Data commit

Task/Bitwise-IO/Nim/bitwise-io.nim

@@ -0,0 +1,96 @@
+type
+  BitWriter * = tuple
+    file: File
+    bits: uint8
+    nRemain: int
+
+  BitReader * = tuple
+    file: File
+    bits: uint8
+    nRemain: int
+    nRead: int
+
+proc newBitWriter * (file: File) : ref BitWriter =
+  result = new BitWriter
+  result.file = file
+  result.bits = 0
+  result.nRemain = 8
+
+proc flushBits (stream : ref BitWriter) =
+  discard stream.file.writeBuffer(stream.bits.addr, 1)
+  stream.nRemain = 8
+  stream.bits = 0
+
+proc write * (stream: ref BitWriter, bits: uint8, nBits: int) =
+  assert(nBits <= 8)
+
+  for ii in countdown((nBits - 1), 0) :
+    stream.bits = (stream.bits shl 1) or ((bits shr ii) and 1)
+    stream.nRemain.dec(1)
+    if stream.nRemain == 0:
+      stream.flushBits
+
+proc flush * (stream: ref BitWriter) =
+  if stream.nRemain < 8:
+    stream.bits = stream.bits shl stream.nRemain
+    stream.flushBits
+
+proc newBitReader * (file: File) : ref BitReader =
+  result = new BitReader
+  result.file = file
+  result.bits = 0
+  result.nRemain = 0
+  result.nRead = 0
+
+proc read * (stream: ref BitReader, nBits: int) : uint8 =
+  assert(nBits <= 8)
+
+  result = 0
+  for ii in 0 ..< nBits :
+    if stream.nRemain == 0:
+      stream.nRead = stream.file.readBuffer(stream.bits.addr, 1)
+      if stream.nRead == 0:
+        break
+      stream.nRemain = 8
+
+    result = (result shl 1) or ((stream.bits shr 7) and 1)
+
+    stream.bits = stream.bits shl 1
+    stream.nRemain.dec(1)
+
+
+when isMainModule:
+  var
+    file: File
+    writer: ref BitWriter
+    reader: ref BitReader
+
+  file = open("testfile.dat", fmWrite)
+  writer = newBitWriter(file)
+
+  for ii in 0 .. 255:
+    writer.write(ii.uint8, 7)
+
+  writer.flush
+  file.close
+
+  var dataCtr = 0
+
+  file = open("testfile.dat", fmRead)
+  reader = newBitReader(file)
+
+  while true:
+    let aByte = reader.read(7)
+
+    if reader.nRead == 0:
+      break
+
+    assert((dataCtr and 0x7f).uint8 == aByte)
+
+    inc dataCtr
+
+  assert(dataCtr == 256)
+
+  file.close
+
+  echo "OK"