What is the minimum precision allowed for floats.
diep at xs4all.nl
Mon Sep 29 14:57:22 CEST 2008
if i remember well, some GPU's are working internal in 40 bits
32 bits for mantissa and the rest for 'zhe power'.
i'm sure they follow not many conventions, can you confirm that?
I assume 32 bits mantissa allows them to do 16 x 16 bits int
calculations == 32 bits precision (integer).
Very bad for FFT type stuff.
On Sep 29, 2008, at 2:35 PM, Vincent Diepeveen wrote:
> If i may ask, how can you reply before i see my own posting on the
> Yeah it's maximum of factor 2.
> We don't do it in floating point of course which is 2 lousy
> instructions a cycle.
> Let's do it in 64 bits integers @ 3 to 4 instructions a cycle :)
> On Sep 29, 2008, at 2:31 PM, Décio Luiz Gazzoni Filho wrote:
>> On Sep 29, 2008, at 8:59 AM, Vincent Diepeveen wrote:
>>> Nah not factor 100.
>>> After most mathematical calculation you just AND with 0xffffffff
>>> to get 48 bits precision.
>> You'd be right if you were doing integer arithmetic. It's floating
>> point, though, so you have more work to do than just arithmetic
>> and masking: the overhead of doing sign-magnitude calculations on
>> two's complement hardware, lining up the mantissas, adjusting the
>> exponent, rounding, etc. If you want to conform to IEEE 754, it's
>> even harder.
>> Perhaps 100x was exaggerated, but I don't think 10x is far off.
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