doutble2int

lua_number2int.cpp

//http://blog.codingnow.com/2006/02/double_to_int_magic_number.html
//http://www.cnblogs.com/Xiao_bird/archive/2010/03/26/1696908.html  %f--8bytes  %lf--8bytes  %d--4bytes
#include <stdio.h>

union luai_Cast { double l_d; long l_l; };
#define lua_number2int(i,d) { volatile union luai_Cast u; \
	u.l_d = (d) + 6755399441055744.0; (i) = u.l_l; }

int main()
{
	printf("double size: %d;long size:%d; int size:%d\n",sizeof(double),sizeof(long), sizeof(int));
	double d = 1234567890.4;
	int i;
	lua_number2int(i,d);
	printf("input: %f\noutput:%d\n\n",d,i);
	d = 1234567890.5;
	lua_number2int(i,d);
	printf("input: %f\noutput:%d\n\n",d,i);
	d = 1234567890.6;
	lua_number2int(i,d);
	printf("input: %f\noutput:%d\n\n",d,i);
	// d = 2^31-1;
	d = 2147483647.0;
	lua_number2int(i,d);
	printf("input: %f\noutput:%d\n\n",d,i);
	// d = 2^31;
	d = 2147483648.0;
	lua_number2int(i,d);
	printf("input: %f\noutput:%d\n\n",d,i);
	d = 1234567890123.0;
	lua_number2int(i,d);
	printf("input: %f\noutput:%d\n\n",d,i);
	getchar();
	return 0;
}

output：
double size: 8;long size:4; int size:4
input: 1234567890.400000
output:1234567890

input: 1234567890.500000
output:1234567890

input: 1234567890.600000
output:1234567891

input: 2147483647.000000  //此宏只适合处理小于2^31的double，如果大于2^31，则会出错，即之后两个处理都出错了
output:2147483647

input: 2147483648.000000
output:-2147483648

input: 1234567890123.000000
output:1912276171