[fpc-pascal] Freepascal Floating Point Issue

[Ralf Quint]

On 8/24/2017 2:45 PM, Ched wrote:
> And under "modern" Windows, the extended type, which is fully
> supported by the FPU, is *degraded* to double. So, I can't do high
> precision computation with fpc even if the native hardware permits
> such computations. I'm glued to XP as the full capabilities of the FPU
> were on the hands of programmers, years ago. 
It's not a problem of "modern" Windows, but a problem of any 64bit x86
OS that in that "long" mode the FPU does NOT support the extended data
type (80 bits, 10 bytes). In 32bit mode, the FPU is using the "old" x87
FP unit on the chip, in 64bit mode, it is using the SSE FP unit, which
doesn't have those 80 bit registers, it's 64 bit only (and several times
faster).
So that you can use that with your Windows XP version is likely due to
the fact that this is a 32bit version, not XP Professional 64 (or
Windows Server 2003 64 for that matter).

There are apparently some ways to enable the FP calculation to use the
x87 FPU and therefor the possibility of those 80 bit registers on Inter
chips (so far), but for one, this runs significantly slower that the SSE
FPU, and then this is apparently not supported by (all) AMD CPUs, so you
are limiting yourself also on which systems your code can run...

Ralf


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