Fargusson.Alan wrote:
I suspect you are thinking of the prefix instructions used in the block move.
Or maybe you didn't notice that you can use the prefix instruction. In any
case the block move on Intel is about the same as a move character on the
mainframe.
In the 8086 days it took several clock cycles to do anything. The most
annoying to me was the 60 cycle divide instruction. These days they are much
faster, some instructions being only one clock.
The only operations that I know of that take more instructions on Intel are
decimal arithmetic, which are really bad on Intel.
OTOH Intel easily gives you arbitrarily long decimal (and printable)
numbers:-)
<>
When the PC first came out I taught myself some basic assembler for the x86
chip. One thing that I remember to move 255 bytes from one location to another
I had to set up a count register, source register, and target register. The
move instruction was executed in a loop that decemented/incremented (I don't
remember which) the counter. While I'm sure there is a lot of stuff that
happens at the microcode level of the mainframe, we use one assembler
instruction to move 255 bytes. From what I remember of x86 assembler it took
more instructions to do things than it did on the mainframe. If the the x86
chip were faster than the mainframe's chip, would some of that speed be lost
because it takes more instructions to do the same task?
Let me see. Something like this...
mov si,source
mov di,dest
mov cx,length
shl cx,1
rep movsw
jne xx
movsb
xx:
I've not thought about 32-bit and 64-bit implementations
* S/370
la r0,dest
la r1,destlen
la r14,source
la r15,sourcelen
mvcl r14,r0
Intel may have less object code, depending on how the addresses are
calculated. Implementation speeds will vary on both platforms depending
on actual CPU, and on Intel at least, on the actual RAM fitted to the
machine.
--
Cheers
John
-- spambait
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