feat(subtree): RootHashPadded accepts non-power-of-two leaf counts#127
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The pow2 precondition on RootHashPadded was overly strict. The natural
root produced by BuildMerkleTreeStoreFromBytes already lives at height
ceil(log2(length)) for any length >= 1 because the duplicate-when-odd
rule is applied at every internal level. Self-hashing from there up to
targetHeight composes correctly with the canonical flat merkle tree.
- replace int(math.Log2(float64(length))) with bits.Len(uint(length-1))
so the height calculation is exact for non-power-of-two lengths
- drop the IsPowerOfTwo guard and the now-unused
ErrNotPowerOfTwoLeafCount sentinel
- convert the prior error-path test into an acceptance test plus a
sweep over r in {1,2,3,5,6,7,9,11,13,15,17,21,23,27,31} that proves
equivalence with the canonical flat root
CI's gosec doesn't flag the uint(length-1) conversion because length >= 1 is provable from the preceding early return. nolintlint then reports the //nolint directive as unused. Drop the annotation — the conversion is safe and CI confirms it doesn't need suppression.
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ordishs
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May 20, 2026
go-subtree v1.4.2 relaxes RootHashPadded to accept non-power-of-two leaf counts (bsv-blockchain/go-subtree#127), making the local liftSubtreeRootToTargetHeight / liftRootForTest helpers redundant. - bump github.com/bsv-blockchain/go-subtree from v1.4.1 to v1.4.2 - delete liftSubtreeRootToTargetHeight in model/Block.go; CheckMerkleRoot calls last.RootHashPadded(targetHeight) directly - delete liftRootForTest in util/subtree_merkle_root_equivalence_test.go; the test calls right.RootHashPadded(left.Height) directly - drop the now-unused crypto/sha256 and math/bits imports in both files
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Summary
The pow2 precondition on
RootHashPaddedwas overly strict. The natural root produced byBuildMerkleTreeStoreFromBytesalready lives at heightceil(log2(length))for anylength >= 1because the duplicate-when-odd rule is applied at every internal level. Self-hashing from there up totargetHeightcomposes correctly with the canonical flat merkle tree.Changes
int(math.Log2(float64(length)))withbits.Len(uint(length-1))so the height calculation is exact for non-power-of-two lengths.IsPowerOfTwoguard and the now-unusedErrNotPowerOfTwoLeafCountsentinel from the public API.TestRootHashPadded_NotPowerOfTwoErrors) into an acceptance test that asserts the lifted root matches both the natural root (whentargetHeight == ceil(log2(length))) and the expected self-hashed value one level above.TestRootHashPadded_MatchesFlatTreeForNonPowerOfTwoFinal, a sweep acrossr ∈ {1,2,3,5,6,7,9,11,13,15,17,21,23,27,31}that proves the composed root (complete left + lifted right) equals the canonical flat merkle root for each remainder size.Motivation
This enables teranode PR #909 to delete duplicate lift-helper code (~40 lines across two files) and call
RootHashPaddeddirectly for the legacy-block partitioner's final subtree of arbitrary length.Breaking change?
ErrNotPowerOfTwoLeafCountis removed from the public API. A grep across this repo and teranode shows no other callers; the only test using it has been converted. External consumers (if any) catching this sentinel would need to drop that branch.Test plan
go test -race ./...(all green, including the new sweep test)go vet ./...golangci-lint run ./...(no new issues introduced)