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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
# 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")
# BitReader
type BitReader* = ref object
stream: Stream
bitOffset: int
proc bitReader*(stream: Stream): BitReader =
BitReader(stream: stream, bitOffset: 0)
proc atEnd*(bitReader: BitReader): bool =
bitReader.stream.atEnd()
proc readBits*[T: SomeUnsignedInt](bitReader: BitReader, 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 - bitReader.bitOffset:
result = bitReader.stream.peek(T) shl (targetBitLength - bits - bitReader.bitOffset) shr (targetBitLength - bits)
elif bits == targetBitLength - bitReader.bitOffset:
result = bitReader.stream.read(T) shl (targetBitLength - bits - bitReader.bitOffset) shr (targetBitLength - bits)
else:
let rightBits = targetBitLength - bitReader.bitOffset
let leftBits = bits - rightBits
let right = bitReader.stream.read(T) shr bitReader.bitOffset
let left = bitReader.stream.peek(T) shl (targetBitLength - leftBits) shr (targetBitLength - bits)
result = left or right
bitReader.bitOffset = (bitReader.bitOffset + bits) mod wordBitLength
proc readBool*(bitReader: BitReader): bool =
bitReader.readBits(1, uint8) != 0
proc readSeq*[T: SomeUnsignedInt](bitReader: BitReader, 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 bitReader.atEnd(): return
result.bitLength += chunkBitLength
result.data.add(bitReader.readBits(chunkBitLength, T))
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