[OpenBIOS] [RFC 2/3] ppc64: Switch to 64-bit cell size

[Segher Boessenkool]

>>> If I recall correctly what I said, the device-tree property cell 
>>> size is _always_ 32-bit, regardless of what the internal cell size 
>>> is.
>>
>> Don't call that "cell size" :-)  The OF standard calls it "a 32-bit 
>> integer
>> as encoded by encode-int".
>
> There are places where 1275 refers to "cells" in the properties, where 
> it _means_ 32-bit quantities. It's an unfortunate terminology problem.

Only in the actual property names, as far as I know.  Historical 
accident :-)

>>> - The cell size presented to FCode version 2 drivers (plug-in 
>>> cards), which is emulated to be 32 bits.
>>
>> Do you mean the size of (lit) here?  That's 32-bit signed always, 
>> yes.  The
>> FCode cell size is the same as the Forth cell size.  Most FCode 
>> programs
>> written for 32-bit systems work as-is on 64-bit systems; some need 
>> some
>> fixes.  Programs that need 64-bit numbers (for example, for devices 
>> that
>> have 64-bit registers) need some careful coding.
>
> The FCode version 2 interpreter on SPARCs emulates 32-bit FCode by 
> making various operations 32-bit specific. E.g., "0<>" tests only the 
> low-order 32 bits of a cell. The intent was to ensure that 32-bit 
> FCode programs did _not_ need fixes (because we couldn't afford the 
> hassle of forcing everyone to fix them). That has resulted in 
> considerable pain over the years as FCode programs and Forth don't 
> always run the same.

Yeah, it's the worse of two evils, if you ask me.


Segher