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https://github.com/status-im/nim-stew.git
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Refactor the bitranges module
* The bit procs defined over number values and openarray are now part of the bitops2 module and use the more traditional LittleEndian indexing. * Added BitSeq and BitArray types as defined in the ETH2 spec.
This commit is contained in:
Zahary Karadjov
parent
f782f0378f
commit
3fce87f0f5
146
stew/bitops2.nim
146
stew/bitops2.nim
@ -25,6 +25,8 @@ const
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template bitsof*(T: typedesc[SomeInteger]): int = 8 * sizeof(T)
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template bitsof*(x: SomeInteger): int = 8 * sizeof(x)
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type BitIndexable = SomeUnsignedInt
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# #### Pure Nim version ####
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func nextPow2Nim(x: SomeUnsignedInt): SomeUnsignedInt =
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@ -394,3 +396,147 @@ func rotateRight*(v: SomeUnsignedInt, amount: SomeInteger):
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const mask = bitsof(v) - 1
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let amount = int(amount and mask)
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(v shr amount) or (v shl ( (-amount) and mask))
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template mostSignificantBit(T: type): auto =
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const res = 1 shl (sizeof(T) * 8 - 1)
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T(res)
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template getBit*(x: BitIndexable, bit: Natural): bool =
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## reads a bit from `x`, assuming 0 to be the position of the
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## least significant bit
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type T = type(x)
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(x and T(0b1 shl bit)) != 0
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template getBitLE*(x: BitIndexable, bit: Natural): bool =
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getBit(x, bit)
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template getBitBE*(x: BitIndexable, bit: Natural): bool =
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## Reads a bit from `x`, assuming 0 to be the position of
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## the most significant bit.
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##
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## This indexing may be natural when you are considering the
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## string representation of a bit field. For example, 72 can
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## be written in binary as 0b01001000. The first bit here is
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## zero, while the second bit is one.
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##
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## Since the string representation will depend on the size of
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## the operand, using `getBitBE` with the same numeric value
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## and a bit position may produce different results depending
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## on the machine type used to store the value. For this reason,
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## this indexing scheme is considered more error-prone and
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## `getBitLE` is considering the default indexing scheme.
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(x and mostSignificantBit(x.type) shr bit) != 0
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proc setBit*(x: var BitIndexable, bit: Natural, val: bool) =
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## writes a bit in `x`, assuming 0 to be the position of the
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## least significant bit
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type T = type(x)
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let mask = T(0b1 shl bit)
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if val:
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x = x or mask
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else:
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x = x and not mask
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proc setBitLE*(x: var BitIndexable, bit: Natural, val: bool) =
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setBit(x, bit, val)
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proc setBitBE*(x: var BitIndexable, bit: Natural, val: bool) =
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## writes a bit in `x`, assuming 0 to be the position of the
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## most significant bit
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let mask = mostSignificantBit(x.type) shr bit
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if val:
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x = x or mask
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else:
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x = x and not mask
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proc raiseBit*(x: var BitIndexable, bit: Natural) =
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## raises bit in `x`, assuming 0 to be the position of the
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## least significant bit
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type T = type(x)
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let mask = T(0b1 shl bit)
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x = x or mask
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proc raiseBitLE*(x: var BitIndexable, bit: Natural) =
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raiseBit(x, bit)
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proc raiseBitBE*(x: var BitIndexable, bit: Natural) =
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## raises a bit in `x`, assuming 0 to be the position of the
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## most significant bit
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type T = type(x)
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let mask = mostSignificantBit(x.type) shr bit
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x = x or mask
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proc lowerBit*(x: var BitIndexable, bit: Natural) =
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## raises bit in a byte, assuming 0 to be the position of the
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## least significant bit
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type T = type(x)
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let mask = T(0b1 shl bit)
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x = x and not mask
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proc lowerBitLE*(x: var BitIndexable, bit: Natural) =
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lowerBit(x, bit)
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proc lowerBitBE*(x: var BitIndexable, bit: Natural) =
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## raises a bit in `x`, assuming 0 to be the position of the
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## most significant bit
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type T = type(x)
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let mask = mostSignificantBit(x.type) shr bit
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x = x and not mask
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template byteIndex(pos: Natural): int =
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pos shr 3 # same as pos div 8
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template bitIndex(pos: Natural): int =
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pos and 0b111 # same as pos mod 8
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proc getBit*(bytes: openarray[byte], pos: Natural): bool {.inline.} =
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getBit(bytes[byteIndex pos], bitIndex pos)
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proc getBitBE*(bytes: openarray[byte], pos: Natural): bool {.inline.} =
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getBitBE(bytes[byteIndex pos], bitIndex pos)
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template getBitLE*(bytes: openarray[byte], pos: Natural): bool =
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getBit(bytes, pos)
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proc setBit*(bytes: var openarray[byte], pos: Natural, value: bool) {.inline.} =
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setBit(bytes[byteIndex pos], bitIndex pos, value)
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proc setBitBE*(bytes: var openarray[byte], pos: Natural, value: bool) {.inline.} =
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setBitBE(bytes[byteIndex pos], bitIndex pos, value)
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template getBitLE*(bytes: var openarray[byte], pos: Natural, value: bool) =
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setBitLE(bytes, pos)
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proc lowerBit*(bytes: var openarray[byte], pos: Natural) {.inline.} =
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lowerBit(bytes[byteIndex pos], bitIndex pos)
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proc lowerBitBE*(bytes: var openarray[byte], pos: Natural) {.inline.} =
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lowerBitBE(bytes[byteIndex pos], bitIndex pos)
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template lowerBitLE*(bytes: var openarray[byte], pos: Natural) =
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lowerBit(bytes, pos)
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proc raiseBit*(bytes: var openarray[byte], pos: Natural) {.inline.} =
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raiseBit(bytes[byteIndex pos], bitIndex pos)
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proc raiseBitBE*(bytes: var openarray[byte], pos: Natural) {.inline.} =
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raiseBitBE(bytes[byteIndex pos], bitIndex pos)
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template raiseBitLE*(bytes: var openarray[byte], pos: Natural) =
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raiseBit(bytes, pos)
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when isMainModule:
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template test() =
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doAssert countOnes(0b01000100'u8) == 2
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doAssert parity(0b00000001'u8) == 1
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doAssert firstOne(0b00000010'u8) == 2
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doAssert firstOne(0'u8) == 0
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doAssert log2trunc(0b01000000'u8) == 6
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doAssert leadingZeros(0b00100000'u8) == 2
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doAssert trailingZeros(0b00100000'u8) == 5
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doAssert leadingZeros(0'u8) == 8
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doAssert trailingZeros(0'u8) == 8
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test()
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static: test()
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90
stew/bitseqs.nim
Normal file
90
stew/bitseqs.nim
Normal file
@ -0,0 +1,90 @@
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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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@ -1,5 +1,5 @@
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import
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typedranges, ptr_arith
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../bitops2, typedranges, ptr_arith
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type
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BitRange* = object
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@ -7,8 +7,6 @@ type
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start: int
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mLen: int
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BitIndexable = SomeUnsignedInt
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template `@`(s, idx: untyped): untyped =
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(when idx is BackwardsIndex: s.len - int(idx) else: int(idx))
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@ -39,103 +37,17 @@ template bits*(bytes: MutByteRange, slice: HSlice): BitRange =
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template bits*(x: BitRange): BitRange = x
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template mostSignificantBit(T: typedesc): auto =
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const res = 1 shl (sizeof(T) * 8 - 1)
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T(res)
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template getBit*(x: BitIndexable, bit: Natural): bool =
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## reads a bit from `x`, assuming 0 to be the position of the
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## most significant bit
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(x and mostSignificantBit(x.type) shr bit) != 0
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template getBitLE*(x: BitIndexable, bit: Natural): bool =
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## reads a bit from `x`, assuming 0 to be the position of the
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## least significant bit
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type T = type(x)
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(x and T(0b1 shl bit)) != 0
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proc setBit*(x: var BitIndexable, bit: Natural, val: bool) =
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## writes a bit in `x`, assuming 0 to be the position of the
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## most significant bit
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let mask = mostSignificantBit(x.type) shr bit
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if val:
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x = x or mask
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else:
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x = x and not mask
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proc setBitLE*(x: var BitIndexable, bit: Natural, val: bool) =
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## writes a bit in `x`, assuming 0 to be the position of the
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## least significant bit
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type T = type(x)
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let mask = 0b1 shl bit
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if val:
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x = x or mask
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else:
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x = x and not mask
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proc raiseBit*(x: var BitIndexable, bit: Natural) =
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## raises a bit in `x`, assuming 0 to be the position of the
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## most significant bit
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type T = type(x)
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let mask = mostSignificantBit(x.type) shr bit
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x = x or mask
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proc lowerBit*(x: var BitIndexable, bit: Natural) =
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## raises a bit in `x`, assuming 0 to be the position of the
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## most significant bit
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type T = type(x)
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let mask = mostSignificantBit(x.type) shr bit
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x = x and not mask
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proc raiseBitLE*(x: var BitIndexable, bit: Natural) =
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## raises bit in `x`, assuming 0 to be the position of the
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## least significant bit
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type T = type(x)
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let mask = 0b1 shl bit
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x = x or mask
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proc lowerBitLE*(x: var BitIndexable, bit: Natural) =
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## raises bit in a byte, assuming 0 to be the position of the
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## least significant bit
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type T = type(x)
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let mask = 0b1 shl bit
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x = x and not mask
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proc len*(r: BitRange): int {.inline.} = r.mLen
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template getAbsoluteBit(bytes, absIdx: untyped): bool =
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## Returns a bit with a position relative to the start of
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## the underlying range. Not to be confused with a position
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## relative to the start of the BitRange (i.e. the two would
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## match only when range.start == 0).
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let
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byteToCheck = absIdx shr 3 # the same as absIdx / 8
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bitToCheck = (absIdx and 0b111)
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getBit(bytes[byteToCheck], bitToCheck)
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template setAbsoluteBit(bytes, absIdx, value) =
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let
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byteToWrite = absIdx shr 3 # the same as absIdx / 8
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bitToWrite = (absIdx and 0b111)
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setBit(bytes[byteToWrite], bitToWrite, value)
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iterator enumerateBits(x: BitRange): (int, bool) =
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var p = x.start
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var i = 0
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let e = x.len
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while i != e:
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yield (i, getAbsoluteBit(x.data, p))
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yield (i, getBitBE(x.data.toOpenArray, p))
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inc p
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inc i
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proc getBit*(bytes: openarray[byte], pos: Natural): bool =
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getAbsoluteBit(bytes, pos)
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proc setBit*(bytes: var openarray[byte], pos: Natural, value: bool) =
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setAbsoluteBit(bytes, pos, value)
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iterator items*(x: BitRange): bool =
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for _, v in enumerateBits(x): yield v
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@ -145,7 +57,7 @@ iterator pairs*(x: BitRange): (int, bool) =
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proc `[]`*(x: BitRange, idx: int): bool {.inline.} =
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doAssert idx < x.len
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let p = x.start + idx
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result = getAbsoluteBit(x.data, p)
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result = getBitBE(x.data.toOpenArray, p)
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proc sliceNormalized(x: BitRange, ibegin, iend: int): BitRange =
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doAssert ibegin >= 0 and
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@ -170,18 +82,7 @@ proc `==`*(a, b: BitRange): bool =
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proc `[]=`*(r: var BitRange, idx: Natural, val: bool) {.inline.} =
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doAssert idx < r.len
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let absIdx = r.start + idx
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setAbsoluteBit(r.data, absIdx, val)
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proc setAbsoluteBit(x: BitRange, absIdx: int, val: bool) {.inline.} =
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## Assumes the destination bit is already zeroed.
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## Works with absolute positions similar to `getAbsoluteBit`
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doAssert absIdx < x.len
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let
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byteToWrite = absIdx shr 3 # the same as absIdx / 8
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bitToWrite = (absIdx and 0b111)
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if val:
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raiseBit x.data[byteToWrite], bitToWrite
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setBitBE(r.data.toOpenArray, absIdx, val)
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proc pushFront*(x: var BitRange, val: bool) =
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doAssert x.start > 0
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@ -203,15 +104,15 @@ proc `&`*(a, b: BitRange): BitRange =
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var bytes = newSeq[byte](totalLen.neededBytes)
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result = bits(bytes, 0, totalLen)
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for i in 0 ..< a.len: result.setAbsoluteBit(i, a[i])
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for i in 0 ..< b.len: result.setAbsoluteBit(i + a.len, b[i])
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for i in 0 ..< a.len: result.data.toOpenArray.setBitBE(i, a[i])
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for i in 0 ..< b.len: result.data.toOpenArray.setBitBE(i + a.len, b[i])
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proc `$`*(r: BitRange): string =
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result = newStringOfCap(r.len)
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for b in r:
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result.add(if b: '1' else: '0')
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for bit in r:
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result.add(if bit: '1' else: '0')
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proc fromBits*(T: typedesc, r: BitRange, offset, num: Natural): T =
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proc fromBits*(T: type, r: BitRange, offset, num: Natural): T =
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doAssert(num <= sizeof(T) * 8)
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# XXX: Nim has a bug that a typedesc parameter cannot be used
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# in a type coercion, so we must define an alias here:
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@ -219,12 +120,12 @@ proc fromBits*(T: typedesc, r: BitRange, offset, num: Natural): T =
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for i in 0 ..< num:
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result = (result shl 1) or TT(r[offset + i])
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proc parse*(T: typedesc[BitRange], s: string): BitRange =
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proc parse*(T: type BitRange, s: string): BitRange =
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var bytes = newSeq[byte](s.len.neededBytes)
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for i, c in s:
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case c
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of '0': discard
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of '1': raiseBit(bytes[i shr 3], i and 0b111)
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of '1': raiseBitBE(bytes, i)
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else: doAssert false
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result = bits(bytes, 0, s.len)
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@ -1,12 +1,54 @@
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import
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random, unittest,
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../../stew/ranges/bitranges
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../../stew/ranges/bitranges, ../../stew/bitseqs
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proc randomBytes(n: int): seq[byte] =
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result = newSeq[byte](n)
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for i in 0 ..< result.len:
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result[i] = byte(rand(256))
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suite "bit sequences":
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test "growing and indexing":
|
||||
var b0 = BitSeq.init(0)
|
||||
check b0.len == 0
|
||||
|
||||
var b10 = BitSeq.init(10)
|
||||
check b10.len == 10
|
||||
|
||||
var b100 = BitSeq.init(100)
|
||||
check b100.len == 100
|
||||
|
||||
var bytes = randomBytes(50)
|
||||
|
||||
var bitArr: BitArray[50]
|
||||
|
||||
for i in 0 ..< bytes.len:
|
||||
let bit = bytes[i] < 128
|
||||
|
||||
b0.add bit
|
||||
|
||||
if i < b10.len:
|
||||
b10[i] = bit
|
||||
else:
|
||||
b10.add bit
|
||||
|
||||
b100[i] = bit
|
||||
bitArr[i] = bit
|
||||
|
||||
check:
|
||||
b0.len == i + 1
|
||||
b10.len == max(i + 1, 10)
|
||||
b100.len == 100
|
||||
|
||||
for i in 0 ..< bytes.len:
|
||||
let bit = bytes[i] < 128
|
||||
|
||||
check:
|
||||
b0[i] == bit
|
||||
b10[i] == bit
|
||||
b100[i] == bit
|
||||
bitArr[i] == bit
|
||||
|
||||
suite "bit ranges":
|
||||
|
||||
test "basic":
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user