math_func.cpp

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00001 /* $Id: math_func.cpp 25347 2013-06-09 12:50:33Z fonsinchen $ */
00002 
00003 /*
00004  * This file is part of OpenTTD.
00005  * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
00006  * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
00007  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
00008  */
00009 
00012 #include "../stdafx.h"
00013 #include "math_func.hpp"
00014 
00024 int LeastCommonMultiple(int a, int b)
00025 {
00026   if (a == 0 || b == 0) return 0; // By definition.
00027   if (a == 1 || a == b) return b;
00028   if (b == 1) return a;
00029 
00030   return a * b / GreatestCommonDivisor(a, b);
00031 }
00032 
00039 int GreatestCommonDivisor(int a, int b)
00040 {
00041   while (b != 0) {
00042     int t = b;
00043     b = a % b;
00044     a = t;
00045   }
00046   return a;
00047 
00048 }
00049 
00057 int DivideApprox(int a, int b)
00058 {
00059   int random_like = ((a + b) * (a - b)) % b;
00060 
00061   int remainder = a % b;
00062 
00063   int ret = a / b;
00064   if (abs(random_like) < abs(remainder)) {
00065     ret += ((a < 0) ^ (b < 0)) ? -1 : 1;
00066   }
00067 
00068   return ret;
00069 }
00070 
00077 uint32 IntSqrt(uint32 num)
00078 {
00079   uint32 res = 0;
00080   uint32 bit = 1UL << 30; // Second to top bit number.
00081 
00082   /* 'bit' starts at the highest power of four <= the argument. */
00083   while (bit > num) bit >>= 2;
00084 
00085   while (bit != 0) {
00086     if (num >= res + bit) {
00087       num -= res + bit;
00088       res = (res >> 1) + bit;
00089     } else {
00090       res >>= 1;
00091     }
00092     bit >>= 2;
00093   }
00094 
00095   /* Arithmetic rounding to nearest integer. */
00096   if (num > res) res++;
00097 
00098   return res;
00099 }