Re: Nested loops in MASM32

[BlackVortex]

I guess masm is actually doing all the compares instead of just depending on the Z flag, right ?

(too bored to assemble and disassemble,hehe)

[jj2007]

Thanks, Michael, that you took the time to deliver a concrete basis for arguing. I appreciate.
Here is my version of your code (note that your last manual example was actually not a while but rather a repeat loop).

Code Select Expand

.NOLIST
include \masm32\include\masm32rt.inc
.686
include \masm32\macros\timers.asm
.LISTALL

.code
start:
;==============================================================================

invoke Sleep, 3000
    counter_begin 1000, HIGH_PRIORITY_CLASS
        mov ebx, 100
        .REPEAT
            dec ebx
        .UNTIL Zero? ; not: ebx == 0
    counter_end
    print str$(eax), " - rep loop",13,10

    counter_begin 1000, HIGH_PRIORITY_CLASS
        mov ebx, 100
      @@:
        dec ebx
        jnz @B
    counter_end
    print str$(eax), " - rep manual", 13,10

    xor esi, esi

    counter_begin 1000, HIGH_PRIORITY_CLASS
        mov ebx, 100
          jj = 1
if jj
.Repeat
test esi, esi
.Break .if !Zero?
dec ebx
.Until Zero?
else
        .WHILE ebx
            .BREAK .IF esi
            dec ebx
        .ENDW
endif
    counter_end
    print str$(eax)," - rep2 (ex while)", 13,10

    counter_begin 1000, HIGH_PRIORITY_CLASS
        mov ebx, 100
      @@:
        test esi, esi
        jnz @F
        dec ebx
        jnz @B
      @@:
    counter_end
    print str$(eax)," - rep2, manual", 13,10

    inkey "Press any key to exit..."
    exit

;==============================================================================
end start


Celeron M:

Code Select Expand

121 - rep loop
121 - rep manual
209 - rep2 (ex while)
209 - rep2, manual

Edit: P4:

Code Select Expand

177 - rep loop
177 - rep manual
293 - rep2 (ex while)
293 - rep2, manual

Edit: I took away this one because there was no hand-coded equivalent present

Code Select Expand

    counter_begin 1000, HIGH_PRIORITY_CLASS
        mov ebx, 100
        .WHILE ebx
            dec ebx
        .ENDW
    counter_end
    print str$(eax), " - while loop", 13,10


[jj2007]

But what about the branch prediction hints, when using the conditionals you can't use them, isn't that a performance consideration in some cases ? (I've been reading the GoAsm manual, fisrt time I've heard of these prefixes...)

You could use them by inserting the db xx, but:

Branch hint prefixes
GCC has support for this feature, but it has turned out to not gain
anything and was disabled by default, since branch reordering streamlines
code well enough to match the default predictor behaviour.
Same conclusion was done by other compiler teams too, ICC is not
generating the hints either.

[sinsi]

Try a .while/.repeat loop with multiple .break/.continue options and see what it does. 'dec ebx' isn't a great benchmark...

I'm sure I read somewhere that the branch prefix hints are ignored in the core2 and later, and were a real waste of time (agner maybe?).

You could use them by inserting the db xx

Just use a CS: or DS: prefix, that's all they are.

[hutch--]

JJ,

These will do for satarters.

wordreplace
WordCount
szRemove
szRep
szMonoSpace
StrLen
qssorta
parse_line
ltok
wtok
InString

[jj2007]

JJ,

These will do for satarters.

???

Try a .while/.repeat loop with multiple .break/.continue options and see what it does. 'dec ebx' isn't a great benchmark...

Example?

[sinsi]

>Example?
You are the clock meister, I am the one who doesn't use invoke, much less .while. Some .while/.break code when disassembled is like spaghetti...
Whatever happened to LAMPS? That was always good for a chuckle or two  :bg

[jj2007]

Whatever happened to LAMPS? That was always good for a chuckle or two  :bg

LAMPS work only if the code is different in size, speed, or both. Since apparently nobody is able to find an example where a hand-coded loop is different from its matching high level construct, let alone more efficient, there is no point in applying LAMPs...

[hutch--]

JJ,

While we will happily agree about using .WHILE where it works, the list of library modules were all written with non-standard loop designs and while you could probably cobble together the same algorithms with .REPEAT and .WHILE structured loops, it would be ugly sloppy code that did it.

As usual, horses for courses.