Issue #4258: Make it possible to use 30-bit digits for PyLongs:

 - new configure option --enable-big-digits
 - new structseq sys.int_info giving information about the internal format
By default, 30-bit digits are enabled on 64-bit machines but
disabled on 32-bit machines.

2 files changed, 40 insertions, 0 deletions

diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index a00c516..091b4d6 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -413,6 +413,23 @@ always available.
    same information.
 
 
+.. data:: int_info
+
+   A struct sequence that holds information about Python's
+   internal representation of integers.  The attributes are read only.
+
+   +-------------------------+----------------------------------------------+
+   | attribute               | explanation                                  |
+   +=========================+==============================================+
+   | :const:`bits_per_digit` | number of bits held in each digit.  Python   |
+   |                         | integers are stored internally in base       |
+   |                         | ``2**int_info.bits_per_digit``               |
+   +-------------------------+----------------------------------------------+
+   | :const:`sizeof_digit`   | size in bytes of the C type used to          |
+   |                         | represent a digit                            |
+   +-------------------------+----------------------------------------------+
+
+
 .. function:: intern(string)
 
    Enter *string* in the table of "interned" strings and return the interned string
diff --git a/Doc/whatsnew/3.1.rst b/Doc/whatsnew/3.1.rst
index 68a76f3..56e5869 100644
--- a/Doc/whatsnew/3.1.rst
+++ b/Doc/whatsnew/3.1.rst
@@ -87,5 +87,28 @@ Some smaller changes made to the core Python language are:
 
   (Contributed by Fredrik Johansson and Victor Stinner; :issue:`3439`.)
 
+* Integers are now stored internally either in base 2**15 or in base
+  2**30, the base being determined at build time.  Previously, they
+  were always stored in base 2**15.  Using base 2**30 gives
+  significant performance improvements on 64-bit machines, but
+  benchmark results on 32-bit machines have been mixed.  Therefore,
+  the default is to use base 2**30 on 64-bit machines and base 2**15
+  on 32-bit machines; on Unix, there's a new configure option
+  --enable-big-digits that can be used to override this default.
+
+  Apart from the performance improvements this change should be
+  invisible to end users, with one exception: for testing and
+  debugging purposes there's a new structseq ``sys.int_info`` that
+  provides information about the internal format, giving the number of
+  bits per digit and the size in bytes of the C type used to store
+  each digit::
+
+     >>> import sys
+     >>> sys.int_info
+     sys.int_info(bits_per_digit=30, sizeof_digit=4)
+
+
+  (Contributed by Mark Dickinson; :issue:`4258`.)
+
 
 .. ======================================================================