[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: [f-cpu] (!) a few noteworthy things

> then on bypass the new value will be
>  a) 0xFEDCBA98765432EF (there must be another MUX to select 
> between the old
>      and new value)
>  b) 0x00000000000000EF
>  d) 0x0123456789ABCDEF
>  e) 0x??????????????EF

Assuming you can use 8-bit SIMD instructions on data of the form
0x??????????????xy in order to obtain correct results for the bottom 8 bits,
neglecting the other bits, then you should use option e. 

This is only inadequate in places where the program is converting a short
data type to a longer type (when you need b for unsigned and c for signed),
and this occurs fairly infrequently in program code, so it would be wasteful
to do it every time.

Instead you should have explicit cast instructions for b and c.

Cheers, John

To unsubscribe, send an e-mail to majordomo@seul.org with
unsubscribe f-cpu       in the body. http://f-cpu.seul.org/