From fbc5f37d0b78e83e37678178b4b5bea1b1cd8028 Mon Sep 17 00:00:00 2001
From: Tadge Dryja <tadge@lightning.network>
Date: Mon, 21 Dec 2015 22:36:28 -0500
Subject: [PATCH] remove dependencies on mathematics

---
 revocation/shachain.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/revocation/shachain.go b/revocation/shachain.go
index 52d724ad3..d262a3559 100644
--- a/revocation/shachain.go
+++ b/revocation/shachain.go
@@ -72,6 +72,12 @@ func derive(from, to uint64, startingHash [32]byte) [32]byte {
 
 	numBranches := from ^ to
 	toDerive := uint64(math.Log2(float64(numBranches))) // uh.....
+	// math? floats? nahhh! :) bit-flipp-y way to do it:
+	for toDerive = 0; numBranches>>toDerive > 0; toDerive++ {
+	}
+	// ^^^this rounds up instead of down, may be off by 1?
+	toDerive-- // needed?
+
 	for i := int(toDerive - 1); i >= 0; i-- {
 		if (numBranches>>uint(i))&1 == 1 {
 			// Flip the ith bit, then hash the current state to