What's new in GCC 4.5?

Posted May 18, 2010 16:47 UTC (Tue) by pharm (guest, #22305)
In reply to: What's new in GCC 4.5? by creemj
Parent article: What's new in GCC 4.5?

No, Intel processors can switch between 64-bit & 80-bit floating point register mode. You can use the -mpc option to gcc to force 64-bit floats.

Why people bang on about -ffloat-store instead of pointing people to -mpc64 if they want to truncate floats to 64 bits on Intel platforms I'm not sure.

Check out the FLDCW (Floating Point Load Control Word) instruction for the gory details.

What's new in GCC 4.5?

Posted May 18, 2010 16:50 UTC (Tue) by pharm (guest, #22305) [Link] (1 responses)

Oh wait, I see what you're saying.

I suppose you can set the control word to 53-bit mantissa & copy a value from one FP register to another. That would be a bit slow though.

What's new in GCC 4.5?

Posted May 31, 2010 15:52 UTC (Mon) by Spudd86 (subscriber, #51683) [Link]

Err doesn't setting the control word before doing ANYTHING mean that you'll keep a 53 bit mantissa throughout?