base64.c

#include <inttypes.h>
#include <string.h>

int base64encode(const void* data_buf, size_t dataLength, char* result, size_t resultSize)
{
	const char base64chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
	const uint8_t *data = (const uint8_t *)data_buf;
	size_t resultIndex = 0;
	size_t x;
	uint32_t n = 0;
	int padCount = dataLength % 3;
	uint8_t n0, n1, n2, n3;

	/* increment over the length of the string, three characters at a time */
	for (x = 0; x < dataLength; x += 3)
	{
		/* these three 8-bit (ASCII) characters become one 24-bit number */
		n = ((uint32_t)data[x]) << 16; //parenthesis needed, compiler depending on flags can do the shifting before conversion to uint32_t, resulting to 0

		if ((x + 1) < dataLength)
			n += ((uint32_t)data[x + 1]) << 8;//parenthesis needed, compiler depending on flags can do the shifting before conversion to uint32_t, resulting to 0

		if ((x + 2) < dataLength)
			n += data[x + 2];

		/* this 24-bit number gets separated into four 6-bit numbers */
		n0 = (uint8_t)(n >> 18) & 63;
		n1 = (uint8_t)(n >> 12) & 63;
		n2 = (uint8_t)(n >> 6) & 63;
		n3 = (uint8_t)n & 63;

		/*
		* if we have one byte available, then its encoding is spread
		* out over two characters
		*/
		if (resultIndex >= resultSize) return 1;   /* indicate failure: buffer too small */
		result[resultIndex++] = base64chars[n0];
		if (resultIndex >= resultSize) return 1;   /* indicate failure: buffer too small */
		result[resultIndex++] = base64chars[n1];

		/*
		* if we have only two bytes available, then their encoding is
		* spread out over three chars
		*/
		if ((x + 1) < dataLength)
		{
			if (resultIndex >= resultSize) return 1;   /* indicate failure: buffer too small */
			result[resultIndex++] = base64chars[n2];
		}

		/*
		* if we have all three bytes available, then their encoding is spread
		* out over four characters
		*/
		if ((x + 2) < dataLength)
		{
			if (resultIndex >= resultSize) return 1;   /* indicate failure: buffer too small */
			result[resultIndex++] = base64chars[n3];
		}
	}

	/*
	* create and add padding that is required if we did not have a multiple of 3
	* number of characters available
	*/
	if (padCount > 0)
	{
		for (; padCount < 3; padCount++)
		{
			if (resultIndex >= resultSize) return 1;   /* indicate failure: buffer too small */
			result[resultIndex++] = '=';
		}
	}
	if (resultIndex >= resultSize) return 1;   /* indicate failure: buffer too small */
	result[resultIndex] = 0;
	return 0;   /* indicate success */
}

#define WHITESPACE 64
#define EQUALS     65
#define INVALID    66

static const unsigned char d[] = {
	66,66,66,66,66,66,66,66,66,66,64,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
	66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,62,66,66,66,63,52,53,
	54,55,56,57,58,59,60,61,66,66,66,65,66,66,66, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
	10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,66,66,66,66,66,66,26,27,28,
	29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,66,66,
	66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
	66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
	66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
	66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
	66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,66,
	66,66,66,66,66,66
};

int base64decode(char *in, size_t inLen, unsigned char *out, size_t *outLen)
{
	char *end = in + inLen;
	char iter = 0;
	uint32_t buf = 0;
	size_t len = 0;

	while (in < end) {
		unsigned char c = d[*in++];

		switch (c) {
		case WHITESPACE: continue;   /* skip whitespace */
		case INVALID:    return 1;   /* invalid input, return error */
		case EQUALS:                 /* pad character, end of data */
			in = end;
			continue;
		default:
			buf = buf << 6 | c;
			iter++; // increment the number of iteration
					/* If the buffer is full, split it into bytes */
			if (iter == 4) {
				if ((len += 3) > *outLen) return 1; /* buffer overflow */
				*(out++) = (buf >> 16) & 255;
				*(out++) = (buf >> 8) & 255;
				*(out++) = buf & 255;
				buf = 0; iter = 0;

			}
		}
	}

	if (iter == 3) {
		if ((len += 2) > *outLen) return 1; /* buffer overflow */
		*(out++) = (buf >> 10) & 255;
		*(out++) = (buf >> 2) & 255;
	}
	else if (iter == 2) {
		if (++len > *outLen) return 1; /* buffer overflow */
		*(out++) = (buf >> 4) & 255;
	}

	*outLen = len; /* modify to reflect the actual output size */
	return 0;
}