When writing PUSH instructions, obey requested opcode
Previously fonttools was choosing between the optimal opcode
from PUSHB, NPUSHB, PUSHW, and NPUSHW. We now respect
whatever was requested and err if the format doesn't support
the data.
Morevoer, if the number of numbers to push is more than 255,
we add multiple push instructions to push all the numbers.
Finally, add a new pseudo-opcode "PUSH" that automatically
chooses the best format.
This, by itself, reduces roundtrip noise by not optimizing
the bytecode as it was before. In a followup commit I'll
change the bytecode disassembler to always produce PUSH
in the textual instructions instead of the four variants.
That way, we get both the optimization during assembling,
and reduced noise in XML.
Part of https://github.com/behdad/fonttools/issues/73
diff --git a/Lib/fontTools/ttLib/tables/ttProgram.py b/Lib/fontTools/ttLib/tables/ttProgram.py
index bcd33fa..aa00125 100644
--- a/Lib/fontTools/ttLib/tables/ttProgram.py
+++ b/Lib/fontTools/ttLib/tables/ttProgram.py
@@ -289,7 +289,7 @@
# Unknown instruction
op = int(mnemonic[5:])
push(op)
- elif mnemonic not in ("NPUSHB", "NPUSHW", "PUSHB", "PUSHW"):
+ elif mnemonic not in ("PUSH", "NPUSHB", "NPUSHW", "PUSHB", "PUSHW"):
op, argBits = mnemonicDict[mnemonic]
if len(arg) != argBits:
raise tt_instructions_error("Incorrect number of argument bits (%s[%s])" % (mnemonic, arg))
@@ -305,7 +305,7 @@
m = _tokenRE.match(assembly, pos)
if m is None:
raise tt_instructions_error("Syntax error in TT program (%s)" % assembly[pos:pos+15])
- dummy, mnemonic, arg, number, comment = m.groups()
+ dummy, _mnemonic, arg, number, comment = m.groups()
if number is None and comment is None:
break
pos = m.regs[0][1]
@@ -313,31 +313,37 @@
if comment is not None:
continue
args.append(int(number))
- if max(args) > 255 or min(args) < 0:
- words = 1
- mnemonic = "PUSHW"
- else:
- words = 0
- mnemonic = "PUSHB"
nArgs = len(args)
- if nArgs <= 8:
- op, argBits = streamMnemonicDict[mnemonic]
+ if mnemonic == "PUSH":
+ if nArgs > 8:
+ mnemonic = "N" + mnemonic
+ if max(args) > 255 or min(args) < 0:
+ mnemonic += "W"
+ else:
+ mnemonic += "B"
+
+ words = mnemonic[-1] == "W"
+ op, argBits = streamMnemonicDict[mnemonic]
+ if mnemonic[0] != "N":
+ assert nArgs <= 8, nArgs
op = op + nArgs - 1
+
+ while nArgs:
push(op)
- elif nArgs < 256:
- mnemonic = "N" + mnemonic
- op, argBits = streamMnemonicDict[mnemonic]
- push(op)
- push(nArgs)
- else:
- raise tt_instructions_error("More than 255 push arguments (%s)" % nArgs)
- if words:
- for value in args:
- push((value >> 8) & 0xff)
- push(value & 0xff)
- else:
- for value in args:
- push(value)
+ num = min(nArgs, 255)
+ if mnemonic[0] == "N":
+ push(num)
+ if words:
+ for value in args[:num]:
+ assert -32768 <= value < 32768, "PUSHW value out of range %d" % value
+ push((value >> 8) & 0xff)
+ push(value & 0xff)
+ else:
+ for value in args:
+ assert 0 <= value < 256, "PUSHB value out of range %d" % value
+ push(value)
+ args = args[num:]
+ nArgs -= num
pos = _skipWhite(assembly, pos)
if bytecode: