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 #include <sys/cdefs.h> 14 __FBSDID("$FreeBSD$"); 15 16 /* 17 * rint(x) 18 * Return x rounded to integral value according to the prevailing 19 * rounding mode. 20 * Method: 21 * Using floating addition. 22 * Exception: 23 * Inexact flag raised if x not equal to rint(x). 24 */ 25 26 #include <float.h> 27 28 #include "math.h" 29 #include "math_private.h" 30 31 static const double 32 TWO52[2]={ 33 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */ 34 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */ 35 }; 36 37 double 38 rint(double x) 39 { 40 int32_t i0,j0,sx; 41 u_int32_t i,i1; 42 double w,t; 43 EXTRACT_WORDS(i0,i1,x); 44 sx = (i0>>31)&1; 45 j0 = ((i0>>20)&0x7ff)-0x3ff; 46 if(j0<20) { 47 if(j0<0) { 48 if(((i0&0x7fffffff)|i1)==0) return x; 49 i1 |= (i0&0x0fffff); 50 i0 &= 0xfffe0000; 51 i0 |= ((i1|-i1)>>12)&0x80000; 52 SET_HIGH_WORD(x,i0); 53 STRICT_ASSIGN(double,w,TWO52[sx]+x); 54 t = w-TWO52[sx]; 55 GET_HIGH_WORD(i0,t); 56 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31)); 57 return t; 58 } else { 59 i = (0x000fffff)>>j0; 60 if(((i0&i)|i1)==0) return x; /* x is integral */ 61 i>>=1; 62 if(((i0&i)|i1)!=0) { 63 /* 64 * Some bit is set after the 0.5 bit. To avoid the 65 * possibility of errors from double rounding in 66 * w = TWO52[sx]+x, adjust the 0.25 bit to a lower 67 * guard bit. We do this for all j0<=51. The 68 * adjustment is trickiest for j0==18 and j0==19 69 * since then it spans the word boundary. 70 */ 71 if(j0==19) i1 = 0x40000000; else 72 if(j0==18) i1 = 0x80000000; else 73 i0 = (i0&(~i))|((0x20000)>>j0); 74 } 75 } 76 } else if (j0>51) { 77 if(j0==0x400) return x+x; /* inf or NaN */ 78 else return x; /* x is integral */ 79 } else { 80 i = ((u_int32_t)(0xffffffff))>>(j0-20); 81 if((i1&i)==0) return x; /* x is integral */ 82 i>>=1; 83 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20)); 84 } 85 INSERT_WORDS(x,i0,i1); 86 STRICT_ASSIGN(double,w,TWO52[sx]+x); 87 return w-TWO52[sx]; 88 } 89 90 #if (LDBL_MANT_DIG == 53) 91 __weak_reference(rint, rintl); 92 #endif 93