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Fix compile time set cardinality #7558

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Apr 10, 2018
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Fix compile time set cardinality #7558

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25 changes: 25 additions & 0 deletions compiler/bitsets.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ proc bitSetExcl*(x: var TBitSet, elem: BiggestInt)
proc bitSetIn*(x: TBitSet, e: BiggestInt): bool
proc bitSetEquals*(x, y: TBitSet): bool
proc bitSetContains*(x, y: TBitSet): bool
proc bitSetCard*(x: TBitSet): BiggestInt
# implementation

proc bitSetIn(x: TBitSet, e: BiggestInt): bool =
Expand Down Expand Up @@ -69,3 +70,27 @@ proc bitSetContains(x, y: TBitSet): bool =
if (x[i] and not y[i]) != int8(0):
return false
result = true

# Number of set bits for all values of int8
const populationCount: array[low(int8)..high(int8), int8] = [
1.int8, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7
]
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@GULPF

  • how was this generated? (i'm assuming not by hand...)
  • could this be generated via CTFE?
  • if not generated by CTFE, at least needs a test that tries all int8 values

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@GULPF GULPF Apr 11, 2018 •
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I generated it with some quick & dirty code that I didn't want to keep around forever. I agree that it would be better to write some proper code and generate it at compile time, since it's now basically impossible to verify it by just reading it. However, it doesn't really make much of a difference. This table only needs to be verified once, because it will never ever change (but as a counter point, I have added hard-to-verify constants that are wrong before).

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ok how about at least adding the quick and dirty code in a comment in that function? better than nothing IMO

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This table only needs to be verified once, because it will never ever change

Unfortunately it wasn't verified at all afaict. :-) Please use compile-time evaluation for this.


proc bitSetCard(x: TBitSet): BiggestInt =
for it in x:
result.inc populationCount[it]
16 changes: 5 additions & 11 deletions compiler/nimsets.nim
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Expand Up @@ -27,7 +27,7 @@ proc intersectSets*(a, b: PNode): PNode
proc symdiffSets*(a, b: PNode): PNode
proc containsSets*(a, b: PNode): bool
proc equalSets*(a, b: PNode): bool
proc cardSet*(s: PNode): BiggestInt
proc cardSet*(a: PNode): BiggestInt
# implementation

proc inSet(s: PNode, elem: PNode): bool =
Expand Down Expand Up @@ -156,16 +156,10 @@ proc deduplicate*(a: PNode): PNode =
toBitSet(a, x)
result = toTreeSet(x, a.typ, a.info)

proc cardSet(s: PNode): BiggestInt =
# here we can do better than converting it into a compact set
# we just count the elements directly
result = 0
for i in countup(0, sonsLen(s) - 1):
if s.sons[i].kind == nkRange:
result = result + getOrdValue(s.sons[i].sons[1]) -
getOrdValue(s.sons[i].sons[0]) + 1
else:
inc(result)
proc cardSet(a: PNode): BiggestInt =
var x: TBitSet
toBitSet(a, x)
result = bitSetCard(x)

proc setHasRange(s: PNode): bool =
if s.kind != nkCurly:
Expand Down
4 changes: 4 additions & 0 deletions tests/sets/tsets.nim
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Expand Up @@ -202,3 +202,7 @@ var
#import compiler.msgs

echo warnUninit in gNotes

# 7555
doAssert {-1.int8, -2, -2}.card == 2
doAssert {1, 2, 2, 3..5, 4..6}.card == 6