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 /* IEEE functions
14 * nexttoward(x,y)
15 * return the next machine floating-point number of x in the
16 * direction toward y.
17 * Special cases:
18 */
19
20 #include <math.h>
21 #include <float.h>
22
23 #include "math_private.h"
24
25 double
nexttoward(double x,long double y)26 nexttoward(double x, long double y)
27 {
28 int32_t hx,ix,iy;
29 u_int32_t lx,hy,ly,esy;
30
31 EXTRACT_WORDS(hx,lx,x);
32 GET_LDOUBLE_WORDS(esy,hy,ly,y);
33 ix = hx&0x7fffffff; /* |x| */
34 iy = esy&0x7fff; /* |y| */
35
36 if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) || /* x is nan */
37 ((iy>=0x7fff)&&(hy|ly)!=0)) /* y is nan */
38 return x+y;
39 if((long double) x==y) return y; /* x=y, return y */
40 if((ix|lx)==0) { /* x == 0 */
41 volatile double u;
42 INSERT_WORDS(x,(esy&0x8000)<<16,1); /* return +-minsub */
43 u = x;
44 u = u * u; /* raise underflow flag */
45 return x;
46 }
47 if(hx>=0) { /* x > 0 */
48 if (esy>=0x8000||((ix>>20)&0x7ff)>iy-0x3c00
49 || (((ix>>20)&0x7ff)==iy-0x3c00
50 && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
51 || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
52 && (lx<<11)>ly)))) { /* x > y, x -= ulp */
53 if(lx==0) hx -= 1;
54 lx -= 1;
55 } else { /* x < y, x += ulp */
56 lx += 1;
57 if(lx==0) hx += 1;
58 }
59 } else { /* x < 0 */
60 if (esy<0x8000||((ix>>20)&0x7ff)>iy-0x3c00
61 || (((ix>>20)&0x7ff)==iy-0x3c00
62 && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
63 || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
64 && (lx<<11)>ly)))) {/* x < y, x -= ulp */
65 if(lx==0) hx -= 1;
66 lx -= 1;
67 } else { /* x > y, x += ulp */
68 lx += 1;
69 if(lx==0) hx += 1;
70 }
71 }
72 hy = hx&0x7ff00000;
73 if(hy>=0x7ff00000) {
74 x = x+x; /* overflow */
75 return x;
76 }
77 if(hy<0x00100000) {
78 volatile double u = x*x; /* underflow */
79 if(u==x) {
80 INSERT_WORDS(x,hx,lx);
81 return x;
82 }
83 }
84 INSERT_WORDS(x,hx,lx);
85 return x;
86 }
87