1*05a0b428SJohn Marino /* @(#)s_nextafter.c 5.1 93/09/24 */
2*05a0b428SJohn Marino /*
3*05a0b428SJohn Marino * ====================================================
4*05a0b428SJohn Marino * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5*05a0b428SJohn Marino *
6*05a0b428SJohn Marino * Developed at SunPro, a Sun Microsystems, Inc. business.
7*05a0b428SJohn Marino * Permission to use, copy, modify, and distribute this
8*05a0b428SJohn Marino * software is freely granted, provided that this notice
9*05a0b428SJohn Marino * is preserved.
10*05a0b428SJohn Marino * ====================================================
11*05a0b428SJohn Marino */
12*05a0b428SJohn Marino
13*05a0b428SJohn Marino /* IEEE functions
14*05a0b428SJohn Marino * nexttoward(x,y)
15*05a0b428SJohn Marino * return the next machine floating-point number of x in the
16*05a0b428SJohn Marino * direction toward y.
17*05a0b428SJohn Marino * Special cases:
18*05a0b428SJohn Marino */
19*05a0b428SJohn Marino
20*05a0b428SJohn Marino #include <math.h>
21*05a0b428SJohn Marino #include <float.h>
22*05a0b428SJohn Marino
23*05a0b428SJohn Marino #include "math_private.h"
24*05a0b428SJohn Marino
25*05a0b428SJohn Marino double
nexttoward(double x,long double y)26*05a0b428SJohn Marino nexttoward(double x, long double y)
27*05a0b428SJohn Marino {
28*05a0b428SJohn Marino int32_t hx,ix,iy;
29*05a0b428SJohn Marino u_int32_t lx,hy,ly,esy;
30*05a0b428SJohn Marino
31*05a0b428SJohn Marino EXTRACT_WORDS(hx,lx,x);
32*05a0b428SJohn Marino GET_LDOUBLE_WORDS(esy,hy,ly,y);
33*05a0b428SJohn Marino ix = hx&0x7fffffff; /* |x| */
34*05a0b428SJohn Marino iy = esy&0x7fff; /* |y| */
35*05a0b428SJohn Marino
36*05a0b428SJohn Marino if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) || /* x is nan */
37*05a0b428SJohn Marino ((iy>=0x7fff)&&(hy|ly)!=0)) /* y is nan */
38*05a0b428SJohn Marino return x+y;
39*05a0b428SJohn Marino if((long double) x==y) return y; /* x=y, return y */
40*05a0b428SJohn Marino if((ix|lx)==0) { /* x == 0 */
41*05a0b428SJohn Marino volatile double u;
42*05a0b428SJohn Marino INSERT_WORDS(x,(esy&0x8000)<<16,1); /* return +-minsub */
43*05a0b428SJohn Marino u = x;
44*05a0b428SJohn Marino u = u * u; /* raise underflow flag */
45*05a0b428SJohn Marino return x;
46*05a0b428SJohn Marino }
47*05a0b428SJohn Marino if(hx>=0) { /* x > 0 */
48*05a0b428SJohn Marino if (esy>=0x8000||((ix>>20)&0x7ff)>iy-0x3c00
49*05a0b428SJohn Marino || (((ix>>20)&0x7ff)==iy-0x3c00
50*05a0b428SJohn Marino && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
51*05a0b428SJohn Marino || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
52*05a0b428SJohn Marino && (lx<<11)>ly)))) { /* x > y, x -= ulp */
53*05a0b428SJohn Marino if(lx==0) hx -= 1;
54*05a0b428SJohn Marino lx -= 1;
55*05a0b428SJohn Marino } else { /* x < y, x += ulp */
56*05a0b428SJohn Marino lx += 1;
57*05a0b428SJohn Marino if(lx==0) hx += 1;
58*05a0b428SJohn Marino }
59*05a0b428SJohn Marino } else { /* x < 0 */
60*05a0b428SJohn Marino if (esy<0x8000||((ix>>20)&0x7ff)>iy-0x3c00
61*05a0b428SJohn Marino || (((ix>>20)&0x7ff)==iy-0x3c00
62*05a0b428SJohn Marino && (((hx<<11)|(lx>>21))>(hy&0x7fffffff)
63*05a0b428SJohn Marino || (((hx<<11)|(lx>>21))==(hy&0x7fffffff)
64*05a0b428SJohn Marino && (lx<<11)>ly)))) {/* x < y, x -= ulp */
65*05a0b428SJohn Marino if(lx==0) hx -= 1;
66*05a0b428SJohn Marino lx -= 1;
67*05a0b428SJohn Marino } else { /* x > y, x += ulp */
68*05a0b428SJohn Marino lx += 1;
69*05a0b428SJohn Marino if(lx==0) hx += 1;
70*05a0b428SJohn Marino }
71*05a0b428SJohn Marino }
72*05a0b428SJohn Marino hy = hx&0x7ff00000;
73*05a0b428SJohn Marino if(hy>=0x7ff00000) {
74*05a0b428SJohn Marino x = x+x; /* overflow */
75*05a0b428SJohn Marino return x;
76*05a0b428SJohn Marino }
77*05a0b428SJohn Marino if(hy<0x00100000) {
78*05a0b428SJohn Marino volatile double u = x*x; /* underflow */
79*05a0b428SJohn Marino if(u==x) {
80*05a0b428SJohn Marino INSERT_WORDS(x,hx,lx);
81*05a0b428SJohn Marino return x;
82*05a0b428SJohn Marino }
83*05a0b428SJohn Marino }
84*05a0b428SJohn Marino INSERT_WORDS(x,hx,lx);
85*05a0b428SJohn Marino return x;
86*05a0b428SJohn Marino }
87