C语言实现的Base64码

C里面可是没有string的，得用char*实现

#include <stdio.h>

#include "Base.h"



const char base[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";



char *base64_encode(const char* data, int data_len)

{

    //int data_len = strlen(data);

    int prepare = 0;

    int ret_len;

    int temp = 0;

    char *ret = NULL;

    char *f = NULL;

    int tmp = 0;

    char changed[4];

    int i = 0;

    ret_len = data_len / 3;

    temp = data_len % 3;

    if (temp > 0)

    {

        ret_len += 1;

    }

    ret_len = ret_len*4 + 1;

    ret = (char *)malloc(ret_len);



    if ( ret == NULL)

    {

        printf("No enough memory.\n");

        exit(0);

    }

    memset(ret, 0, ret_len);

    f = ret;

    while (tmp < data_len)

    {

        temp = 0;

        prepare = 0;

        memset(changed, '\0', 4);

        while (temp < 3)

        {

            //printf("tmp = %d\n", tmp);

            if (tmp >= data_len)

            {

                break;

            }

            prepare = ((prepare << 8) | (data[tmp] & 0xFF));

            tmp++;

            temp++;

        }

        prepare = (prepare<<((3-temp)*8));

        //printf("before for : temp = %d, prepare = %d\n", temp, prepare);

        for (i = 0; i < 4 ;i++ )

        {

            if (temp < i)

            {

                changed[i] = 0x40;

            }

            else

            {

                changed[i] = (prepare>>((3-i)*6)) & 0x3F;

            }

            *f = base[changed[i]];

            //printf("%.2X", changed[i]);

            f++;

        }

    }

    *f = '\0';



    return ret;



}

/*  */

static char find_pos(char ch)

{

    char *ptr = (char*)strrchr(base, ch);//the last position (the only) in base[]

    return (ptr - base);

}

/*  */

char *base64_decode(const char *data, int data_len)

{

    int ret_len = (data_len / 4) * 3;

    int equal_count = 0;

    char *ret = NULL;

    char *f = NULL;

    int tmp = 0;

    int temp = 0;

    char need[3];

    int prepare = 0;

    int i = 0;

    if (*(data + data_len - 1) == '=')

    {

        equal_count += 1;

    }

    if (*(data + data_len - 2) == '=')

    {

        equal_count += 1;

    }

    if (*(data + data_len - 3) == '=')

    {//seems impossible

        equal_count += 1;

    }

    switch (equal_count)

    {

    case 0:

        ret_len += 4;//3 + 1 [1 for NULL]

        break;

    case 1:

        ret_len += 4;//Ceil((6*3)/8)+1

        break;

    case 2:

        ret_len += 3;//Ceil((6*2)/8)+1

        break;

    case 3:

        ret_len += 2;//Ceil((6*1)/8)+1

        break;

    }

    ret = (char *)malloc(ret_len);

    if (ret == NULL)

    {

        printf("No enough memory.\n");

        exit(0);

    }

    memset(ret, 0, ret_len);

    f = ret;

    while (tmp < (data_len - equal_count))

    {

        temp = 0;

        prepare = 0;

        memset(need, 0, 4);

        while (temp < 4)

        {

            if (tmp >= (data_len - equal_count))

            {

                break;

            }

            prepare = (prepare << 6) | (find_pos(data[tmp]));

            temp++;

            tmp++;

        }

        prepare = prepare << ((4-temp) * 6);

        for (i=0; i<3 ;i++ )

        {

            if (i == temp)

            {

                break;

            }

            *f = (char)((prepare>>((2-i)*8)) & 0xFF);

            f++;

        }

    }

    *f = '\0';

    return ret;

}