zeroshade commented on code in PR #1327:
URL: https://github.com/apache/arrow-go/pull/1327#discussion_r4188646634
##########
arrow/bitutil/bitutil.go:
##########
@@ -112,6 +113,56 @@ func CountSetBits(buf []byte, offset, n int) int {
return count
}
+// BitmapAllSet reports whether all bits in the requested range are set.
+func BitmapAllSet(buf []byte, offset, n int) bool {
Review Comment:
`BitmapAllSet` is a new public API, but its doc is one line. Please state
that `n == 0` returns true for any `buf` and `offset`, and that otherwise `buf`
must cover `offset+n` bits or the function panics — the same contract as
`CountSetBits`.
##########
arrow/bitutil/bitmap_all_set_scan_test.go:
##########
@@ -0,0 +1,108 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package bitutil_test
+
+import (
+ "fmt"
+ "testing"
+
+ "github.com/apache/arrow-go/v18/arrow/bitutil"
+)
+
+func TestBitmapAllSetWordBoundaries(t *testing.T) {
+ for storageOffset := 0; storageOffset < 8; storageOffset++ {
+ for offset := 0; offset < 64; offset++ {
+ for _, n := range []int{1, 7, 8, 63, 64, 65, 511, 512,
513, 1023, 1024, 1025} {
+ storage := make([]byte,
storageOffset+(offset+n+7)/8)
+ bitmap := storage[storageOffset:]
+ // Keep all padding and neighboring bits clear.
+ for i := offset; i < offset+n; i++ {
+ bitutil.SetBit(bitmap, i)
+ }
+ if !bitutil.BitmapAllSet(bitmap, offset, n) {
+ t.Fatalf("all-set range rejected:
storage=%d offset=%d length=%d", storageOffset, offset, n)
+ }
+ for i := offset; i < offset+n; i++ {
+ bitutil.ClearBit(bitmap, i)
+ if bitutil.BitmapAllSet(bitmap, offset,
n) {
+ t.Fatalf("clear bit %d missed:
storage=%d offset=%d length=%d", i, storageOffset, offset, n)
+ }
+ bitutil.SetBit(bitmap, i)
+ }
+ }
+ }
+ }
+}
+
+func BenchmarkBitmapAllSetScan(b *testing.B) {
+ for _, n := range []int{64, 1024, 65536, 1048576} {
+ for _, offset := range []int{0, 3} {
+ for _, pattern := range []string{"all", "first-null",
"last-null"} {
+ b.Run(fmt.Sprintf("bits=%d/offset=%d/%s", n,
offset, pattern), func(b *testing.B) {
+ bitmap := make([]byte, (offset+n+7)/8)
+ for i := range bitmap {
+ bitmap[i] = 0xff
+ }
+ switch pattern {
+ case "first-null":
+ bitutil.ClearBit(bitmap, offset)
+ case "last-null":
+ bitutil.ClearBit(bitmap,
offset+n-1)
+ }
+ want := pattern == "all"
+ b.ReportAllocs()
+ b.ResetTimer()
+ for i := 0; i < b.N; i++ {
Review Comment:
Nit: use `for b.Loop()` and drop `b.ResetTimer()`, matching the PR's other
benchmark and the rest of `arrow/array`.
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