base64.c

#include "base64.h"

const char b64_alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/";

/* 'Private' declarations */
void a3_to_a4(unsigned char * a4, unsigned char * a3);
void a4_to_a3(unsigned char * a3, unsigned char * a4);
unsigned char b64_lookup(char c);

int base64_encode(char *output, char *input, int inputLen) {
        int i = 0, j = 0;
        int encLen = 0;
        unsigned char a3[3];
        unsigned char a4[4];

        while(inputLen--) {
                a3[i++] = *(input++);
                if(i == 3) {
                        a3_to_a4(a4, a3);

                        for(i = 0; i < 4; i++) {
                                output[encLen++] = b64_alphabet[a4[i]];
                        }

                        i = 0;
                }
        }

        if(i) {
                for(j = i; j < 3; j++) {
                        a3[j] = '\0';
                }

                a3_to_a4(a4, a3);

                for(j = 0; j < i + 1; j++) {
                        output[encLen++] = b64_alphabet[a4[j]];
                }

                while((i++ < 3)) {
                        output[encLen++] = '=';
                }
        }
        output[encLen] = '\0';
        return encLen;
}

int base64_decode(char * output, char * input, int inputLen) {
        int i = 0, j = 0;
        int decLen = 0;
        unsigned char a3[3];
        unsigned char a4[4];


        while (inputLen--) {
                if(*input == '=') {
                        break;
                }

                a4[i++] = *(input++);
                if (i == 4) {
                        for (i = 0; i <4; i++) {
                                a4[i] = b64_lookup(a4[i]);
                        }

                        a4_to_a3(a3,a4);

                        for (i = 0; i < 3; i++) {
                                output[decLen++] = a3[i];
                        }
                        i = 0;
                }
        }

        if (i) {
                for (j = i; j < 4; j++) {
                        a4[j] = '\0';
                }

                for (j = 0; j <4; j++) {
                        a4[j] = b64_lookup(a4[j]);
                }

                a4_to_a3(a3,a4);

                for (j = 0; j < i - 1; j++) {
                        output[decLen++] = a3[j];
                }
        }
        output[decLen] = '\0';
        return decLen;
}

int base64_dec_len(char * input, int inputLen) {
        int i = 0;
        int numEq = 0;
        for(i = inputLen - 1; input[i] == '='; i--) {
                numEq++;
        }

        return ((6 * inputLen) / 8) - numEq;
}

inline void a3_to_a4(unsigned char * a4, unsigned char * a3) {
        a4[0] = (a3[0] & 0xfc) >> 2;
        a4[1] = ((a3[0] & 0x03) << 4) + ((a3[1] & 0xf0) >> 4);
        a4[2] = ((a3[1] & 0x0f) << 2) + ((a3[2] & 0xc0) >> 6);
        a4[3] = (a3[2] & 0x3f);
}

inline void a4_to_a3(unsigned char * a3, unsigned char * a4) {
        a3[0] = (a4[0] << 2) + ((a4[1] & 0x30) >> 4);
        a3[1] = ((a4[1] & 0xf) << 4) + ((a4[2] & 0x3c) >> 2);
        a3[2] = ((a4[2] & 0x3) << 6) + a4[3];
}

inline unsigned char b64_lookup(char c) {
        if(c >='A' && c <='Z') return c - 'A';
        if(c >='a' && c <='z') return c - 71;
        if(c >='0' && c <='9') return c + 4;
        if(c == '+') return 62;
        if(c == '/') return 63;
        return -1;
}