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