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count 64 bits at a time

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This commit is contained in:
Brent Pedersen
2019-09-09 14:04:28 -06:00
parent c2ba0ee144
commit 92f2d68802
1 changed files with 7 additions and 3 deletions
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10
lib/system/sets.nim
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@@ -21,7 +21,7 @@ proc countBits32(n: uint32): int {.compilerproc.} =
v = (v and 0x33333333) + ((v shr 2) and 0x33333333)
result = (((v + (v shr 4) and 0xF0F0F0F) * 0x1010101) shr 24).int
proc countBits64(n: uint64): int {.compilerproc.} =
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)
@@ -30,6 +30,10 @@ proc countBits64(n: uint64): int {.compilerproc.} =
result = ((v * 0x0101010101010101'u64) shr 56'u64).int
proc cardSet(s: NimSet, len: int): int {.compilerproc, inline.} =
for i in 0..<len:
if likely(s[i] == 0): continue
var j = -1
for i in countup(0, len - 8, 8):
inc(result, countBits64((cast[ptr uint64](s[i].unsafeAddr))[]))
j = i + 7
for i in (j+1)..<len:
inc(result, countBits32(uint32(s[i])))