Refactor getSearchRange()

4 files changed, 30 insertions, 36 deletions

diff --git a/Lib/fontTools/ttLib/__init__.py b/Lib/fontTools/ttLib/__init__.py
index 1286765a..546b3271 100644
--- a/Lib/fontTools/ttLib/__init__.py
+++ b/Lib/fontTools/ttLib/__init__.py
@@ -966,3 +966,25 @@ def reorderFontTables(inFile, outFile, tableOrder=None, checkChecksums=False):
 	for tag in sortedTagList(tables, tableOrder):
 		writer[tag] = reader[tag]
 	writer.close()
+
+
+def maxPowerOfTwo(x):
+	"""Return the highest exponent of two, so that
+	(2 ** exponent) <= x.  Return 0 if x is 0.
+	"""
+	exponent = 0
+	while x:
+		x = x >> 1
+		exponent = exponent + 1
+	return max(exponent - 1, 0)
+
+
+def getSearchRange(n, itemSize):
+	"""Calculate searchRange, entrySelector, rangeShift.
+	"""
+	# This stuff needs to be stored in the file, because?
+	exponent = maxPowerOfTwo(n)
+	searchRange = (2 ** exponent) * itemSize
+	entrySelector = exponent
+	rangeShift = max(0, n * itemSize - searchRange)
+	return searchRange, entrySelector, rangeShift
diff --git a/Lib/fontTools/ttLib/sfnt.py b/Lib/fontTools/ttLib/sfnt.py
index 95679e99..c65fd28d 100644
--- a/Lib/fontTools/ttLib/sfnt.py
+++ b/Lib/fontTools/ttLib/sfnt.py
@@ -15,6 +15,7 @@ a table's length chages you need to rewrite the whole file anyway.
 from __future__ import print_function, division, absolute_import
 from fontTools.misc.py23 import *
 from fontTools.misc import sstruct
+from fontTools.ttLib import getSearchRange
 import struct
 
 
@@ -116,7 +117,7 @@ class SFNTWriter(object):
 			self.directorySize = sfntDirectorySize
 			self.DirectoryEntry = SFNTDirectoryEntry
 
-			self.searchRange, self.entrySelector, self.rangeShift = getSearchRange(numTables)
+			self.searchRange, self.entrySelector, self.rangeShift = getSearchRange(numTables, 16)
 
 		self.nextTableOffset = self.directorySize + numTables * self.DirectoryEntry.formatSize
 		# clear out directory area
@@ -242,7 +243,7 @@ class SFNTWriter(object):
 		# Haven't debugged.
 		if self.DirectoryEntry != SFNTDirectoryEntry:
 			# Create a SFNT directory for checksum calculation purposes
-			self.searchRange, self.entrySelector, self.rangeShift = getSearchRange(self.numTables)
+			self.searchRange, self.entrySelector, self.rangeShift = getSearchRange(self.numTables, 16)
 			directory = sstruct.pack(sfntDirectoryFormat, self)
 			tables = sorted(self.tables.items())
 			for tag, entry in tables:
@@ -464,29 +465,6 @@ def calcChecksum(data):
 	return value
 
 
-def maxPowerOfTwo(x):
-	"""Return the highest exponent of two, so that
-	(2 ** exponent) <= x
-	"""
-	exponent = 0
-	while x:
-		x = x >> 1
-		exponent = exponent + 1
-	return max(exponent - 1, 0)
-
-
-def getSearchRange(n):
-	"""Calculate searchRange, entrySelector, rangeShift for the
-	sfnt directory. 'n' is the number of tables.
-	"""
-	# This stuff needs to be stored in the file, because?
-	exponent = maxPowerOfTwo(n)
-	searchRange = (2 ** exponent) * 16
-	entrySelector = exponent
-	rangeShift = max(0, n * 16 - searchRange)
-	return searchRange, entrySelector, rangeShift
-
-
 if __name__ == "__main__":
     import doctest
     doctest.testmod()
diff --git a/Lib/fontTools/ttLib/tables/_c_m_a_p.py b/Lib/fontTools/ttLib/tables/_c_m_a_p.py
index a3fb6ccc..0519e78b 100644
--- a/Lib/fontTools/ttLib/tables/_c_m_a_p.py
+++ b/Lib/fontTools/ttLib/tables/_c_m_a_p.py
@@ -1,6 +1,7 @@
 from __future__ import print_function, division, absolute_import
 from fontTools.misc.py23 import *
 from fontTools.misc.textTools import safeEval, readHex
+from fontTools.ttLib import getSearchRange
 from fontTools.unicode import Unicode
 from . import DefaultTable
 import sys
@@ -699,8 +700,6 @@ class cmap_format_4(CmapSubtable):
 	def compile(self, ttFont):
 		if self.data:
 			return struct.pack(">HHH", self.format, self.length, self.language) + self.data
-
-		from fontTools.ttLib.sfnt import maxPowerOfTwo
 		
 		charCodes = list(self.cmap.keys())
 		lenCharCodes = len(charCodes)
@@ -775,13 +774,10 @@ class cmap_format_4(CmapSubtable):
 		idDelta.append(1)  # 0xffff + 1 == (tadaa!) 0. So this end code maps to .notdef
 		idRangeOffset.append(0)
 		
-		# Insane. 
+		# Insane.
 		segCount = len(endCode)
 		segCountX2 = segCount * 2
-		maxExponent = maxPowerOfTwo(segCount)
-		searchRange = 2 * (2 ** maxExponent)
-		entrySelector = maxExponent
-		rangeShift = max(0, 2 * segCount - searchRange)
+		searchRange, entrySelector, rangeShift = getSearchRange(segCount, 2)
 		
 		charCodeArray = array.array("H", endCode + [0] + startCode)
 		idDeltaArray = array.array("H", idDelta)
diff --git a/Lib/fontTools/ttLib/tables/_k_e_r_n.py b/Lib/fontTools/ttLib/tables/_k_e_r_n.py
index b8e60d39..928298bc 100644
--- a/Lib/fontTools/ttLib/tables/_k_e_r_n.py
+++ b/Lib/fontTools/ttLib/tables/_k_e_r_n.py
@@ -1,6 +1,6 @@
 from __future__ import print_function, division, absolute_import
 from fontTools.misc.py23 import *
-from fontTools.ttLib import sfnt
+from fontTools.ttLib import getSearchRange
 from fontTools.misc.textTools import safeEval, readHex
 from fontTools.misc.fixedTools import fixedToFloat as fi2fl, floatToFixed as fl2fi
 from . import DefaultTable
@@ -116,9 +116,7 @@ class KernTable_format_0(object):
 	
 	def compile(self, ttFont):
 		nPairs = len(self.kernTable)
-		entrySelector = sfnt.maxPowerOfTwo(nPairs)
-		searchRange = (2 ** entrySelector) * 6
-		rangeShift = max(0, (nPairs - (2 ** entrySelector)) * 6)
+		searchRange, entrySelector, rangeShift = getSearchRange(nPairs, 6)
 		data = struct.pack(">HHHH", nPairs, searchRange, entrySelector, rangeShift)
 		
 		# yeehee! (I mean, turn names into indices)