91 lines
2.3 KiB
Nim
91 lines
2.3 KiB
Nim
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import
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bitops2
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type
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Bytes = seq[byte]
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BitSeq* = distinct Bytes
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BitArray*[bits: static int] = object
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bytes*: array[(bits + 7) div 8, byte]
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proc len*(s: BitSeq): int =
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let
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bytesCount = s.Bytes.len
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lastByte = s.Bytes[bytesCount - 1]
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markerPos = log2trunc(lastByte)
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Bytes(s).len * 8 - (8 - markerPos)
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template bytes*(s: BitSeq): untyped =
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Bytes(s)
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proc add*(s: var BitSeq, value: bool) =
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let
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lastBytePos = s.Bytes.len - 1
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lastByte = s.Bytes[lastBytePos]
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if (lastByte and byte(128)) == 0:
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# There is at least one leading zero, so we have enough
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# room to store the new bit
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let markerPos = log2trunc(lastByte)
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s.Bytes[lastBytePos].setBit markerPos, value
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s.Bytes[lastBytePos].raiseBit markerPos + 1
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else:
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s.Bytes[lastBytePos].setBit 7, value
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s.Bytes.add byte(1)
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proc `[]`*(s: BitSeq, pos: Natural): bool {.inline.} =
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doAssert pos < s.len
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s.Bytes.getBit pos
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proc `[]=`*(s: var BitSeq, pos: Natural, value: bool) {.inline.} =
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doAssert pos < s.len
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s.Bytes.setBit pos, value
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proc raiseBit*(s: var BitSeq, pos: Natural) {.inline.} =
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doAssert pos < s.len
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raiseBit s.Bytes, pos
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proc lowerBit*(s: var BitSeq, pos: Natural) {.inline.} =
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doAssert pos < s.len
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lowerBit s.Bytes, pos
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proc init*(T: type BitSeq, len: int): T =
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result = BitSeq newSeq[byte](1 + len div 8)
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Bytes(result).raiseBit len
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proc init*(T: type BitArray): T =
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# The default zero-initializatio is fine
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discard
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template `[]`*(a: BitArray, pos: Natural): bool =
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getBit a.bytes, pos
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template `[]=`*(a: var BitArray, pos: Natural, value: bool) =
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setBit a.bytes, pos, value
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template raiseBit*(a: var BitArray, pos: Natural) =
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raiseBit a.bytes, pos
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template lowerBit*(a: var BitArray, pos: Natural) =
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lowerBit a.bytes, pos
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# TODO: Submit this to the standard library as `cmp`
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# At the moment, it doesn't work quite well because Nim selects
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# the generic cmp[T] from the system module instead of choosing
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# the openarray overload
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proc compareArrays[T](a, b: openarray[T]): int =
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result = cmp(a.len, b.len)
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if result != 0: return
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for i in 0 ..< a.len:
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result = cmp(a[i], b[i])
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if result != 0: return
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template cmp*(a, b: BitSeq): int =
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compareArrays(Bytes a, Bytes b)
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template `==`*(a, b: BitSeq): bool =
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cmp(a, b) == 0
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