base64_utils.cpp

#include "base64_utils.h"

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

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

int b64_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 b64_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 b64_enc_len(int plainLen) {
	int n = plainLen;
	return (n + 2 - ((n + 2) % 3)) / 3 * 4;
}

int b64_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) {
	int i;
	for(i = 0; i < 64; i++) {
		if(b64_alphabet[i] == c) {
			return i;
		}
	}

	return -1;
}