co_lnotab supports negative line number delta

Issue #26107: The format of the co_lnotab attribute of code objects changes to
support negative line number delta.

Changes:

* assemble_lnotab(): if line number delta is less than -128 or greater than
  127, emit multiple (offset_delta, lineno_delta) in co_lnotab
* update functions decoding co_lnotab to use signed 8-bit integers

  - dis.findlinestarts()
  - PyCode_Addr2Line()
  - _PyCode_CheckLineNumber()
  - frame_setlineno()

* update lnotab_notes.txt
* increase importlib MAGIC_NUMBER to 3361
* document the change in What's New in Python 3.6
* cleanup also PyCode_Optimize() to use better variable names

1 files changed, 5 insertions, 2 deletions

diff --git a/Lib/dis.py b/Lib/dis.py
index 3540b47..2e80e17 100644
--- a/Lib/dis.py
+++ b/Lib/dis.py
@@ -397,8 +397,8 @@ def findlinestarts(code):
     Generate pairs (offset, lineno) as described in Python/compile.c.
 
     """
-    byte_increments = list(code.co_lnotab[0::2])
-    line_increments = list(code.co_lnotab[1::2])
+    byte_increments = code.co_lnotab[0::2]
+    line_increments = code.co_lnotab[1::2]
 
     lastlineno = None
     lineno = code.co_firstlineno
@@ -409,6 +409,9 @@ def findlinestarts(code):
                 yield (addr, lineno)
                 lastlineno = lineno
             addr += byte_incr
+        if line_incr >= 0x80:
+            # line_increments is an array of 8-bit signed integers
+            line_incr -= 0x100
         lineno += line_incr
     if lineno != lastlineno:
         yield (addr, lineno)