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[] = "$FreeBSD: src/lib/msun/src/s_rint.c,v 1.13 2005/12/03 07:38:35 bde 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 static const double 31 TWO52[2]={ 32 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */ 33 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */ 34 }; 35 36 double 37 rint(double x) 38 { 39 int32_t i0,j0,sx; 40 u_int32_t i,i1; 41 double w,t; 42 EXTRACT_WORDS(i0,i1,x); 43 sx = (i0>>31)&1; 44 j0 = ((i0>>20)&0x7ff)-0x3ff; 45 if(j0<20) { 46 if(j0<0) { 47 if(((i0&0x7fffffff)|i1)==0) return x; 48 i1 |= (i0&0x0fffff); 49 i0 &= 0xfffe0000; 50 i0 |= ((i1|-i1)>>12)&0x80000; 51 SET_HIGH_WORD(x,i0); 52 w = TWO52[sx]+x; 53 t = w-TWO52[sx]; 54 GET_HIGH_WORD(i0,t); 55 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31)); 56 return t; 57 } else { 58 i = (0x000fffff)>>j0; 59 if(((i0&i)|i1)==0) return x; /* x is integral */ 60 i>>=1; 61 if(((i0&i)|i1)!=0) { 62 /* 63 * Some bit is set after the 0.5 bit. To avoid the 64 * possibility of errors from double rounding in 65 * w = TWO52[sx]+x, adjust the 0.25 bit to a lower 66 * guard bit. We do this for all j0<=51. The 67 * adjustment is trickiest for j0==18 and j0==19 68 * since then it spans the word boundary. 69 */ 70 if(j0==19) i1 = 0x40000000; else 71 if(j0==18) i1 = 0x80000000; else 72 i0 = (i0&(~i))|((0x20000)>>j0); 73 } 74 } 75 } else if (j0>51) { 76 if(j0==0x400) return x+x; /* inf or NaN */ 77 else return x; /* x is integral */ 78 } else { 79 i = ((u_int32_t)(0xffffffff))>>(j0-20); 80 if((i1&i)==0) return x; /* x is integral */ 81 i>>=1; 82 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20)); 83 } 84 INSERT_WORDS(x,i0,i1); 85 *(volatile double *)&w = TWO52[sx]+x; /* clip any extra precision */ 86 return w-TWO52[sx]; 87 } 88
