1 /*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12 /*
13 * We assume that a long double has a 15-bit exponent. On systems
14 * where long double is the same as double, nexttoward() is an alias
15 * for nextafter(), so we don't use this routine.
16 */
17
18 #include <float.h>
19
20 #include "fpmath.h"
21 #include "math.h"
22 #include "math_private.h"
23
24 #if LDBL_MAX_EXP != 0x4000
25 #error "Unsupported long double format"
26 #endif
27
28 double
nexttoward(double x,long double y)29 nexttoward(double x, long double y)
30 {
31 union IEEEl2bits uy;
32 volatile double t;
33 int32_t hx,ix;
34 u_int32_t lx;
35
36 EXTRACT_WORDS(hx,lx,x);
37 ix = hx&0x7fffffff; /* |x| */
38 uy.e = y;
39
40 if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||
41 (uy.bits.exp == 0x7fff &&
42 ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl) != 0))
43 return x+y; /* x or y is nan */
44 if(x==y) return (double)y; /* x=y, return y */
45 if(x==0.0) {
46 INSERT_WORDS(x,uy.bits.sign<<31,1); /* return +-minsubnormal */
47 t = x*x;
48 if(t==x) return t; else return x; /* raise underflow flag */
49 }
50 if(hx>0.0 ^ x < y) { /* x -= ulp */
51 if(lx==0) hx -= 1;
52 lx -= 1;
53 } else { /* x += ulp */
54 lx += 1;
55 if(lx==0) hx += 1;
56 }
57 ix = hx&0x7ff00000;
58 if(ix>=0x7ff00000) return x+x; /* overflow */
59 if(ix<0x00100000) { /* underflow */
60 t = x*x;
61 if(t!=x) { /* raise underflow flag */
62 INSERT_WORDS(x,hx,lx);
63 return x;
64 }
65 }
66 INSERT_WORDS(x,hx,lx);
67 return x;
68 }
69