_modulong.c (1797B)
1/*------------------------------------------------------------------------- 2 _modulong.c - routine for modulus of 32 bit unsigned long 3 4 Copyright (C) 1999, Sandeep Dutta . sandeep.dutta@usa.net 5 Bug fixes by Martijn van Balen, aed@iae.nl 6 7 This library is free software; you can redistribute it and/or modify it 8 under the terms of the GNU General Public License as published by the 9 Free Software Foundation; either version 2, or (at your option) any 10 later version. 11 12 This library is distributed in the hope that it will be useful, 13 but WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 GNU General Public License for more details. 16 17 You should have received a copy of the GNU General Public License 18 along with this library; see the file COPYING. If not, write to the 19 Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston, 20 MA 02110-1301, USA. 21 22 As a special exception, if you link this library with other files, 23 some of which are compiled with SDCC, to produce an executable, 24 this library does not by itself cause the resulting executable to 25 be covered by the GNU General Public License. This exception does 26 not however invalidate any other reasons why the executable file 27 might be covered by the GNU General Public License. 28-------------------------------------------------------------------------*/ 29 30#define MSB_SET(x) ((x >> (8*sizeof(x)-1)) & 1) 31 32unsigned long _modulong (unsigned long a, unsigned long b) 33{ 34 unsigned char count = 0; 35 36 while (!MSB_SET(b)) 37 { 38 b <<= 1; 39 if (b > a) 40 { 41 b >>=1; 42 break; 43 } 44 count++; 45 } 46 do 47 { 48 if (a >= b) 49 a -= b; 50 b >>= 1; 51 } 52 while (count--); 53 54 return a; 55}