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package read
import (
"bytes"
"encoding/binary"
"codeberg.org/lindenii/furgit/internal/intconv"
objectid "codeberg.org/lindenii/furgit/object/id"
)
func layerLookup(layer *layer, oid objectid.ObjectID) (uint32, bool) {
hashSize := oid.Algorithm().Size()
first := int(oid.RawBytes()[0])
var lo uint32
if first > 0 {
lo = binary.BigEndian.Uint32(layer.chunkOIDFanout[(first-1)*4 : first*4])
}
hi := binary.BigEndian.Uint32(layer.chunkOIDFanout[first*4 : (first+1)*4])
if hi == 0 || lo >= hi {
return 0, false
}
target := oid.RawBytes()
left := int(lo)
right := int(hi) - 1
for left <= right {
mid := left + (right-left)/2
start := mid * hashSize
end := start + hashSize
current := layer.chunkOIDLookup[start:end]
cmp := bytes.Compare(current, target)
switch {
case cmp == 0:
pos, err := intconv.IntToUint32(mid)
if err != nil {
return 0, false
}
return pos, true
case cmp < 0:
left = mid + 1
default:
right = mid - 1
}
}
return 0, false
}
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