merkle: Proof generation cleanup (#2578)

This change switches internal proof generation code to use uint64, and removes
an unused error return value.

merkle/log_proofs.go

@@ -64,31 +64,31 @@ func CalcConsistencyProofNodeAddresses(size1, size2 int64) ([]NodeFetch, error)
 		return nil, status.Errorf(codes.InvalidArgument, "invalid parameter for consistency proof: size1 %d > size2 %d", size1, size2)
 	}
 
-	return consistencyNodes(size1, size2)
+	return consistencyNodes(uint64(size1), uint64(size2)), nil
 }
 
 // consistencyNodes returns node addresses for the consistency proof between
 // the given tree sizes.
-func consistencyNodes(size1, size2 int64) ([]NodeFetch, error) {
+func consistencyNodes(size1, size2 uint64) []NodeFetch {
 	if size1 == size2 {
-		return []NodeFetch{}, nil
+		return []NodeFetch{}
 	}
 
 	// TODO(pavelkalinnikov): Make the capacity estimate accurate.
-	proof := make([]NodeFetch, 0, bits.Len64(uint64(size2))+1)
+	proof := make([]NodeFetch, 0, bits.Len64(size2)+1)
 
 	// Find the biggest perfect subtree that ends at size1.
-	level := uint(bits.TrailingZeros64(uint64(size1)))
-	index := uint64((size1 - 1)) >> level
+	level := uint(bits.TrailingZeros64(size1))
+	index := (size1 - 1) >> level
 	// If it does not cover the whole size1 tree, add this node to the proof.
 	if index != 0 {
 		n := compact.NewNodeID(level, index)
 		proof = append(proof, NodeFetch{ID: n})
 	}
 
 	// Now append the path from this node to the root of size2.
-	p := proofNodes(index, level, uint64(size2), true)
-	return append(proof, p...), nil
+	p := proofNodes(index, level, size2, true)
+	return append(proof, p...)
 }
 
 // proofNodes returns the node IDs necessary to prove that the (level, index)