Author: Armin Rigo <ar...@tunes.org>
Branch: int-float-list-strategy
Changeset: r78395:e00563965dbd
Date: 2015-07-02 00:10 +0200
http://bitbucket.org/pypy/pypy/changeset/e00563965dbd/
Log: Add comment
diff --git a/pypy/objspace/std/listobject.py b/pypy/objspace/std/listobject.py
--- a/pypy/objspace/std/listobject.py
+++ b/pypy/objspace/std/listobject.py
@@ -1979,6 +1979,13 @@
class IntOrFloatSort(IntOrFloatBaseTimSort):
def lt(self, a, b):
+ # This relies on the fact that casting from a decoded int to a
+ # float is an exact operation. If we had full 64-bit
+ # integers, this cast would loose precision. But this works
+ # because the integers are only 32-bit. This would also work
+ # even if we encoded larger integers: as long as they are
+ # encoded inside a subset of the mantissa of a float, then the
+ # cast-to-float will be exact.
if longlong2float.is_int32_from_longlong_nan(a):
fa = float(longlong2float.decode_int32_from_longlong_nan(a))
else:
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