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# "à-la-gzip" 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
# Stream functions
proc newEIO(msg: string): ref IOError =
new(result)
result.msg = msg
proc read[T](s: Stream, t: typedesc[T]): T =
if readData(s, addr(result), sizeof(T)) != sizeof(T):
raise newEIO("cannot read from stream")
proc peek[T](s: Stream, t: typedesc[T]): T =
if peekData(s, addr(result), sizeof(T)) != sizeof(T):
raise newEIO("cannot read from stream")
# Utils
iterator chunks*(totalBitLength: int, chunkType: typedesc[SomeInteger]): tuple[index: int, chunkBitLength: int] =
let chunkBitLength = sizeof(chunkType) * wordBitLength
let wordCount = totalBitLength div chunkBitLength
for i in 0..<(wordCount): yield (i, chunkBitLength)
let remainder = totalBitLength mod chunkBitLength
if remainder > 0: yield (wordCount, remainder)
# BitStream
type BitStream* = ref object
stream: Stream
bitOffset: int
writeBuffer: uint8
proc bitStream*(stream: Stream): BitStream =
BitStream(stream: stream, bitOffset: 0, writeBuffer: 0)
proc flush*(bitStream: BitStream) =
if bitStream.bitOffset == 0: return
bitStream.stream.write(bitStream.writeBuffer)
bitStream.stream.flush()
(bitStream.bitOffset, bitStream.writeBuffer) = (0, 0'u8)
proc atEnd*(bitStream: BitStream): bool =
bitStream.stream.atEnd()
proc readBits*[T: SomeUnsignedInt](bitStream: BitStream, bits: int, to: typedesc[T]): T =
let targetBitLength = sizeof(T) * wordBitLength
if bits < 0 or bits > targetBitLength:
raise newException(RangeError, "invalid bit length")
elif bits == 0:
result = 0
elif bits < targetBitLength - bitStream.bitOffset:
result = bitStream.stream.peek(T) shl (targetBitLength - bits - bitStream.bitOffset) shr (targetBitLength - bits)
elif bits == targetBitLength - bitStream.bitOffset:
result = bitStream.stream.read(T) shl (targetBitLength - bits - bitStream.bitOffset) shr (targetBitLength - bits)
else:
let rightBits = targetBitLength - bitStream.bitOffset
let leftBits = bits - rightBits
let right = bitStream.stream.read(T) shr bitStream.bitOffset
let left = bitStream.stream.peek(T) shl (targetBitLength - leftBits) shr (targetBitLength - bits)
result = left or right
bitStream.bitOffset = (bitStream.bitOffset + bits) mod wordBitLength
proc readBool*(bitStream: BitStream): bool =
bitStream.readBits(1, uint8) != 0
proc readSeq*[T: SomeUnsignedInt](bitStream: BitStream, bitLength: int, to: typedesc[T]): tuple[bitLength: int, data: seq[T]] =
result = (0, newSeqOfCap[T](bitLength /^ (sizeof(T) * wordBitLength)))
for _, chunkBitLength in chunks(bitLength, T):
if bitStream.atEnd(): return
result.bitLength += chunkBitLength
result.data.add(bitStream.readBits(chunkBitLength, T))
proc writeBits*(bitStream: BitStream, 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 + bitStream.bitOffset >= wordBitLength:
bitStream.stream.write(truncateToUint8(value shl bitStream.bitOffset) or bitStream.writeBuffer)
bitsToWrite -= wordBitLength - bitStream.bitOffset
(bitStream.bitOffset, bitStream.writeBuffer) = (0, 0'u8)
while bitsToWrite >= wordBitLength:
bitStream.stream.write(truncateToUint8(value shr (bits - bitsToWrite)))
bitsToWrite -= wordBitLength
if bitsToWrite > 0:
let left = truncateToUint8((value shl (valueContainerBitLength - bits)) shr (valueContainerBitLength - bitsToWrite))
bitStream.writeBuffer = (left shl bitStream.bitOffset) or bitStream.writeBuffer
bitStream.bitOffset = (bitStream.bitOffset + bitsToWrite) mod wordBitLength
proc writeBool*(bitStream: BitStream, value: bool) =
bitStream.writeBits(1, value.uint8)
proc writeSeq*[T: SomeUnsignedInt](bitStream: BitStream, bitLength: int, data: seq[T]) =
for i, chunkBitLength in chunks(bitLength, T):
bitStream.writeBits(chunkBitLength, data[i])
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