On 2/15/2010 5:23 PM, Neil Ferguson wrote:
Christoph Groth wrote:
<snipped inconsistent floating point results>
This is on a computer with an Intel Core 2 CPU (I tried several
different variants).
If I take the second (-O1) binary and execute it on an Opteron it
produces the _first_ result. Thus, the same static binary produces
different results on different processors!
This is a hardware-related effect - in a nutshell, it happens because
Intel hardware can extend double-precision floating point operations
to 80 bits internally, whereas AMD hardware usually enforces 64 bits
at all times.
OP didn't indicate that -mfpmath=387 was used for the Intel run, vs.
-mfpmath=sse for the AMD one. It has to be guessed that the rounding
mode was set differently, or (if a 387 build) precision mode was set
differently, or (if an sse build) gradual underflow was set
differently. Both of you are too quick to blame gcc or Intel or AMD for
something which almost certainly stems from other influences.
--
Tim Prince
