Author: Eugene Nalimov
Date: 10:31:46 02/16/00
Go up one level in this thread
On February 16, 2000 at 12:37:00, Christophe Theron wrote:
>On February 16, 2000 at 06:34:30, Tom Kerrigan wrote:
>
>>On February 16, 2000 at 00:26:19, Christophe Theron wrote:
>>
>>>I'm not even sure that this processor really supports clean 64 bits operations.
>>>All the docs I have mention 16 and 32 bits long instructions. How do you perform
>>>a move immediate with a 64 bits value if your instruction length is limited to
>>>32 bits?
>>
>>Move immediates are a little silly on RISC processors...
>>
>>You can't even fill a 32 bit register with a move immediate.
>>
>>-Tom
>
>
>So the compiler has to put the data into a static data area, then produce a
>'move from address' instruction?
>
>That must be a "pleasure" to program this chip in assembly... :(
Usually there are special instructions "load to low N bits", "load to high 32-N
bits", so you can load large literal usingl something like
mov r1, lo(literal)
movhi r1, hi(literal)
which is way faster than going into memory. But on *some* processors (ARM,
IBM/360) yes, you have to go into memory. Usually assembler will do the dirty
job for you, and will translate
mov r1, =L'literal'
into e.g.
mov r1, [pc+label]
...
label: dc =L'literal'
Fortunately, there are not many *really* 32-bit constants in the programs (were
it other way, processors would include instrcution 'load 32-bit value', of
course).
Eugene
>Forgive my ignorance about RISC computers...
>
>
> Christophe
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