| 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 | SYNOPSIS |
|---|
| 24 | #include <math.h> |
|---|
| 25 | double nextafter(double <[val]>, double <[dir]>); |
|---|
| 26 | float nextafterf(float <[val]>, float <[dir]>); |
|---|
| 27 | |
|---|
| 28 | DESCRIPTION |
|---|
| 29 | <<nextafter>> returns the double-precision floating-point number |
|---|
| 30 | closest to <[val]> in the direction toward <[dir]>. <<nextafterf>> |
|---|
| 31 | performs the same operation in single precision. For example, |
|---|
| 32 | <<nextafter(0.0,1.0)>> returns the smallest positive number which is |
|---|
| 33 | representable in double precision. |
|---|
| 34 | |
|---|
| 35 | RETURNS |
|---|
| 36 | Returns the next closest number to <[val]> in the direction toward |
|---|
| 37 | <[dir]>. |
|---|
| 38 | |
|---|
| 39 | PORTABILITY |
|---|
| 40 | Neither <<nextafter>> nor <<nextafterf>> is required by ANSI C |
|---|
| 41 | or by the System V Interface Definition (Issue 2). |
|---|
| 42 | */ |
|---|
| 43 | |
|---|
| 44 | /* IEEE functions |
|---|
| 45 | * nextafter(x,y) |
|---|
| 46 | * return the next machine floating-point number of x in the |
|---|
| 47 | * direction toward y. |
|---|
| 48 | * Special cases: |
|---|
| 49 | */ |
|---|
| 50 | |
|---|
| 51 | #include "fdlibm.h" |
|---|
| 52 | |
|---|
| 53 | #ifndef _DOUBLE_IS_32BITS |
|---|
| 54 | |
|---|
| 55 | #ifdef __STDC__ |
|---|
| 56 | double nextafter(double x, double y) |
|---|
| 57 | #else |
|---|
| 58 | double nextafter(x,y) |
|---|
| 59 | double x,y; |
|---|
| 60 | #endif |
|---|
| 61 | { |
|---|
| 62 | __int32_t hx,hy,ix,iy; |
|---|
| 63 | __uint32_t lx,ly; |
|---|
| 64 | |
|---|
| 65 | EXTRACT_WORDS(hx,lx,x); |
|---|
| 66 | EXTRACT_WORDS(hy,ly,y); |
|---|
| 67 | ix = hx&0x7fffffff; /* |x| */ |
|---|
| 68 | iy = hy&0x7fffffff; /* |y| */ |
|---|
| 69 | |
|---|
| 70 | if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) || /* x is nan */ |
|---|
| 71 | ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0)) /* y is nan */ |
|---|
| 72 | return x+y; |
|---|
| 73 | if(x==y) return x; /* x=y, return x */ |
|---|
| 74 | if((ix|lx)==0) { /* x == 0 */ |
|---|
| 75 | INSERT_WORDS(x,hy&0x80000000,1); /* return +-minsubnormal */ |
|---|
| 76 | y = x*x; |
|---|
| 77 | if(y==x) return y; else return x; /* raise underflow flag */ |
|---|
| 78 | } |
|---|
| 79 | if(hx>=0) { /* x > 0 */ |
|---|
| 80 | if(hx>hy||((hx==hy)&&(lx>ly))) { /* x > y, x -= ulp */ |
|---|
| 81 | if(lx==0) hx -= 1; |
|---|
| 82 | lx -= 1; |
|---|
| 83 | } else { /* x < y, x += ulp */ |
|---|
| 84 | lx += 1; |
|---|
| 85 | if(lx==0) hx += 1; |
|---|
| 86 | } |
|---|
| 87 | } else { /* x < 0 */ |
|---|
| 88 | if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */ |
|---|
| 89 | if(lx==0) hx -= 1; |
|---|
| 90 | lx -= 1; |
|---|
| 91 | } else { /* x > y, x += ulp */ |
|---|
| 92 | lx += 1; |
|---|
| 93 | if(lx==0) hx += 1; |
|---|
| 94 | } |
|---|
| 95 | } |
|---|
| 96 | hy = hx&0x7ff00000; |
|---|
| 97 | if(hy>=0x7ff00000) return x+x; /* overflow */ |
|---|
| 98 | if(hy<0x00100000) { /* underflow */ |
|---|
| 99 | y = x*x; |
|---|
| 100 | if(y!=x) { /* raise underflow flag */ |
|---|
| 101 | INSERT_WORDS(y,hx,lx); |
|---|
| 102 | return y; |
|---|
| 103 | } |
|---|
| 104 | } |
|---|
| 105 | INSERT_WORDS(x,hx,lx); |
|---|
| 106 | return x; |
|---|
| 107 | } |
|---|
| 108 | |
|---|
| 109 | #endif /* _DOUBLE_IS_32BITS */ |
|---|
