base64编码.c

BASE64编码的实现

#include <stdio.h>
#include <conio.h>
#include <mem.h>
#include <malloc.h>

char* EncodeBase64(const char* pVal ,int len)
{
    static const char*index= "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    const char* p = pVal;
    //char*const pRet = new char[len*4/3+16];
    char*const pRet = (char*)malloc(len*4/3+16);
    memset( pRet , 0 , len*4/3+16 );
    char* pOut=pRet;
    while( len >=3 ){
        pOut[0] = index[(p[0]>>2)&0x3f];
        pOut[1] = index[(((p[0]<<6)>>2)| (p[1]>>4))&0x3f];
        pOut[2] = index[((p[1]<<4>>2) | (p[2]>>6))&0x3f];
        pOut[3] = index[(p[2]<<2>>2)&0x3f];
        len-=3;
        p+=3;
        pOut+=4;
        pOut[0]=0;
    }
    if( 2==len){
        pOut[0] = index[(p[0]>>2)&0x3f];
        pOut[1] = index[(((p[0]<<6)>>2)| (p[1]>>4))&0x3f];
        pOut[2] = index[(p[1]<<4>>2)&0x3f];
        pOut[3] = '=';
        pOut[4]=0;
    }else if( 1==len){
        pOut[0] = index[(p[0]>>2)&0x3f];
        pOut[1] = index[((p[0]<<6)>>2)&0x3f];
        pOut[2] = '=';
        pOut[3] = '=';
        pOut[4]=0;
    }
    return pRet;
}
int DecodeBase64(const char* p,char* pOut)
{
    int len =0;
    size_t i;
    static const char index[]={62,0,0,0,63,52,53,54,55,56,57,58,59,60,61,
        0,0,0,64,0,0,0,0,1,2,3,4,5,6,7,8,9,
        10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,
        0,0,0,0,0,0,26,27,28,29,30,31,32,33,
        34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
    size_t l = strlen( p );
    for(i=0; i<l-4;i+=4){
        pOut[0] = index[ p[0]-0x2b ]<<2|index[ p[1]-0x2b ]<<2>>6;
        pOut[1] = index[ p[1]-0x2b ]<<4|index[ p[2]-0x2b ]<<2>>4;
        pOut[2] = index[ p[2]-0x2b ]<<6|index[ p[3]-0x2b ]<<2>>2;
        pOut+=3;
        len+=3;
        p+=4;
    }
    if( '=' == p[2] ){
        pOut[0] = index[ p[0]-0x2b ]<<2|index[ p[1]-0x2b ]<<2>>6;
        pOut[1]=0;
        len++;
    }else if( '=' == p[3] ){
        pOut[0] = index[ p[0]-0x2b ]<<2|index[ p[1]-0x2b ]<<2>>6;
        pOut[1] = index[ p[1]-0x2b ]<<4|index[ p[2]-0x2b ]<<2>>4;
        pOut[2]=0;
        len+=2;
    }else{
        pOut[0] = index[ p[0]-0x2b ]<<2|index[ p[1]-0x2b ]<<2>>6;
        pOut[1] = index[ p[1]-0x2b ]<<4|index[ p[2]-0x2b ]<<2>>4;
        pOut[2] = index[ p[2]-0x2b ]<<6|index[ p[3]-0x2b ]<<2>>2;
        pOut[3]=0;
        len+=3;
    }
    return len;
}
int main()
{
    char* src = "1234ABCD";
    char* p = (char*)malloc(strlen(src)*2);
    char* decodeB = (char*)malloc(strlen(src));
    p = EncodeBase64(src,strlen(src));
    printf("%s\n",p);
    DecodeBase64(p,decodeB);
    printf("%s\n",decodeB);
    getch();
    return 0;
}