1 
2 /* @(#)s_nextafter.c 5.1 93/09/24 */
3 /*
4  * ====================================================
5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6  *
7  * Developed at SunPro, 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 /*
15 FUNCTION
16        <<nextafter>>, <<nextafterf>>---get next number
17 
18 INDEX
19 	nextafter
20 INDEX
21 	nextafterf
22 
23 ANSI_SYNOPSIS
24        #include <math.h>
25        double nextafter(double <[val]>, double <[dir]>);
26        float nextafterf(float <[val]>, float <[dir]>);
27 
28 TRAD_SYNOPSIS
29        #include <math.h>
30 
31        double nextafter(<[val]>, <[dir]>)
32               double <[val]>;
33               double <[exp]>;
34 
35        float nextafter(<[val]>, <[dir]>)
36               float <[val]>;
37               float <[dir]>;
38 
39 
40 DESCRIPTION
41 <<nextafter>> returns the double-precision floating-point number
42 closest to <[val]> in the direction toward <[dir]>.  <<nextafterf>>
43 performs the same operation in single precision.  For example,
44 <<nextafter(0.0,1.0)>> returns the smallest positive number which is
45 representable in double precision.
46 
47 RETURNS
48 Returns the next closest number to <[val]> in the direction toward
49 <[dir]>.
50 
51 PORTABILITY
52 	Neither <<nextafter>> nor <<nextafterf>> is required by ANSI C
53 	or by the System V Interface Definition (Issue 2).
54 */
55 
56 /* IEEE functions
57  *	nextafter(x,y)
58  *	return the next machine floating-point number of x in the
59  *	direction toward y.
60  *   Special cases:
61  */
62 
63 #include "fdlibm.h"
64 
65 #ifndef _DOUBLE_IS_32BITS
66 
67 #ifdef __STDC__
nextafter(double x,double y)68 	double nextafter(double x, double y)
69 #else
70 	double nextafter(x,y)
71 	double x,y;
72 #endif
73 {
74 	__int32_t	hx,hy,ix,iy;
75 	__uint32_t lx,ly;
76 
77 	EXTRACT_WORDS(hx,lx,x);
78 	EXTRACT_WORDS(hy,ly,y);
79 	ix = hx&0x7fffffff;		/* |x| */
80 	iy = hy&0x7fffffff;		/* |y| */
81 
82 	if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
83 	   ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
84 	   return x+y;
85 	if(x==y) return x;		/* x=y, return x */
86 	if((ix|lx)==0) {			/* x == 0 */
87 	    INSERT_WORDS(x,hy&0x80000000,1);	/* return +-minsubnormal */
88 	    y = x*x;
89 	    if(y==x) return y; else return x;	/* raise underflow flag */
90 	}
91 	if(hx>=0) {				/* x > 0 */
92 	    if(hx>hy||((hx==hy)&&(lx>ly))) {	/* x > y, x -= ulp */
93 		if(lx==0) hx -= 1;
94 		lx -= 1;
95 	    } else {				/* x < y, x += ulp */
96 		lx += 1;
97 		if(lx==0) hx += 1;
98 	    }
99 	} else {				/* x < 0 */
100 	    if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
101 		if(lx==0) hx -= 1;
102 		lx -= 1;
103 	    } else {				/* x > y, x += ulp */
104 		lx += 1;
105 		if(lx==0) hx += 1;
106 	    }
107 	}
108 	hy = hx&0x7ff00000;
109 	if(hy>=0x7ff00000) return x+x;	/* overflow  */
110 	if(hy<0x00100000) {		/* underflow */
111 	    y = x*x;
112 	    if(y!=x) {		/* raise underflow flag */
113 	        INSERT_WORDS(y,hx,lx);
114 		return y;
115 	    }
116 	}
117 	INSERT_WORDS(x,hx,lx);
118 	return x;
119 }
120 
121 #endif /* _DOUBLE_IS_32BITS */
122