Nim/lib/system/sets.nim

#
#
#            Nim's Runtime Library
#        (c) Copyright 2012 Andreas Rumpf
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

# set handling

type
  NimSet = array[0..4*2048-1, uint8]

# bitops can't be imported here, therefore the code duplication.

proc countBits32(n: uint32): int {.compilerproc.} =
  # generic formula is from: https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
  var v = uint32(n)
  v = v - ((v shr 1'u32) and 0x55555555'u32)
  v = (v and 0x33333333'u32) + ((v shr 2'u32) and 0x33333333'u32)
  result = (((v + (v shr 4'u32) and 0xF0F0F0F'u32) * 0x1010101'u32) shr 24'u32).int

proc countBits64(n: uint64): int {.compilerproc, inline.} =
  # generic formula is from: https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
  var v = uint64(n)
  v = v - ((v shr 1'u64) and 0x5555555555555555'u64)
  v = (v and 0x3333333333333333'u64) + ((v shr 2'u64) and 0x3333333333333333'u64)
  v = (v + (v shr 4'u64) and 0x0F0F0F0F0F0F0F0F'u64)
  result = ((v * 0x0101010101010101'u64) shr 56'u64).int

proc cardSet(s: NimSet, len: int): int {.compilerproc, inline.} =
  var i = 0
  result = 0
  when defined(x86) or defined(amd64):
    while i < len - 8:
      inc(result, countBits64((cast[ptr uint64](s[i].unsafeAddr))[]))
      inc(i, 8)

  while i < len:
    inc(result, countBits32(uint32(s[i])))
    inc(i, 1)