// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * base64.c - RFC4648-compliant base64 encoding
 *
 * Copyright (c) 2020 SUSE LLC
 *
 * Author: Hannes Reinecke <hare@suse.de>
 */

#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>

static const char base64_table[65] =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

/**
 * base64_encode() - base64-encode some bytes
 * @src: the bytes to encode
 * @srclen: number of bytes to encode
 * @dst: (output) the base64-encoded string.  Not NUL-terminated.
 *
 * Encodes the input string using characters from the set [A-Za-z0-9+,].
 * The encoded string is roughly 4/3 times the size of the input string.
 *
 * Return: length of the encoded string
 */
int base64_encode(const unsigned char *src, int srclen, char *dst)
{
	int i, bits = 0;
	u_int32_t ac = 0;
	char *cp = dst;

	for (i = 0; i < srclen; i++) {
		ac = (ac << 8) | src[i];
		bits += 8;
		do {
			bits -= 6;
			*cp++ = base64_table[(ac >> bits) & 0x3f];
		} while (bits >= 6);
	}
	if (bits) {
		*cp++ = base64_table[(ac << (6 - bits)) & 0x3f];
		bits -= 6;
	}
	while (bits < 0) {
		*cp++ = '=';
		bits += 2;
	}

	return cp - dst;
}

/**
 * base64_decode() - base64-decode some bytes
 * @src: the base64-encoded string to decode
 * @len: number of bytes to decode
 * @dst: (output) the decoded bytes.
 *
 * Decodes the base64-encoded bytes @src according to RFC 4648.
 *
 * Return: number of decoded bytes
 */
int base64_decode(const char *src, int srclen, unsigned char *dst)
{
	u_int32_t ac = 0;
	int i, bits = 0;
	unsigned char *bp = dst;

	for (i = 0; i < srclen; i++) {
		const char *p = strchr(base64_table, src[i]);

		if (src[i] == '=') {
			ac = (ac << 6);
			bits += 6;
			if (bits >= 8)
				bits -= 8;
			continue;
		}
		if (!p || !src[i])
			return -EINVAL;
		ac = (ac << 6) | (p - base64_table);
		bits += 6;
		if (bits >= 8) {
			bits -= 8;
			*bp++ = (unsigned char)(ac >> bits);
		}
	}
	if (ac && ((1 << bits) - 1))
		return -EAGAIN;

	return bp - dst;
}
