[varLib.builder] Implement building 32bit VarStore

The full optimizer in varLib.varStore still needs to be updated.
But this pretty much enables building 32bit VarStores, even if they
won't be fully optimal.

Part of https://github.com/fonttools/fonttools/issues/2279

Lib/fontTools/varLib/builder.py

@@ -26,39 +26,40 @@ def buildVarRegionList(supports, axisTags):
 	return self
 
 
-def _reorderItem(lst, narrows, zeroes):
+def _reorderItem(lst, mapping):
-	out = []
+	return [lst[i] for i in mapping]
-	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 VarData_calculateNumShorts(self, optimize=False):
 	count = self.VarRegionCount
 	items = self.Item
-	narrows = set(range(count))
+	bit_lengths = [0] * count
-	zeroes = set(range(count))
 	for item in items:
-		wides = [i for i in narrows if not (-128 <= item[i] <= 127)]
+		bl = [(i + (i < -1)).bit_length() for i in item]
-		narrows.difference_update(wides)
+		bit_lengths = [max(*pair) for pair in zip(bl, bit_lengths)]
-		nonzeroes = [i for i in zeroes if item[i]]
+	byte_lengths = [((b + 8) // 8) if b else 0 for b in bit_lengths]
-		zeroes.difference_update(nonzeroes)
+
-		if not narrows and not zeroes:
+	# https://github.com/fonttools/fonttools/issues/2279
-			break
+	longWords = any(b > 2 for b in byte_lengths)
+
 	if optimize:
-		# Reorder columns such that all SHORT columns come before UINT8
+		# Reorder columns such that wider columns come before narrower columns
-		self.VarRegionIndex = _reorderItem(self.VarRegionIndex, narrows, zeroes)
+		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)
+			items[i] = _reorderItem(items[i], mapping)
-		self.NumShorts = count - len(narrows)
+
+	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 = max((i for i,b in enumerate(byte_lengths) if b > 1), default=-1) + 1
-		self.NumShorts = 1+max(wides) if wides else 0
+
 	self.VarRegionCount = len(self.VarRegionIndex)
 	return self