Base64.cpp

#include "Base64.h"
#include <pgmspace.h>
const char PROGMEM 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 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++] = pgm_read_byte(&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++] = pgm_read_byte(&b64_alphabet[a4[j]]);
		}

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

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;
}