1 2 /* @(#)s_nextafter.c 1.3 95/01/18 */ 3 /* 4 * ==================================================== 5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6 * 7 * Developed at SunSoft, a Sun Microsystems, Inc. business. 8 * Permission to use, copy, modify, and distribute this 9 * software is freely granted, provided that this notice 10 * is preserved. 11 * ==================================================== 12 */ 13 14 /* IEEE functions 15 * nextafter(x,y) 16 * return the next machine floating-point number of x in the 17 * direction toward y. 18 * Special cases: 19 */ 20 21 #include "fdlibm.h" 22 23 #ifdef __STDC__ 24 double ieee_nextafter(double x, double y) 25 #else 26 double ieee_nextafter(x,y) 27 double x,y; 28 #endif 29 { 30 int hx,hy,ix,iy; 31 unsigned lx,ly; 32 33 hx = __HI(x); /* high word of x */ 34 lx = __LO(x); /* low word of x */ 35 hy = __HI(y); /* high word of y */ 36 ly = __LO(y); /* low word of y */ 37 ix = hx&0x7fffffff; /* |x| */ 38 iy = hy&0x7fffffff; /* |y| */ 39 40 if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) || /* x is nan */ 41 ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0)) /* y is nan */ 42 return x+y; 43 if(x==y) return x; /* x=y, return x */ 44 if((ix|lx)==0) { /* x == 0 */ 45 __HI(x) = hy&0x80000000; /* return +-minsubnormal */ 46 __LO(x) = 1; 47 y = x*x; 48 if(y==x) return y; else return x; /* raise underflow flag */ 49 } 50 if(hx>=0) { /* x > 0 */ 51 if(hx>hy||((hx==hy)&&(lx>ly))) { /* x > y, x -= ulp */ 52 if(lx==0) hx -= 1; 53 lx -= 1; 54 } else { /* x < y, x += ulp */ 55 lx += 1; 56 if(lx==0) hx += 1; 57 } 58 } else { /* x < 0 */ 59 if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */ 60 if(lx==0) hx -= 1; 61 lx -= 1; 62 } else { /* x > y, x += ulp */ 63 lx += 1; 64 if(lx==0) hx += 1; 65 } 66 } 67 hy = hx&0x7ff00000; 68 if(hy>=0x7ff00000) return x+x; /* overflow */ 69 if(hy<0x00100000) { /* underflow */ 70 y = x*x; 71 if(y!=x) { /* raise underflow flag */ 72 __HI(y) = hx; __LO(y) = lx; 73 return y; 74 } 75 } 76 __HI(x) = hx; __LO(x) = lx; 77 return x; 78 } 79
