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 1.6 1994/08/18 23:07:16 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 "math_private.h" 29 30 #ifdef __STDC__ 31 static const double 32 #else 33 static double 34 #endif 35 TWO52[2]={ 36 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */ 37 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */ 38 }; 39 40 #ifdef __STDC__ 41 double rint(double x) 42 #else 43 double rint(x) 44 double x; 45 #endif 46 { 47 int32_t i0,j0,sx; 48 u_int32_t i,i1; 49 double w,t; 50 EXTRACT_WORDS(i0,i1,x); 51 sx = (i0>>31)&1; 52 j0 = ((i0>>20)&0x7ff)-0x3ff; 53 if(j0<20) { 54 if(j0<0) { 55 if(((i0&0x7fffffff)|i1)==0) return x; 56 i1 |= (i0&0x0fffff); 57 i0 &= 0xfffe0000; 58 i0 |= ((i1|-i1)>>12)&0x80000; 59 SET_HIGH_WORD(x,i0); 60 w = TWO52[sx]+x; 61 t = w-TWO52[sx]; 62 GET_HIGH_WORD(i0,t); 63 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31)); 64 return t; 65 } else { 66 i = (0x000fffff)>>j0; 67 if(((i0&i)|i1)==0) return x; /* x is integral */ 68 i>>=1; 69 if(((i0&i)|i1)!=0) { 70 if(j0==19) i1 = 0x40000000; else 71 i0 = (i0&(~i))|((0x20000)>>j0); 72 } 73 } 74 } else if (j0>51) { 75 if(j0==0x400) return x+x; /* inf or NaN */ 76 else return x; /* x is integral */ 77 } else { 78 i = ((u_int32_t)(0xffffffff))>>(j0-20); 79 if((i1&i)==0) return x; /* x is integral */ 80 i>>=1; 81 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20)); 82 } 83 INSERT_WORDS(x,i0,i1); 84 w = TWO52[sx]+x; 85 return w-TWO52[sx]; 86 } 87