ascii85.dart
2.41 KB
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/*
* Copyright (C) 2017, David PHAM-VAN <dev.nfet.net@gmail.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
part of pdf;
class Ascii85Encoder extends Converter<List<int>, List<int>> {
List<int> convert(List<int> input) {
Uint8List buffer = Uint8List(_maxEncodedLen(input.length) + 2);
var b = 0;
var s = 0;
while (s < input.length) {
buffer[b + 0] = 0;
buffer[b + 1] = 0;
buffer[b + 2] = 0;
buffer[b + 3] = 0;
buffer[b + 4] = 0;
// Unpack 4 bytes into int to repack into base 85 5-byte.
int v = 0;
switch (input.length - s) {
case 3:
v |= input[s + 0] << 24;
v |= input[s + 1] << 16;
v |= input[s + 2] << 8;
break;
case 2:
v |= input[s + 0] << 24;
v |= input[s + 1] << 16;
break;
case 1:
v |= input[s + 0] << 24;
break;
default:
v |= input[s + 0] << 24;
v |= input[s + 1] << 16;
v |= input[s + 2] << 8;
v |= input[s + 3];
}
// Special case: zero (!!!!!) shortens to z.
if (v == 0 && input.length - s >= 4) {
buffer[b] = 122;
b++;
s += 4;
continue;
}
// Otherwise, 5 base 85 digits starting at !.
for (int i = 4; i >= 0; i--) {
buffer[b + i] = 33 + v % 85;
v ~/= 85;
}
// If input was short, discard the low destination bytes.
var m = 5;
if (input.length - s < 4) {
m -= 4 - (input.length - s);
break;
} else {
s += 4;
}
b += m;
}
buffer[b] = 0x7e;
buffer[b + 1] = 0x3e;
return buffer.sublist(0, b + 2);
}
int _maxEncodedLen(int n) => (n + 3) ~/ 4 * 5;
}