codebackup/bignumber.c at master · M4cr0v/codebackup · GitHub

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/*
 * =====================================================================================
 *
 *       Filename:  bignumber.c
 *
 *    Description:
 *
 *        Version:  1.0
 *        Created:  2012年10月30日 20时48分38秒
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  YOUR NAME (),
 *   Organization:
 *
 * =====================================================================================
 */
#include <stdio.h>
#include <error.h>
#include <errno.h>

//MultiplicationOfBigNumber
void MBN(unsigned char x[], int lengthx, unsigned char y[], int lengthy,
	 unsigned char r[], int lengthr)
{
	int i, j, k, mul;
	if (lengthx + lengthy > lengthr) {
		error_at_line(0, (int) NULL, __FILE__, __LINE__, "%s",
			      "result space is not enough");
	}
	for (i = 0; i < lengthr; i++) {
		r[i] = 0;
	}
	for (i = 0; i < lengthx; i++) {
		for (j = 0; j < lengthy; j++) {
			mul = x[i] * y[j];
			//deal with the carry
			k = i + j;
			while (mul && k < lengthr) {
				mul += r[k];
				r[k] = mul & 0xFF;
				mul = (mul - r[k]) >> 8;
				k++;
			}
		}
	}
}

void MBN_test(void)
{
	unsigned char x[5] = { 0x01, 0x02, 0x03, 0xFF, 0x1F };
	unsigned char y[5] = { 0xAF, 0xFC, 0x2F, 0x00, 0x21 };
	unsigned char r[20] = { 0 };
	int i;
	int lengthx = 5, lengthy = 5, lengthr = 10;
	MBN(x, lengthx, y, lengthy, r, lengthr);
	printf("x = ");
	for (i = lengthx - 1; i >= 0; i--) {
		printf("%02X", x[i]);
	}
	printf("\n");

	printf("y = ");
	for (i = lengthy - 1; i >= 0; i--) {
		printf("%02X", y[i]);
	}
	printf("\n");

	printf("r = x * y = ");
	for (i = lengthr - 1; i >= 0; i--) {
		printf("%02X", r[i]);
	}
	printf("\n");

}