1; 60 if(lx==0) hx += 1; 61 } 62 ix = hx&0x7ff00000; 63 if(ix>=0x7ff00000) return x+x; /* overflow */ 64 if(ix<0x00100000) { /* underflow */ 65 t = x*x; 66 if(t!=x) { /* raise underflow flag */ 67 INSERT_WORDS(y,hx,lx); 68 return y; 69 } 70 } 71 INSERT_WORDS(x,hx,lx); 72 return x; 73 } 74