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const assert = @import("debug.zig").assert;
const mem = @import("mem.zig");
pub const standard_alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
pub fn encode(dest: []u8, source: []const u8) -> []u8 {
return encodeWithAlphabet(dest, source, standard_alphabet);
}
pub fn decode(dest: []u8, source: []const u8) -> []u8 {
return decodeWithAlphabet(dest, source, standard_alphabet);
}
pub fn encodeWithAlphabet(dest: []u8, source: []const u8, alphabet: []const u8) -> []u8 {
assert(alphabet.len == 65);
assert(dest.len >= calcEncodedSize(source.len));
var i: usize = 0;
var out_index: usize = 0;
while (i + 2 < source.len; i += 3) {
dest[out_index] = alphabet[(source[i] >> 2) & 0x3f];
out_index += 1;
dest[out_index] = alphabet[((source[i] & 0x3) <<% 4) |
((source[i + 1] & 0xf0) >> 4)];
out_index += 1;
dest[out_index] = alphabet[((source[i + 1] & 0xf) <<% 2) |
((source[i + 2] & 0xc0) >> 6)];
out_index += 1;
dest[out_index] = alphabet[source[i + 2] & 0x3f];
out_index += 1;
}
if (i < source.len) {
dest[out_index] = alphabet[(source[i] >> 2) & 0x3f];
out_index += 1;
if (i + 1 == source.len) {
dest[out_index] = alphabet[(source[i] & 0x3) <<% 4];
out_index += 1;
dest[out_index] = alphabet[64];
out_index += 1;
} else {
dest[out_index] = alphabet[((source[i] & 0x3) <<% 4) |
((source[i + 1] & 0xf0) >> 4)];
out_index += 1;
dest[out_index] = alphabet[(source[i + 1] & 0xf) <<% 2];
out_index += 1;
}
dest[out_index] = alphabet[64];
out_index += 1;
}
return dest[0...out_index];
}
pub fn decodeWithAlphabet(dest: []u8, source: []const u8, alphabet: []const u8) -> []u8 {
assert(alphabet.len == 65);
var ascii6 = []u8{64} ** 256;
for (alphabet) |c, i| {
ascii6[c] = u8(i);
}
return decodeWithAscii6BitMap(dest, source, ascii6[0...], alphabet[64]);
}
pub fn decodeWithAscii6BitMap(dest: []u8, source: []const u8, ascii6: []const u8, pad_char: u8) -> []u8 {
assert(ascii6.len == 256);
assert(dest.len >= calcExactDecodedSizeWithPadChar(source, pad_char));
var src_index: usize = 0;
var dest_index: usize = 0;
var in_buf_len: usize = source.len;
while (in_buf_len > 0 and source[in_buf_len - 1] == pad_char) {
in_buf_len -= 1;
}
while (in_buf_len > 4) {
dest[dest_index] = ascii6[source[src_index + 0]] <<% 2 |
ascii6[source[src_index + 1]] >> 4;
dest_index += 1;
dest[dest_index] = ascii6[source[src_index + 1]] <<% 4 |
ascii6[source[src_index + 2]] >> 2;
dest_index += 1;
dest[dest_index] = ascii6[source[src_index + 2]] <<% 6 |
ascii6[source[src_index + 3]];
dest_index += 1;
src_index += 4;
in_buf_len -= 4;
}
if (in_buf_len > 1) {
dest[dest_index] = ascii6[source[src_index + 0]] <<% 2 |
ascii6[source[src_index + 1]] >> 4;
dest_index += 1;
}
if (in_buf_len > 2) {
dest[dest_index] = ascii6[source[src_index + 1]] <<% 4 |
ascii6[source[src_index + 2]] >> 2;
dest_index += 1;
}
if (in_buf_len > 3) {
dest[dest_index] = ascii6[source[src_index + 2]] <<% 6 |
ascii6[source[src_index + 3]];
dest_index += 1;
}
return dest[0...dest_index];
}
pub fn calcEncodedSize(source_len: usize) -> usize {
return (((source_len * 4) / 3 + 3) / 4) * 4;
}
/// Computes the upper bound of the decoded size based only on the encoded length.
/// To compute the exact decoded size, see ::calcExactDecodedSize
pub fn calcMaxDecodedSize(encoded_len: usize) -> usize {
return @divExact(encoded_len * 3, 4);
}
/// Computes the number of decoded bytes there will be. This function must
/// be given the encoded buffer because there might be padding
/// bytes at the end ('=' in the standard alphabet)
pub fn calcExactDecodedSize(encoded: []const u8) -> usize {
return calcExactDecodedSizeWithAlphabet(encoded, standard_alphabet);
}
pub fn calcExactDecodedSizeWithAlphabet(encoded: []const u8, alphabet: []const u8) -> usize {
assert(alphabet.len == 65);
return calcExactDecodedSizeWithPadChar(encoded, alphabet[64]);
}
pub fn calcExactDecodedSizeWithPadChar(encoded: []const u8, pad_char: u8) -> usize {
var buf_len = encoded.len;
while (buf_len > 0 and encoded[buf_len - 1] == pad_char) {
buf_len -= 1;
}
return (buf_len * 3) / 4;
}
test "base64" {
testBase64();
comptime testBase64();
}
fn testBase64() {
testBase64Case("", "");
testBase64Case("f", "Zg==");
testBase64Case("fo", "Zm8=");
testBase64Case("foo", "Zm9v");
testBase64Case("foob", "Zm9vYg==");
testBase64Case("fooba", "Zm9vYmE=");
testBase64Case("foobar", "Zm9vYmFy");
}
fn testBase64Case(expected_decoded: []const u8, expected_encoded: []const u8) {
const calculated_decoded_len = calcExactDecodedSize(expected_encoded);
assert(calculated_decoded_len == expected_decoded.len);
const calculated_encoded_len = calcEncodedSize(expected_decoded.len);
assert(calculated_encoded_len == expected_encoded.len);
var buf: [100]u8 = undefined;
const actual_decoded = decode(buf[0...], expected_encoded);
assert(actual_decoded.len == expected_decoded.len);
assert(mem.eql(u8, expected_decoded, actual_decoded));
const actual_encoded = encode(buf[0...], expected_decoded);
assert(actual_encoded.len == expected_encoded.len);
assert(mem.eql(u8, expected_encoded, actual_encoded));
}
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