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, 7 insertions, 4 deletions

diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index b0e3446..0f03dfe 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -557,7 +557,8 @@ PyCode_Addr2Line(PyCodeObject *co, int addrq)
         addr += *p++;
         if (addr > addrq)
             break;
-        line += *p++;
+        line += (signed char)*p;
+        p++;
     }
     return line;
 }
@@ -592,17 +593,19 @@ _PyCode_CheckLineNumber(PyCodeObject* co, int lasti, PyAddrPair *bounds)
         if (addr + *p > lasti)
             break;
         addr += *p++;
-        if (*p)
+        if ((signed char)*p)
             bounds->ap_lower = addr;
-        line += *p++;
+        line += (signed char)*p;
+        p++;
         --size;
     }
 
     if (size > 0) {
         while (--size >= 0) {
             addr += *p++;
-            if (*p++)
+            if ((signed char)*p)
                 break;
+            p++;
         }
         bounds->ap_upper = addr;
     }