ascii85.dart
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/*
* Copyright (C) 2017, David PHAM-VAN <dev.nfet.net@gmail.com>
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// ignore_for_file: omit_local_variable_types
part of pdf;
class Ascii85Encoder extends Converter<Uint8List, Uint8List> {
@override
Uint8List convert(Uint8List input) {
final Uint8List output = Uint8List(_maxEncodedLen(input.length) + 2);
int outputOffset = 0;
int inputOffset = 0;
while (inputOffset < input.length) {
output[outputOffset + 0] = 0;
output[outputOffset + 1] = 0;
output[outputOffset + 2] = 0;
output[outputOffset + 3] = 0;
output[outputOffset + 4] = 0;
// Unpack 4 bytes into int to repack into base 85 5-byte.
int value = 0;
switch (input.length - inputOffset) {
case 3:
value |= input[inputOffset + 0] << 24;
value |= input[inputOffset + 1] << 16;
value |= input[inputOffset + 2] << 8;
break;
case 2:
value |= input[inputOffset + 0] << 24;
value |= input[inputOffset + 1] << 16;
break;
case 1:
value |= input[inputOffset + 0] << 24;
break;
default:
value |= input[inputOffset + 0] << 24;
value |= input[inputOffset + 1] << 16;
value |= input[inputOffset + 2] << 8;
value |= input[inputOffset + 3];
}
// Special case: zero (!!!!!) shortens to z.
if (value == 0 && input.length - inputOffset >= 4) {
output[outputOffset] = 122;
outputOffset++;
inputOffset += 4;
continue;
}
// Otherwise, 5 base 85 digits starting at !.
for (int i = 4; i >= 0; i--) {
output[outputOffset + i] = 33 + value % 85;
value ~/= 85;
}
if (input.length - inputOffset < 4) {
// If input was short, discard the low destination bytes.
outputOffset += input.length - inputOffset + 1;
break;
}
inputOffset += 4;
outputOffset += 5;
}
output[outputOffset] = 0x7e;
output[outputOffset + 1] = 0x3e;
return output.sublist(0, outputOffset + 2);
}
int _maxEncodedLen(int length) => (length + 3) ~/ 4 * 5;
}