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perf(iobufpool): optimize pool index calculations with O(1) bit manipulation #2432

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Merged
jackc merged 1 commit into from
Nov 28, 2025
Merged

perf(iobufpool): optimize pool index calculations with O(1) bit manipulation #2432

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38 changes: 23 additions & 15 deletions internal/iobufpool/iobufpool.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,10 @@
// an allocation is purposely not documented. https://github.com/golang/go/issues/16323
package iobufpool

import "sync"
import (
"math/bits"
"sync"
)

const minPoolExpOf2 = 8

Expand Down Expand Up @@ -37,15 +40,14 @@ func Get(size int) *[]byte {
}

func getPoolIdx(size int) int {
size--
size >>= minPoolExpOf2
i := 0
for size > 0 {
size >>= 1
i++
if size < 2 {
return 0
}

return i
idx := bits.Len(uint(size-1)) - minPoolExpOf2
if idx < 0 {
return 0
}
return idx
}

// Put returns buf to the pool.
Expand All @@ -59,12 +61,18 @@ func Put(buf *[]byte) {
}

func putPoolIdx(size int) int {
minPoolSize := 1 << minPoolExpOf2
for i := range pools {
if size == minPoolSize<<i {
return i
}
// Only exact power-of-2 sizes match pool buckets
if size&(size-1) != 0 {
return -1
}

// Calculate log2(size) using trailing zeros count
exp := bits.TrailingZeros(uint(size))
idx := exp - minPoolExpOf2

if idx < 0 || idx >= len(pools) {
return -1
}

return -1
return idx
}