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  #if defined(LIBM_SCCS) && !defined(lint)
14  static char rcsid[] = "$NetBSD: s_nextafter.c,v 1.8 1995/05/10 20:47:58 jtc Exp $";
15  #endif
16  
17  /* IEEE functions
18   *	nextafter(x,y)
19   *	return the next machine floating-point number of x in the
20   *	direction toward y.
21   *   Special cases:
22   */
23  
24  #include "math.h"
25  #include "mathP.h"
26  
27  #ifdef __STDC__
28  	double nextafter(double x, double y)
29  #else
30  	double nextafter(x,y)
31  	double x,y;
32  #endif
33  {
34  	int32_t hx,hy,ix,iy;
35  	u_int32_t lx,ly;
36  
37  	EXTRACT_WORDS(hx,lx,x);
38  	EXTRACT_WORDS(hy,ly,y);
39  	ix = hx&0x7fffffff;		/* |x| */
40  	iy = hy&0x7fffffff;		/* |y| */
41  
42  	if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */ 
43  	   ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */ 
44  	   return x+y;				
45  	if(x==y) return x;		/* x=y, return x */
46  	if((ix|lx)==0) {			/* x == 0 */
47  	    INSERT_WORDS(x,hy&0x80000000,1);	/* return +-minsubnormal */
48  	    y = x*x;
49  	    if(y==x) return y; else return x;	/* raise underflow flag */
50  	} 
51  	if(hx>=0) {				/* x > 0 */
52  	    if(hx>hy||((hx==hy)&&(lx>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(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
61  		if(lx==0) hx -= 1;
62  		lx -= 1;
63  	    } else {				/* x > y, x += ulp */
64  		lx += 1;
65  		if(lx==0) hx += 1;
66  	    }
67  	}
68  	hy = hx&0x7ff00000;
69  	if(hy>=0x7ff00000) return x+x;	/* overflow  */
70  	if(hy<0x00100000) {		/* underflow */
71  	    y = x*x;
72  	    if(y!=x) {		/* raise underflow flag */
73  	        INSERT_WORDS(y,hx,lx);
74  		return y;
75  	    }
76  	}
77  	INSERT_WORDS(x,hx,lx);
78  	return x;
79  }