[Radiance-general] compiling Radiance 64-bit?

[Axel Jacobs]

> Correct and radiance gets no where near 2GB. (At least I run out of
> CPU long before the model is that big.)

I totally agree there: It's still the CPU speed that's limiting.

> Why do you think radiance needs to be 64bit?  On both and Sparc and
> the AMD64 the 32bit binaries ran quicker.   Only if it needs to
> address >2G of memory does it *need* to be 64bit.  *Some* programs
> run quicker 64 bit but *most* *don't*, combine with larger executable
> files and increased memory usage I found radiance is best 32 bit.

I am not sure how 'bitty' the floating point values are that RADIANCE
calculates. If they are 64-bit long, then you can actually expect a speed
improvement, me thinks.

> It stands to reason for 64bit programs to be slower because they have
> to use twice the memory to store memory pointers.  Ah you say, doesn't
> 64bit mean it can use 64bit registers for other things? (Like 64bit
> ints and 64bit doubles.)  Well nothing stops that happening in 32bit
> mode if the chip and compilers are well designed, that's what
> sparcv8plus+vis is all about.  32/64bit is the memory address mode
> not the chip registers.  Some say those extra registers are only used
> on AMD64s in 64bit mode; I say I've benchmarks radiance both ways
> and 64 bit was not quicker.

There are benchmarks and there are benchmarks. The only way of finding out
wheter your particular application will benefit from going 64-bit is to
actually test it. Which is what I've done for you.

http://luminance.londonmet.ac.uk/pickup/rad_bench_sempron.html

So sit back, have a cup of coffee, and let the little grey cells do some
pondering.

Cheers

Axel