http://bugs.python.org/issue2459 -- speed up loops

Lib/compiler/pyassem.py

 """A flow graph representation for Python bytecode"""
 
 import dis
 import types
 import sys
 
 from compiler import misc
 from compiler.consts \
      import CO_OPTIMIZED, CO_NEWLOCALS, CO_VARARGS, CO_VARKEYWORDS
 
@@ skipping 602 matching lines @@
         self.codeOffset = self.codeOffset + len(args)
 
     def nextLine(self, lineno):
         if self.firstline == 0:
             self.firstline = lineno
             self.lastline = lineno
         else:
             # compute deltas
             addr = self.codeOffset - self.lastoff
             line = lineno - self.lastline
+            abs_line = abs(line)
+            if line >= 0:
+                sign_line = lambda l: l
+            else:
+                sign_line = lambda l: 256 - l
             # Python assumes that lineno always increases with
             # increasing bytecode address (lnotab is unsigned char).
             # Depending on when SET_LINENO instructions are emitted
             # this is not always true.  Consider the code:
             #     a = (1,
             #          b)
             # In the bytecode stream, the assignment to "a" occurs
             # after the loading of "b".  This works with the C Python
             # compiler because it only generates a SET_LINENO instruction
             # for the assignment.
-            if line >= 0:
-                push = self.lnotab.append
-                while addr > 255:
-                    push(255); push(0)
-                    addr -= 255
-                while line > 255:
-                    push(addr); push(255)
-                    line -= 255
-                    addr = 0
-                if addr > 0 or line > 0:
-                    push(addr); push(line)
-                self.lastline = lineno
-                self.lastoff = self.codeOffset
+            push = self.lnotab.append
+            while addr > 255:
+                push(255); push(0)
+                addr -= 255
+            while abs_line > 127:
+                push(addr); push(sign_line(127))
+                abs_line -= 127
+                addr = 0
+            if addr > 0 or abs_line > 0:
+                push(addr); push(sign_line(abs_line))
+            self.lastline = lineno
+            self.lastoff = self.codeOffset
 
     def getCode(self):
         return ''.join(self.code)
 
     def getTable(self):
         return ''.join(map(chr, self.lnotab))
 
 class StackDepthTracker:
     # XXX 1. need to keep track of stack depth on jumps
     # XXX 2. at least partly as a result, this code is broken
@@ skipping 94 matching lines @@
         return -argc
     def BUILD_SLICE(self, argc):
         if argc == 2:
             return -1
         elif argc == 3:
             return -2
     def DUP_TOPX(self, argc):
         return argc
 
 findDepth = StackDepthTracker().findDepth