简单的itoa函数

参考：~slowe/cpp/itoa.html

// 整型数值转位宽为size的2~16进制字符串，前导0填充对齐。
char* simple_itoa(int value, char* result, int base, int size)
{
	int i;
	int n;
	char* ptr = result;
	char* ptr1 = result;
	char tmp_char;
	int tmp_value;
	//check that the base if valid
	if (base < 2 || base > 16)
	{
		*result = '\0';
		return result;
	}
 
	do {
		tmp_value = value;
		value /= base;
		*ptr++ = "0123456789abcdef"[tmp_value - (value*base)];
	} while (value);
 
	if (tmp_value < 0) *ptr++ = '-'; //Apply negative sign
 
	*ptr = '\0';
	n = strlen(result);
	if (n < size)
	{
		for (i=0; i < (size-n); i++)
		{
			*ptr++ = '0';
		}
		*ptr = '\0';
	}
 
	ptr--;
	while (ptr1 < ptr) {
		tmp_char = *ptr;
		*ptr-- = *ptr1;
		*ptr1++ = tmp_char;
	}
 
	return result;
}