base64.c

包括BASE64编码的C语言实现,DES加密的C实现,共享内存,信号量的C实现

#include "base64.h"

#define BASE64_ENCODE_OP1(ch) base64[(ch >> 2) & 0x3f]
#define	BASE64_ENCODE_OP2(ch1, ch2) base64[((ch1 << 4) & 0x30) | ((ch2 >> 4) & 0x0f)]
#define	BASE64_ENCODE_OP3(ch1, ch2) base64[((ch1 << 2) & 0x3c) | ((ch2 >> 6) & 0x03)]
#define	BASE64_ENCODE_OP4(ch) base64[ch & 0x3f]

#define	BASE64_DECODE_OP1(ch1, ch2) (getbase64pos(ch1) << 2 & 0xfc) | ((getbase64pos(ch2) >> 4) & 0x03) 
#define	BASE64_DECODE_OP2(ch1, ch2) (getbase64pos(ch1) << 4 & 0xf0) | ((getbase64pos(ch2) >> 2) & 0x0f)
#define	BASE64_DECODE_OP3(ch1, ch2) (getbase64pos(ch1) << 6 & 0xc0) | (getbase64pos(ch2) & 0x3f)

char base64[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

int getbase64pos(char ch)
{
	int i;

	for(i=0; i<strlen(base64); i++)
	{
		if (ch == base64[i])
			return i;
	}

	return 0;
}

/* base64 encode, length change 3->4 */
/* "abc"->"61 62 63"->"01100001 01100010 01100011 */
/* 00011000 00010110 00001001 00100011 */
int base64_encode(char *s, int sl, char *d)
{
	int i;
	int rl=0;

	for(i=0; i<sl/3; i++)
	{
		d[i*4] = BASE64_ENCODE_OP1(s[i*3]);
		d[i*4+1] = BASE64_ENCODE_OP2(s[i*3], s[i*3+1]);
		d[i*4+2] = BASE64_ENCODE_OP3(s[i*3+1], s[i*3+2]);
		d[i*4+3] = BASE64_ENCODE_OP4(s[i*3+2]);
	}
	rl = (sl / 3) * 4;
	
	if (sl % 3 == 1)
	{	
		d[i*4] = BASE64_ENCODE_OP1(s[i*3]);
		d[i*4+1] = BASE64_ENCODE_OP2(s[i*3], 0x00);
		d[i*4+2] = '=';
		d[i*4+3] = '=';
		rl += 4;
	}
	else if (sl % 3 == 2)
	{	
		d[i*4] = BASE64_ENCODE_OP1(s[i*3]);
		d[i*4+1] = BASE64_ENCODE_OP2(s[i*3], s[i*3+1]);
		d[i*4+2] = BASE64_ENCODE_OP3(s[i*3+1], 0x00);
		d[i*4+3] = '=';
		rl += 4;
	}
	
	return rl;		
}

/* base64 decode, length change 4->3 */
int base64_decode(char *s, int sl, char *d)
{
	int i;
	
	for(i=0; i<sl/4; i++)
	{
		d[3*i] = BASE64_DECODE_OP1(s[i*4], s[i*4+1]);
		d[3*i+1] = BASE64_DECODE_OP2(s[i*4+1], s[i*4+2]);
		d[3*i+2] = BASE64_DECODE_OP3(s[i*4+2], s[i*4+3]);
	}
	
	return sl * 3 / 4;
}