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# gzip-like LZSS compressor
# Copyright (C) 2018 Pacien TRAN-GIRARD
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# This program 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 Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
import streams
import integers
type BitWriter* = ref object
stream: Stream
bitOffset: int
writeBuffer: uint8
proc bitWriter*(stream: Stream): BitWriter =
BitWriter(stream: stream, bitOffset: 0, writeBuffer: 0)
proc flush*(bitWriter: BitWriter) =
if bitWriter.bitOffset == 0: return
bitWriter.stream.write(bitWriter.writeBuffer)
bitWriter.stream.flush()
(bitWriter.bitOffset, bitWriter.writeBuffer) = (0, 0'u8)
proc atEnd*(bitWriter: BitWriter): bool =
bitWriter.stream.atEnd()
proc writeBits*(bitWriter: BitWriter, bits: int, value: SomeUnsignedInt) =
let valueContainerBitLength = sizeof(value) * wordBitLength
if bits < 0 or bits > valueContainerBitLength:
raise newException(RangeError, "invalid bit length")
var bitsToWrite = bits
if bitsToWrite + bitWriter.bitOffset >= wordBitLength:
bitWriter.stream.write(truncateToUint8(value shl bitWriter.bitOffset) or bitWriter.writeBuffer)
bitsToWrite -= wordBitLength - bitWriter.bitOffset
(bitWriter.bitOffset, bitWriter.writeBuffer) = (0, 0'u8)
while bitsToWrite >= wordBitLength:
bitWriter.stream.write(truncateToUint8(value shr (bits - bitsToWrite)))
bitsToWrite -= wordBitLength
if bitsToWrite > 0:
let left = truncateToUint8((value shl (valueContainerBitLength - bits)) shr (valueContainerBitLength - bitsToWrite))
bitWriter.writeBuffer = (left shl bitWriter.bitOffset) or bitWriter.writeBuffer
bitWriter.bitOffset = (bitWriter.bitOffset + bitsToWrite) mod wordBitLength
proc writeBool*(bitWriter: BitWriter, value: bool) =
bitWriter.writeBits(1, value.uint8)
proc writeSeq*[T: SomeUnsignedInt](bitWriter: BitWriter, bitLength: int, data: seq[T]) =
for i, chunkBitLength in chunks(bitLength, T):
bitWriter.writeBits(chunkBitLength, data[i])
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