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[] = "$FreeBSD$"; 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 <float.h> 28 29 #include "math.h" 30 #include "math_private.h" 31 32 static const double 33 TWO52[2]={ 34 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */ 35 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */ 36 }; 37 38 double 39 rint(double x) 40 { 41 int32_t i0,j0,sx; 42 u_int32_t i,i1; 43 double w,t; 44 EXTRACT_WORDS(i0,i1,x); 45 sx = (i0>>31)&1; 46 j0 = ((i0>>20)&0x7ff)-0x3ff; 47 if(j0<20) { 48 if(j0<0) { 49 if(((i0&0x7fffffff)|i1)==0) return x; 50 i1 |= (i0&0x0fffff); 51 i0 &= 0xfffe0000; 52 i0 |= ((i1|-i1)>>12)&0x80000; 53 SET_HIGH_WORD(x,i0); 54 w = TWO52[sx]+x; 55 t = w-TWO52[sx]; 56 GET_HIGH_WORD(i0,t); 57 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31)); 58 return t; 59 } else { 60 i = (0x000fffff)>>j0; 61 if(((i0&i)|i1)==0) return x; /* x is integral */ 62 i>>=1; 63 if(((i0&i)|i1)!=0) { 64 /* 65 * Some bit is set after the 0.5 bit. To avoid the 66 * possibility of errors from double rounding in 67 * w = TWO52[sx]+x, adjust the 0.25 bit to a lower 68 * guard bit. We do this for all j0<=51. The 69 * adjustment is trickiest for j0==18 and j0==19 70 * since then it spans the word boundary. 71 */ 72 if(j0==19) i1 = 0x40000000; else 73 if(j0==18) i1 = 0x80000000; else 74 i0 = (i0&(~i))|((0x20000)>>j0); 75 } 76 } 77 } else if (j0>51) { 78 if(j0==0x400) return x+x; /* inf or NaN */ 79 else return x; /* x is integral */ 80 } else { 81 i = ((u_int32_t)(0xffffffff))>>(j0-20); 82 if((i1&i)==0) return x; /* x is integral */ 83 i>>=1; 84 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20)); 85 } 86 INSERT_WORDS(x,i0,i1); 87 *(volatile double *)&w = TWO52[sx]+x; /* clip any extra precision */ 88 return w-TWO52[sx]; 89 } 90 91 #if (LDBL_MANT_DIG == 53) 92 __weak_reference(rint, rintl); 93 #endif 94