| The Android Open Source Project | 1dc9e47 | 2009-03-03 19:28:35 -0800 | [diff] [blame] | 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 | } |