dualfroz/kelindar-bitmap
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fix: union/xor of different-sized bitmaps drops bits in variadic path

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Or and Xor with extra bitmaps used _or_many/_xor_many, which apply a single
word count to every input. The count came from pointersOf, whose length is
the maximum over the extra slice only and ignores other, so a longer other
lost its tail words. More generally a uniform count cannot combine operands
of different lengths: a longer source is truncated and a shorter one is read
past its end.

Fold each source in with the single-operand SIMD primitive over its own
length, matching the scalar reference in simd_generic.go. Fixes the amd64
accelerated and AVX-512 branches and the arm64 branch.
This commit is contained in:
dualfroz committed 2026-09-06 00:42:23 +02:00
1 parent 831b48a3dd
commit 4c67b4458d
3 files changed
+102 -12
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bitmap_amd64.go
+36 -8
View File
@@ -83,16 +83,30 @@ func (dst *Bitmap) Or(other Bitmap, extra ...Bitmap) {
case 0:
_or(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
default:
vx, max := pointersOf(other, extra)
_or_many(unsafe.Pointer(&(*dst)[0]), vx, dimensionsOf(max, len(extra)+1))
// _or_many uses one word count for every input, so it cannot union
// bitmaps of different lengths. Union each source over its own.
if len(other) > 0 {
_or(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
}
for i := range extra {
if len(extra[i]) > 0 {
_or(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&extra[i][0]), uint64(len(extra[i])))
}
}
}
case isAVX512:
switch len(extra) {
case 0:
_or_avx512(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
default:
vx, max := pointersOf(other, extra)
_or_many_avx512(unsafe.Pointer(&(*dst)[0]), vx, dimensionsOf(max, len(extra)+1))
if len(other) > 0 {
_or_avx512(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
}
for i := range extra {
if len(extra[i]) > 0 {
_or_avx512(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&extra[i][0]), uint64(len(extra[i])))
}
}
}
default:
or(*dst, other, extra)
@@ -113,16 +127,30 @@ func (dst *Bitmap) Xor(other Bitmap, extra ...Bitmap) {
case 0:
_xor(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
default:
vx, max := pointersOf(other, extra)
_xor_many(unsafe.Pointer(&(*dst)[0]), vx, dimensionsOf(max, len(extra)+1))
// _xor_many uses one word count for every input, so it cannot combine
// bitmaps of different lengths. Fold in each source over its own.
if len(other) > 0 {
_xor(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
}
for i := range extra {
if len(extra[i]) > 0 {
_xor(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&extra[i][0]), uint64(len(extra[i])))
}
}
}
case isAVX512:
switch len(extra) {
case 0:
_xor_avx512(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
default:
vx, max := pointersOf(other, extra)
_xor_many_avx512(unsafe.Pointer(&(*dst)[0]), vx, dimensionsOf(max, len(extra)+1))
if len(other) > 0 {
_xor_avx512(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
}
for i := range extra {
if len(extra[i]) > 0 {
_xor_avx512(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&extra[i][0]), uint64(len(extra[i])))
}
}
}
default:
xor(*dst, other, extra)
bitmap_arm64.go
+20 -4
View File
@@ -67,8 +67,16 @@ func (dst *Bitmap) Or(other Bitmap, extra ...Bitmap) {
case 0:
_or(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
default:
vx, max := pointersOf(other, extra)
_or_many(unsafe.Pointer(&(*dst)[0]), vx, dimensionsOf(max, len(extra)+1))
// _or_many uses one word count for every input, so it cannot union
// bitmaps of different lengths. Union each source over its own.
if len(other) > 0 {
_or(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
}
for i := range extra {
if len(extra[i]) > 0 {
_or(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&extra[i][0]), uint64(len(extra[i])))
}
}
}
default:
or(*dst, other, extra)
@@ -89,8 +97,16 @@ func (dst *Bitmap) Xor(other Bitmap, extra ...Bitmap) {
case 0:
_xor(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
default:
vx, max := pointersOf(other, extra)
_xor_many(unsafe.Pointer(&(*dst)[0]), vx, dimensionsOf(max, len(extra)+1))
// _xor_many uses one word count for every input, so it cannot combine
// bitmaps of different lengths. Fold in each source over its own.
if len(other) > 0 {
_xor(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&other[0]), uint64(len(other)))
}
for i := range extra {
if len(extra[i]) > 0 {
_xor(unsafe.Pointer(&(*dst)[0]), unsafe.Pointer(&extra[i][0]), uint64(len(extra[i])))
}
}
}
default:
xor(*dst, other, extra)
bitmap_test.go
+46
View File
@@ -629,3 +629,49 @@ func testTruthTables(t *testing.T) {
assert.Equal(t, 0b0110, int(a[0]))
}
}
func TestOr_ExtraDifferentBitmapSizes(t *testing.T) {
// Ragged inputs: every set bit must survive regardless of which is longest.
var dst Bitmap
dst.Set(1) // word 0
dst.Set(70) // word 1
var other Bitmap
other.Set(3) // word 0
other.Set(200) // word 3, beyond every extra bitmap
var short Bitmap
short.Set(5) // word 0 only
var mid Bitmap
mid.Set(130) // word 2
dst.Or(other, short, mid)
want := []uint32{1, 70, 3, 200, 5, 130}
for _, v := range want {
assert.True(t, dst.Contains(v), "missing bit "+strconv.Itoa(int(v)))
}
assert.Equal(t, len(want), dst.Count())
}
func TestXor_ExtraDifferentBitmapSizes(t *testing.T) {
var dst Bitmap
dst.Set(1)
dst.Set(200) // shared with other, must cancel out
var other Bitmap
other.Set(200) // cancels dst's bit 200
other.Set(201) // survives, beyond every extra bitmap
var short Bitmap
short.Set(5)
dst.Xor(other, short)
assert.True(t, dst.Contains(1))
assert.False(t, dst.Contains(200), "bit 200 should cancel")
assert.True(t, dst.Contains(201), "bit 201 from longer source must survive")
assert.True(t, dst.Contains(5))
assert.Equal(t, 3, dst.Count())
}