improve line parsing, using regex to extract labels

Using a regex to parse each line makes the code easier to read
and reason about. It uses capture groups to extract the exact
substrings we need, removing the need for extra whitespace
trimming and string splitting.

Benchmarking showed that it even performs slightly better on
the ESP32, while raising the committed memory by only 64 extra
bytes of memory compared with the previous algorithm
(measured after garbage collect).

Author: wnienhaus

esp32_ulp/assemble.py

@@ -2,6 +2,7 @@
 ESP32 ULP Co-Processor Assembler
 """
 
+import re
 from . import opcodes
 from .nocomment import remove_comments as do_remove_comments
 from .util import garbage_collect
@@ -91,6 +92,12 @@ def __init__(self, symbols=None, bases=None, globals=None):
         self.symbols = SymbolTable(symbols or {}, bases or {}, globals or {})
         opcodes.symbols = self.symbols  # XXX dirty hack
 
+        # regex for parsing assembly lines
+        # format: [[whitespace]label:][whitespace][opcode[whitespace arg[,arg...]]]
+        # where [] means optional
+        # initialised here once, instead of compiling once per line
+        self.line_regex = re.compile(r'^(\s*([a-zA-Z0-9_$.]+):)?\s*((\S*)\s*(.*))$')
+
     def init(self, a_pass):
         self.a_pass = a_pass
         self.sections = dict(text=[], data=[])
@@ -108,29 +115,14 @@ def parse_line(self, line):
         """
         if not line:
             return
-        has_label = ':' in line
-        if has_label:
-            orig_line = line.strip()
-            label_line = orig_line.split(':', 1)
-            if len(label_line) == 2:
-                label, line = label_line
-            else:  # 1
-                label, line = label_line[0], None
-
-            if label.strip('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_$.'):  # if any chars remain
-                # if label contains other chars than allowed, it's not a label
-                label, line = None, orig_line
-        else:
-            label, line = None, line.lstrip()
-        if not line:
-            opcode, args = None, ()
-        else:
-            opcode_args = line.split(None, 1)
-            if len(opcode_args) == 2:
-                opcode, args = opcode_args
-                args = tuple(arg.strip() for arg in args.split(','))
-            else:  # 1
-                opcode, args = opcode_args[0], ()
+
+        matches = self.line_regex.match(line)
+        label, opcode, args = matches.group(2), matches.group(4), matches.group(5)
+
+        label = label if label else None  # force empty strings to None
+        opcode = opcode if opcode else None  # force empty strings to None
+        args = tuple(arg.strip() for arg in args.split(',')) if args else ()
+
         return label, opcode, args
 
     def split_statements(self, lines):

tests/assemble.py

@@ -60,6 +60,7 @@ def test_parse_labels_correctly():
     https://sourceware.org/binutils/docs/as/Labels.html
     """
     a = Assembler()
+    assert a.parse_line('') is None
     assert a.parse_line('label: .set const, 42') == ('label', '.set', ('const', '42',))
     assert a.parse_line('label:.set const, 42') == ('label', '.set', ('const', '42',))
     assert a.parse_line('label:') == ('label', None, ())
@@ -75,6 +76,7 @@ def test_parse_labels_correctly():
     assert a.parse_line('a_label:') == ('a_label', None, ())
     assert a.parse_line('$label:') == ('$label', None, ())
     assert a.parse_line('.label:') == ('.label', None, ())
+    assert a.parse_line('&label:') == (None, '&label:', ())  # & not a valid char in a label
 
 
 def test_parse():