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const std = @import("std");
// TODO(rutgerbrf): simplify the code of the encoder & decoder?
pub const Encoder = struct {
const Self = @This();
out_off: u4 = 0,
buf: u5 = 0,
pub fn write(self: *Self, b: u8, out: []u8) usize {
var i: usize = 0;
var bits_left: u4 = 8;
while (bits_left > 0) {
var space_avail = @truncate(u3, 5 - self.out_off);
var write_bits: u3 = if (bits_left < space_avail) @truncate(u3, bits_left) else space_avail;
bits_left -= write_bits;
var mask: u8 = (@as(u8, 0x01) << write_bits) - 1;
var want: u8 = (b >> @truncate(u3, bits_left)) & mask;
self.buf |= @truncate(u5, want << (space_avail - write_bits));
self.out_off += write_bits;
if (self.out_off == 5) {
if (i >= out.len) break;
out[i] = self.char();
i += 1;
self.out_off = 0;
self.buf = 0;
}
}
return i;
}
fn char(self: *const Self) u8 {
return self.buf + (if (self.buf < 26) @as(u8, 'A') else '2' - 26);
}
};
pub const DecodeError = error{CorruptInputError};
pub const Decoder = struct {
const Self = @This();
out_off: u4 = 0,
buf: u8 = 0,
pub fn read(self: *Self, c: u8) DecodeError!?u8 {
var ret: ?u8 = null;
var decoded_c = try decodeChar(c);
var bits_left: u3 = 5;
while (bits_left > 0) {
var space_avail: u4 = 8 - self.out_off;
var write_bits: u3 = if (bits_left < space_avail) bits_left else @truncate(u3, space_avail);
bits_left -= write_bits;
var mask: u8 = (@as(u8, 0x01) << write_bits) - 1;
var want: u8 = (decoded_c >> bits_left) & mask;
self.buf |= want << @truncate(u3, space_avail - write_bits);
self.out_off += write_bits;
if (self.out_off == 8) {
ret = self.buf;
self.out_off = 0;
self.buf = 0;
}
}
return ret;
}
fn decodeChar(p: u8) DecodeError!u5 {
var value: u5 = 0;
if (p >= 'A' and p <= 'Z') {
value = @truncate(u5, p - @as(u8, 'A'));
} else if (p >= '2' and p <= '9') {
// '2' -> 26
value = @truncate(u5, p - @as(u8, '2') + 26);
} else {
return error.CorruptInputError;
}
return value;
}
};
pub fn encodedLen(src_len: usize) usize {
const src_len_bits = src_len * 8;
return src_len_bits / 5 + (if (src_len_bits % 5 > 0) @as(usize, 1) else 0);
}
pub fn decodedLen(enc_len: usize) usize {
const enc_len_bits = enc_len * 5;
return enc_len_bits / 8;
}
pub fn encode(bs: []const u8, out: []u8) usize {
var e = Encoder{};
var i: usize = 0;
for (bs) |b| {
if (i >= out.len) break;
i += e.write(b, out[i..]);
}
if (e.out_off != 0 and i < out.len) {
out[i] = e.char();
i += 1;
}
return i; // amount of bytes processed
}
pub fn decode(ps: []const u8, out: []u8) DecodeError!usize {
var d = Decoder{};
var i: usize = 0;
for (ps) |p| {
if (i >= out.len) break;
if (try d.read(p)) |b| {
out[i] = b;
i += 1;
}
}
if (d.out_off != 0 and i < out.len) {
out[i] = d.buf;
i += 1;
}
return i; // amount of bytes processed
}
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