1 /* @(#)s_rint.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 #ifndef lint 14 static char rcsid[] = "$Id: s_rint.c,v 1.4 1994/03/03 17:04:45 jtc Exp $"; 15 #endif 16 17 /* 18 * rint(x) 19 * Return x rounded to integral value according to the prevailing 20 * rounding mode. 21 * Method: 22 * Using floating addition. 23 * Exception: 24 * Inexact flag raised if x not equal to rint(x). 25 */ 26 27 #include <math.h> 28 #include <machine/endian.h> 29 30 #if BYTE_ORDER == LITTLE_ENDIAN 31 #define n0 1 32 #else 33 #define n0 0 34 #endif 35 36 #ifdef __STDC__ 37 static const double 38 #else 39 static double 40 #endif 41 TWO52[2]={ 42 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */ 43 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */ 44 }; 45 46 #ifdef __STDC__ 47 double rint(double x) 48 #else 49 double rint(x) 50 double x; 51 #endif 52 { 53 int i0,j0,sx; 54 unsigned i,i1; 55 double w,t; 56 i0 = *(n0+(int*)&x); 57 sx = (i0>>31)&1; 58 i1 = *(1-n0+(int*)&x); 59 j0 = ((i0>>20)&0x7ff)-0x3ff; 60 if(j0<20) { 61 if(j0<0) { 62 if(((i0&0x7fffffff)|i1)==0) return x; 63 i1 |= (i0&0x0fffff); 64 i0 &= 0xfffe0000; 65 i0 |= ((i1|-i1)>>12)&0x80000; 66 *(n0+(int*)&x)=i0; 67 w = TWO52[sx]+x; 68 t = w-TWO52[sx]; 69 i0 = *(n0+(int*)&t); 70 *(n0+(int*)&t) = (i0&0x7fffffff)|(sx<<31); 71 return t; 72 } else { 73 i = (0x000fffff)>>j0; 74 if(((i0&i)|i1)==0) return x; /* x is integral */ 75 i>>=1; 76 if(((i0&i)|i1)!=0) { 77 if(j0==19) i1 = 0x40000000; else 78 i0 = (i0&(~i))|((0x20000)>>j0); 79 } 80 } 81 } else if (j0>51) { 82 if(j0==0x400) return x+x; /* inf or NaN */ 83 else return x; /* x is integral */ 84 } else { 85 i = ((unsigned)(0xffffffff))>>(j0-20); 86 if((i1&i)==0) return x; /* x is integral */ 87 i>>=1; 88 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20)); 89 } 90 *(n0+(int*)&x) = i0; 91 *(1-n0+(int*)&x) = i1; 92 w = TWO52[sx]+x; 93 return w-TWO52[sx]; 94 } 95