[Python-checkins] CVS: python/dist/src/Misc NEWS,1.162,1.163

[Tim Peters]

Update of /cvsroot/python/python/dist/src/Misc
In directory usw-pr-cvs1:/tmp/cvs-serv10822/python/dist/src/Misc

Modified Files:
	NEWS 
Log Message:
Blurb about the increased precision of float literals in .pyc/.pyo files.


Index: NEWS
===================================================================
RCS file: /cvsroot/python/python/dist/src/Misc/NEWS,v
retrieving revision 1.162
retrieving revision 1.163
diff -C2 -r1.162 -r1.163
*** NEWS	2001/05/08 04:38:29	1.162
--- NEWS	2001/05/08 15:43:37	1.163
***************
*** 4,7 ****
--- 4,27 ----
  Core
  
+ - Float (and complex) literals in source code were evaluated to full
+   precision only when running from a .py file; the same code loaded from a
+   .pyc (or .pyo) file could suffer numeric differences starting at about the
+   12th significant decimal digit.  For example, on a machine with IEEE-754
+   floating arithmetic,
+ 
+       x = 9007199254740992.0
+       print long(x)
+ 
+   printed 9007199254740992 if run directly from .py, but 9007199254740000
+   if from a compiled (.pyc or .pyo) file.  This was due to marshal using
+   str(float) instead of repr(float) when building code objects.  marshal
+   now uses repr(float) instead, which should reproduce floats to full
+   machine precision (assuming the platform C float<->string I/O conversion
+   functions are of good quality).
+ 
+   This may cause floating-point results to change in some cases, and
+   usually for the better, but may also cause numerically unstable
+   algorithms to break.
+ 
  - Dictionary objects now support the "in" operator: "x in dict" means
    the same as dict.has_key(x).