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code cleanup (#10874)

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Arne Döring 2019-03-28 12:32:02 +01:00 • committed by Andreas Rumpf
commit e904b3f952
6 changed files with 48 additions and 61 deletions
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24
lib/pure/bitops.nim
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@ -154,25 +154,13 @@ proc fastlog2_nim(x: uint64): int {.inline, nosideeffect.} =
v = v or v shr 32
result = lookup[(v * 0x03F6EAF2CD271461'u64) shr 58].int
# sets.nim cannot import bitops, but bitops can use include
# system/sets to eleminate code duplication. sets.nim defines defines
# countBits32 and countBits64.
include system/sets
proc countSetBits_nim(n: uint32): int {.inline, noSideEffect.} =
## Counts the set bits in integer. (also called Hamming weight.)
# generic formula is from: https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
var v = uint32(n)
v = v - ((v shr 1) and 0x55555555)
v = (v and 0x33333333) + ((v shr 2) and 0x33333333)
result = (((v + (v shr 4) and 0xF0F0F0F) * 0x1010101) shr 24).int
proc countSetBits_nim(n: uint64): int {.inline, noSideEffect.} =
## Counts the set bits in integer. (also called Hamming weight.)
# 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
template countSetBits_nim(n: uint32): int = countBits32(n)
template countSetBits_nim(n: uint64): int = countBits64(n)
template parity_impl[T](value: T): int =
# formula id from: https://graphics.stanford.edu/%7Eseander/bithacks.html#ParityParallel