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| 2 | /* @(#)s_nextafter.c 5.1 93/09/24 */ |
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| 3 | /* |
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| 4 | * ==================================================== |
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| 5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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| 6 | * |
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| 7 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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| 8 | * Permission to use, copy, modify, and distribute this |
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| 9 | * software is freely granted, provided that this notice |
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| 10 | * is preserved. |
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| 11 | * ==================================================== |
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| 12 | */ |
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| 13 | |
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| 14 | /* IEEE functions |
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| 15 | * nextafter(x,y) |
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| 16 | * return the next machine floating-point number of x in the |
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| 17 | * direction toward y. |
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| 18 | * Special cases: |
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| 19 | */ |
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| 20 | |
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| 21 | #include <libm/fdlibm.h> |
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| 22 | |
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| 23 | #ifdef __STDC__ |
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| 24 | static const double one=1.0; |
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| 25 | #else |
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| 26 | static double one=1.0; |
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| 27 | #endif |
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| 28 | |
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| 29 | #ifdef __STDC__ |
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| 30 | double nextafter(double x, double y) |
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| 31 | #else |
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| 32 | double nextafter(x,y) |
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| 33 | double x,y; |
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| 34 | #endif |
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| 35 | { |
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| 36 | int n0,n1,hx,hy,ix,iy; |
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| 37 | unsigned lx,ly; |
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| 38 | |
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| 39 | n0 = ((*(int*)&one)>>29)^1; /* index of high word */ |
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| 40 | n1 = 1-n0; |
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| 41 | hx = *( n0 + (int*)&x); /* high word of x */ |
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| 42 | lx = *( n1 + (int*)&x); /* low word of x */ |
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| 43 | hy = *( n0 + (int*)&y); /* high word of y */ |
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| 44 | ly = *( n1 + (int*)&y); /* low word of y */ |
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| 45 | ix = hx&0x7fffffff; /* |x| */ |
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| 46 | iy = hy&0x7fffffff; /* |y| */ |
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| 47 | |
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| 48 | if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) || /* x is nan */ |
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| 49 | ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0)) /* y is nan */ |
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| 50 | return x+y; |
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| 51 | if(x==y) return x; /* x=y, return x */ |
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| 52 | if((ix|lx)==0) { /* x == 0 */ |
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| 53 | *(n0+(int*)&x) = hy&0x80000000; /* return +-minsubnormal */ |
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| 54 | *(n1+(int*)&x) = 1; |
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| 55 | y = x*x; |
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| 56 | if(y==x) return y; else return x; /* raise underflow flag */ |
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| 57 | } |
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| 58 | if(hx>=0) { /* x > 0 */ |
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| 59 | if(hx>hy||((hx==hy)&&(lx>ly))) { /* x > y, x -= ulp */ |
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| 60 | if(lx==0) hx -= 1; |
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| 61 | lx -= 1; |
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| 62 | } else { /* x < y, x += ulp */ |
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| 63 | lx += 1; |
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| 64 | if(lx==0) hx += 1; |
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| 65 | } |
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| 66 | } else { /* x < 0 */ |
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| 67 | if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */ |
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| 68 | if(lx==0) hx -= 1; |
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| 69 | lx -= 1; |
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| 70 | } else { /* x > y, x += ulp */ |
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| 71 | lx += 1; |
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| 72 | if(lx==0) hx += 1; |
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| 73 | } |
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| 74 | } |
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| 75 | hy = hx&0x7ff00000; |
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| 76 | if(hy>=0x7ff00000) return x+x; /* overflow */ |
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| 77 | if(hy<0x00100000) { /* underflow */ |
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| 78 | y = x*x; |
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| 79 | if(y!=x) { /* raise underflow flag */ |
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| 80 | *(n0+(int*)&y) = hx; *(n1+(int*)&y) = lx; |
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| 81 | return y; |
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| 82 | } |
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| 83 | } |
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| 84 | *(n0+(int*)&x) = hx; *(n1+(int*)&x) = lx; |
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| 85 | return x; |
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| 86 | } |
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