The fastest way to clear a buffer

[GregL]

E^cube,

No, you have that backwards E^cube, it was you sending me nasty PMs.  And you got a chance to take a jab at me and you sure took advantage of it didn't you?

[GregL]

Dave,

No problem Dave, I guess I'm just a little on edge tonight, I'm sorry.

[frktons]

give yourself some credit Frank - lol
STOSQ stores a qword (64 bit value)
REP STOSQ is probably fast as hell on 64-bit machines
Jochen showed REP STOSD in his 64-bit example code - that was probably just a small oversight
i am sure he meant REP STOSQ
RtlZeroMemory probably preserves ESI (or RSI), but other than that, it is straightforward
you can assume that the direction flag is clear, as it should be - i am sure RtlZeroMemory also makes that assumption

so....
load the value you want repeated into EAX/RAX
load the repeat count into ECX/RCX
load the address into ESI/RSI
then do the REP STOSD or REP STOSQ

it will be quote fast as long as the address is 4-byte-aligned for 32-bit code or 8-byte-aligned for 64-bit code

Well, Dave I got the 32 bit version of rep stosd, it is not that difficult.
I'm trying to see in 64 bit how it works, and I don't have a clue on how to do it
because I have no 64 bit experience and tools at all.  ::)

So I'm asking somebody to translate and compile in 64 bit mode to test the
performance it gets.

[GregL]

frktons,

I don't think anyone has written timing routines in x64 yet.

[frktons]

frktons,

I don't think anyone has written timing routines in x64 yet.

Time to start? Well, I can be satisfied just seeing how it translate into 64 bit.
It shouldn't be too complex:

Code Select Expand


push edi
mov ecx, 2000
mov edi, offset Dest
mov eax, 20202020h
rep stosd
pop edi

::)

Jochen suggested to start from:

Code Select Expand


    mov rax, 20202020202020202020202020202020h
    mov rdi, offset Dest
    mov rcx, 1000
    rep stosq


And it is quite clear, but what about all the rest of the program?
And moreover is this a legal 64 bit syntax that a 64 bit assembler can assemble?
Which one? JWasm, GoAsm, ML64?

[dedndave]

Code Select Expand

        push    rdi
        mov     rcx,1000
        mov     rdi,offset Dest
        mov     rax,2020202020202020h
        rep     stosq
        pop     rdi
i have no way to test it   :P
JwAsm will assemble it for you
you could clear a larger area using 32-bit and 64-bit, then use a stopwatch   :lol

[frktons]

Code Select Expand

        push    rdi
        mov     rcx,1000
        mov     rdi,offset Dest
        mov     rax,2020202020202020h
        rep     stosq
        pop     rdi
i have no way to test it   :P
JwAsm will assemble it for you

oh, I was writing while you replied. Have a look at my prev post Master.

[dedndave]

i think Jochen has a few too many spaces in there, Frank   :bg
16 spaces = 128 bits in a 64-bit reg
overflow !!! - lol

[frktons]

i think Jochen has a few too many spaces in there, Frank   :bg
16 spaces = 128 bits in a 64-bit reg
overflow !!! - lol

You are right, those were 128 bit xmm registers He used with SSE mnemonics and probably
forgot we were going to native 64 bit registers rxx.
Me too  :P

[jj2007]

2020202020202020h

Folks, if I remember well, Hutch knows a revolutionary mathematical technology to count the spaces in this expression :bg

[hutch--]

 :bg

Huh ?

In my own case "revolutionary" and "mathematical" are not compatible in the same sentence. I freely admit to "Eenie meanie minie moe" technology (fingers) and have to cheat and use computers to add up numbers.

[jj2007]

:bg

Huh ?

In my own case "revolutionary" and "mathematical" are not compatible in the same sentence. I freely admit to "Eenie meanie minie moe" technology (fingers) and have to cheat and use computers to add up numbers.

I meant the "Eenie meanie minie moe" technology. It is quite sufficient to see that there are 8 spaces in 2020202020202020h, not 16 as Dave suspected :wink

[hutch--]

 :bg

Dave is probably cheating and using both hands.

[dedndave]

What about you? I'll give you a starting point:

Code Select Expand

    mov rax, 20202020202020202020202020202020h
    mov rdi, offset buffer
    mov rcx, 1000
    rep stosd

i'd say that either Jochen has had one too many cappuccinos or his space bar is stuck   :lol
note: it should also be STOSQ - not STOSD

http://www.masm32.com/board/index.php?topic=14685.msg119244#msg119244

i cheated and used both hands to create this post

[jj2007]

What about you? I'll give you a starting point:

Code Select Expand

    mov rax, 20202020202020202020202020202020h
    mov rdi, offset buffer
    mov rcx, 1000
    rep stosd

i'd say that either Jochen has had one too many cappuccinos or his space bar is stuck   :lol
note: it should also be STOSQ - not STOSD

Oops, you are right! I had looked at replies 51 & 52 and saw exactly 8 spaces in the code... but that was your code, not mine :red
Apologies :thumbu