1 files changed, 47 insertions, 24 deletions

diff --git a/Lib/fontTools/varLib/builder.py b/Lib/fontTools/varLib/builder.py
index 152336b0..60d7172e 100644
--- a/Lib/fontTools/varLib/builder.py
+++ b/Lib/fontTools/varLib/builder.py
@@ -26,39 +26,54 @@ def buildVarRegionList(supports, axisTags):
 	return self
 
 
-def _reorderItem(lst, narrows, zeroes):
-	out = []
-	count = len(lst)
-	for i in range(count):
-		if i not in narrows:
-			out.append(lst[i])
-	for i in range(count):
-		if i in narrows  and i not in zeroes:
-			out.append(lst[i])
-	return out
+def _reorderItem(lst, mapping):
+	return [lst[i] for i in mapping]
 
 def VarData_calculateNumShorts(self, optimize=False):
 	count = self.VarRegionCount
 	items = self.Item
-	narrows = set(range(count))
-	zeroes = set(range(count))
+	bit_lengths = [0] * count
 	for item in items:
-		wides = [i for i in narrows if not (-128 <= item[i] <= 127)]
-		narrows.difference_update(wides)
-		nonzeroes = [i for i in zeroes if item[i]]
-		zeroes.difference_update(nonzeroes)
-		if not narrows and not zeroes:
-			break
+		# The "+ (i < -1)" magic is to handle two's-compliment.
+		# That is, we want to get back 7 for -128, whereas
+		# bit_length() returns 8. Similarly for -65536.
+		# The reason "i < -1" is used instead of "i < 0" is that
+		# the latter would make it return 0 for "-1" instead of 1.
+		bl = [(i + (i < -1)).bit_length() for i in item]
+		bit_lengths = [max(*pair) for pair in zip(bl, bit_lengths)]
+	# The addition of 8, instead of seven, is to account for the sign bit.
+	# This "((b + 8) >> 3) if b else 0" when combined with the above
+	# "(i + (i < -1)).bit_length()" is a faster way to compute byte-lengths
+	# conforming to:
+	#
+	# byte_length = (0 if i == 0 else
+	#		 1 if -128 <= i < 128 else
+	#		 2 if -65536 <= i < 65536 else
+	#		 ...)
+	byte_lengths = [((b + 8) >> 3) if b else 0 for b in bit_lengths]
+
+	# https://github.com/fonttools/fonttools/issues/2279
+	longWords = any(b > 2 for b in byte_lengths)
+
 	if optimize:
-		# Reorder columns such that all SHORT columns come before UINT8
-		self.VarRegionIndex = _reorderItem(self.VarRegionIndex, narrows, zeroes)
+		# Reorder columns such that wider columns come before narrower columns
+		mapping = []
+		mapping.extend(i for i,b in enumerate(byte_lengths) if b > 2)
+		mapping.extend(i for i,b in enumerate(byte_lengths) if b == 2)
+		mapping.extend(i for i,b in enumerate(byte_lengths) if b == 1)
+
+		byte_lengths = _reorderItem(byte_lengths, mapping)
+		self.VarRegionIndex = _reorderItem(self.VarRegionIndex, mapping)
 		self.VarRegionCount = len(self.VarRegionIndex)
 		for i in range(len(items)):
-			items[i] = _reorderItem(items[i], narrows, zeroes)
-		self.NumShorts = count - len(narrows)
+			items[i] = _reorderItem(items[i], mapping)
+
+	if longWords:
+		self.NumShorts = max((i for i,b in enumerate(byte_lengths) if b > 2), default=-1) + 1
+		self.NumShorts |= 0x8000
 	else:
-		wides = set(range(count)) - narrows
-		self.NumShorts = 1+max(wides) if wides else 0
+		self.NumShorts = max((i for i,b in enumerate(byte_lengths) if b > 1), default=-1) + 1
+
 	self.VarRegionCount = len(self.VarRegionIndex)
 	return self
 
@@ -106,6 +121,14 @@ def buildVarIdxMap(varIdxes, glyphOrder):
 	self.mapping = {g:v for g,v in zip(glyphOrder, varIdxes)}
 	return self
 
+
+def buildDeltaSetIndexMap(varIdxes):
+	self = ot.DeltaSetIndexMap()
+	self.mapping = list(varIdxes)
+	self.Format = 1 if len(varIdxes) > 0xFFFF else 0
+	return self
+
+
 def buildVarDevTable(varIdx):
 	self = ot.Device()
 	self.DeltaFormat = 0x8000