On Mon, May 15, 2017 at 7:59 AM, Greg Stark <st...@mit.edu> wrote: > On 13 May 2017 at 10:29, Robert Haas <robertmh...@gmail.com> wrote: >> - Floats. There may be different representations in use on different >> hardware, which could be a problem. Tom didn't answer my question >> about whether any even-vaguely-modern hardware is still using non-IEEE >> floats, which I suspect means that the answer is "no". > > Fwiw the answer to that is certainly no. The only caveat is that some > platforms have not entirely complete implementations of IEEE missing > corner cases such as denormalized values but I don't think that would > be something that would be changed with a different hash function > though.
Well... along with the Intel/IEEE-754 and VAX formats, there is a third floating point format that is/was in widespread use: IBM hex float. It's base 16 rather than base 2, and might be the default on some IBM operating systems for the C float and double types (but fortunately not xlc for AIX or Linux, and I have no clue about i/OS). This is probably irrelevant because it looks like people aren't running PostgreSQL on z/OS right now, but unlike VAXen these systems are alive and well so I just wanted to respond to the implication on this thread that the whole world is a VAX or an IEEE system :-) People really use this... I happen to know a shop that has petabytes of IBM hex float data. (IBM hardware also supports base 10 floats, but they show up as different types in C so not relevant.)  https://en.wikipedia.org/wiki/IBM_Floating_Point_Architecture  https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.1.0/com.ibm.zos.v2r1.cbcux01/flotcop.htm#flotcop  https://www.postgresql.org/message-id/flat/BLU437-SMTP4B3FF36035D8A3C3816D49C160%40phx.gbl -- Thomas Munro http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers