tree c8ef60a075973bfecf6b8e67c6eb8ad40e8f4eae
parent 3747a0f04c1dbe5abb47ce80abea39ed02c01aa2
author Tim Peters <tim.peters@gmail.com> 1029180626 +0000
committer Tim Peters <tim.peters@gmail.com> 1029180626 +0000
HG:extra convert_revision:svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/python/branches/legacy-trunk%4028168

k_mul():  White-box testing turned up that (ah+al)*(bh+bl) can, in rare
cases, overflow the allocated result object by 1 bit.  In such cases,
it would have been brought back into range if we subtracted al*bl and
ah*bh from it first, but I don't want to do that because it hurts cache
behavior.  Instead we just ignore the excess bit when it appears -- in
effect, this is forcing unsigned mod BASE**(asize + bsize) arithmetic
in a case where that doesn't happen all by itself.