Split bitstream into bitreader and bitwriter

7 files changed, 173 insertions, 146 deletions

diff --git a/src/bitreader.nim b/src/bitreader.nim
new file mode 100644
index 0000000..35e9d57
--- /dev/null
+++ b/src/bitreader.nim
@@ -0,0 +1,72 @@
+# "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")
+
+# 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))
diff --git a/src/bitstream.nim b/src/bitstream.nim
deleted file mode 100644
index 81401ce..0000000
--- a/src/bitstream.nim
+++ /dev/null
@@ -1,112 +0,0 @@
-# "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])
diff --git a/src/bitwriter.nim b/src/bitwriter.nim
new file mode 100644
index 0000000..aac96f9
--- /dev/null
+++ b/src/bitwriter.nim
@@ -0,0 +1,59 @@
+# "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
+
+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 >= wordBit