Updated signature blocksize to square root (I thought I did this already but apparently not)

git-svn-id: http://svn.savannah.nongnu.org/svn/rdiff-backup@621 2b77aa54-bcbc-44c9-a7ec-4f6cf2b41109

trunk/rdiff-backup/CHANGELOG

@@ -7,6 +7,8 @@ mirror_metadata file could become un-synced when a file is deleted
 when rdiff-backup is running and later the directory that file is in
 gets deleted.)
 
+Librsync signature blocksize now based on square root of file length.
+
 
 New in v1.0.0 (2005/08/14)
 --------------------------

trunk/rdiff-backup/rdiff_backup/Rdiff.py

@@ -38,9 +38,9 @@ def find_blocksize(file_len):
 	patching can take a really long time.
 
 	"""
-	if file_len < 1024000: return 512 # set minimum of 512 bytes
-	else: # Split file into about 2000 pieces, rounding to 512
-		return long((file_len/(2000*512))*512)
+	if file_len < 4096: return 64 # set minimum of 64 bytes
+	else: # Use square root, rounding to nearest 16
+		return long(pow(file_len, 0.5)/16)*16
 
 def get_delta_sigfileobj(sig_fileobj, rp_new):
 	"""Like get_delta but signature is in a file object"""