From: Brian Warner <warner@lothar.com>
Date: Thu, 11 Aug 2011 17:53:50 +0000 (-0700)
Subject: fix SHARE_HASH_CHAIN_SIZE computation
X-Git-Tag: trac-5200~4
X-Git-Url: https://git.rkrishnan.org/uri/sub?a=commitdiff_plain;h=eec428ba5f3dd93c653a45e04dcd8274f0a3ce7a;p=tahoe-lafs%2Ftahoe-lafs.git

fix SHARE_HASH_CHAIN_SIZE computation
---

diff --git a/src/allmydata/mutable/layout.py b/src/allmydata/mutable/layout.py
index 02069edd..30116414 100644
--- a/src/allmydata/mutable/layout.py
+++ b/src/allmydata/mutable/layout.py
@@ -548,10 +548,10 @@ MDMFOFFSETS_LENGTH = struct.calcsize(MDMFOFFSETS)
 PRIVATE_KEY_SIZE = 1220
 SIGNATURE_SIZE = 260
 VERIFICATION_KEY_SIZE = 292
-# We know we won't have more than 256 shares, and we know that we won't
-# need to store more than lg 256 of them to validate, so that's our
-# bound. We add 1 to the int cast to round to the next integer.
-SHARE_HASH_CHAIN_SIZE = int(math.log(HASH_SIZE * 256)) + 1
+# We know we won't have more than 256 shares, and we know that we won't need
+# to store more than ln2(256) hash-chain nodes to validate, so that's our
+# bound. Each node requires 2 bytes of node-number plus 32 bytes of hash.
+SHARE_HASH_CHAIN_SIZE = (2+HASH_SIZE)*mathutil.log_ceil(256, 2)
 
 class MDMFSlotWriteProxy:
     implements(IMutableSlotWriter)