coreutils

// util/base64.c, version 1.1.5

// Base64 source file from libutil

// Copyright (C) 2021, Jakob Wakeling

// MIT Licence

#include "base64.h"

#include <stdbool.h>

#include <stdint.h>

#include <stdlib.h>

#include <string.h>

static const uint8_t B64E[];

static const uint8_t B64D[];

/* Encode Base64 */

size_t b64encode(uint8_t *dst, uint8_t *src, size_t len) {

	register uint8_t *i = src, *o = dst;

	for (; len >= 3; len -= 3) {

		*o++ = B64E[i[0] >> 2];

		*o++ = B64E[((i[0] & 0x03) << 4) | (i[1] >> 4)];

		*o++ = B64E[((i[1] & 0x0F) << 2) | (i[2] >> 6)];

		*o++ = B64E[i[2] & 0x3F]; i += 3;

	}

	switch (len) {

	case 1: {

		*o++ = B64E[i[0] >> 2];

		*o++ = B64E[(i[0] & 0x03) << 4];

		memset(o, '=', 2); o += 2; break;

	}

	case 2: {

		*o++ = B64E[i[0] >> 2];

		*o++ = B64E[((i[0] & 0x03) << 4) | (i[1] >> 4)];

		*o++ = B64E[(i[1] & 0x0F) << 2];

		*o++ = '='; break;

	}

	}

	return o - dst;

}

/* Decode Base64 */

size_t b64decode(uint8_t *dst, uint8_t *src, size_t len) {

	register uint8_t *i = src, *o = dst;

	for (; src[len - 1] == '='; --len);

	for (; len >= 4; len -= 4) {

		*o++ = (B64D[i[0]] << 2) | (B64D[i[1]] >> 4);

		*o++ = (B64D[i[1]] << 4) | (B64D[i[2]] >> 2);

		*o++ = (B64D[i[2]] << 6) | (B64D[i[3]]); i += 4;

	}

	switch (len) {

	case 2: {

		*o++ = (B64D[i[0]] << 2) | (B64D[i[1]] >> 4);

		*o++ = (B64D[i[1]] << 4); break;

	}

	case 3: {

		*o++ = (B64D[i[0]] << 2) | (B64D[i[1]] >> 4);

		*o++ = (B64D[i[1]] << 4) | (B64D[i[2]] >> 2);

		*o++ = (B64D[i[2]] << 6); break;

	}

	}

	return o - dst;

}

static const uint8_t B64E[] = {

	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',

	'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',

	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',

	'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',

	'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'

};

static const uint8_t B64D[] = {

	 0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,

	 0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,

	 0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 62,  0,  0,  0, 63,

	52, 53, 54, 55, 56, 57, 58, 59, 60, 61,  0,  0,  0,  0,  0,  0,

	 0,  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,  0,  0,  0,  0,  0,

	 0, 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

};