base64.c

/*********************************************************************
* Filename:   base64.c
* Author:     Brad Conte (brad AT bradconte.com)
* Copyright:
* Disclaimer: This code is presented "as is" without any guarantees.
* Details:    Implementation of the Base64 encoding algorithm.
*********************************************************************/

/*************************** HEADER FILES ***************************/
#include <stdlib.h>
#include "base64.h"

/****************************** MACROS ******************************/
#define NEWLINE_INVL 76

/**************************** VARIABLES *****************************/
// Note: To change the charset to a URL encoding, replace the '+' and '/' with '*' and '-'
static const BYTE charset[]={"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"};

/*********************** FUNCTION DEFINITIONS ***********************/
BYTE revchar(char ch)
{
	if (ch >= 'A' && ch <= 'Z')
		ch -= 'A';
	else if (ch >= 'a' && ch <='z')
		ch = ch - 'a' + 26;
	else if (ch >= '0' && ch <='9')
		ch = ch - '0' + 52;
	else if (ch == '+')
		ch = 62;
	else if (ch == '/')
		ch = 63;

	return(ch);
}

size_t base64_encode(const BYTE in[], BYTE out[], size_t len, int newline_flag)
{
	size_t idx, idx2, blks, blk_ceiling, left_over, newline_count = 0;

	blks = (len / 3);
	left_over = len % 3;

	if (out == NULL) {
		idx2 = blks * 4 ;
		if (left_over)
			idx2 += 4;
		if (newline_flag)
			idx2 += len / 57;   // (NEWLINE_INVL / 4) * 3 = 57. One newline per 57 input bytes.
	}
	else {
		// Since 3 input bytes = 4 output bytes, determine out how many even sets of
		// 3 bytes the input has.
		blk_ceiling = blks * 3;
		for (idx = 0, idx2 = 0; idx < blk_ceiling; idx += 3, idx2 += 4) {
			out[idx2]     = charset[in[idx] >> 2];
			out[idx2 + 1] = charset[((in[idx] & 0x03) << 4) | (in[idx + 1] >> 4)];
			out[idx2 + 2] = charset[((in[idx + 1] & 0x0f) << 2) | (in[idx + 2] >> 6)];
			out[idx2 + 3] = charset[in[idx + 2] & 0x3F];
			// The offical standard requires a newline every 76 characters.
			// (Eg, first newline is character 77 of the output.)
			if (((idx2 - newline_count + 4) % NEWLINE_INVL == 0) && newline_flag) {
				out[idx2 + 4] = '\n';
				idx2++;
				newline_count++;
			}
		}

		if (left_over == 1) {
			out[idx2]     = charset[in[idx] >> 2];
			out[idx2 + 1] = charset[(in[idx] & 0x03) << 4];
			out[idx2 + 2] = '=';
			out[idx2 + 3] = '=';
			idx2 += 4;
		}
		else if (left_over == 2) {
			out[idx2]     = charset[in[idx] >> 2];
			out[idx2 + 1] = charset[((in[idx] & 0x03) << 4) | (in[idx + 1] >> 4)];
			out[idx2 + 2] = charset[(in[idx + 1] & 0x0F) << 2];
			out[idx2 + 3] = '=';
			idx2 += 4;
		}
	}

	return(idx2);
}

size_t base64_decode(const BYTE in[], BYTE out[], size_t len)
{
	BYTE ch;
	size_t idx, idx2, blks, blk_ceiling, left_over;

	if (in[len - 1] == '=')
		len--;
	if (in[len - 1] == '=')
		len--;

	blks = len / 4;
	left_over = len % 4;

	if (out == NULL) {
		if (len >= 77 && in[NEWLINE_INVL] == '\n')   // Verify that newlines where used.
			len -= len / (NEWLINE_INVL + 1);
		blks = len / 4;
		left_over = len % 4;

		idx = blks * 3;
		if (left_over == 2)
			idx ++;
		else if (left_over == 3)
			idx += 2;
	}
	else {
		blk_ceiling = blks * 4;
		for (idx = 0, idx2 = 0; idx2 < blk_ceiling; idx += 3, idx2 += 4) {
			if (in[idx2] == '\n')
				idx2++;
			out[idx]     = (revchar(in[idx2]) << 2) | ((revchar(in[idx2 + 1]) & 0x30) >> 4);
			out[idx + 1] = (revchar(in[idx2 + 1]) << 4) | (revchar(in[idx2 + 2]) >> 2);
			out[idx + 2] = (revchar(in[idx2 + 2]) << 6) | revchar(in[idx2 + 3]);
		}

		if (left_over == 2) {
			out[idx]     = (revchar(in[idx2]) << 2) | ((revchar(in[idx2 + 1]) & 0x30) >> 4);
			idx++;
		}
		else if (left_over == 3) {
			out[idx]     = (revchar(in[idx2]) << 2) | ((revchar(in[idx2 + 1]) & 0x30) >> 4);
			out[idx + 1] = (revchar(in[idx2 + 1]) << 4) | (revchar(in[idx2 + 2]) >> 2);
			idx += 2;
		}
	}

	return(idx);
}