MASM for FUN - #0.2 [string reversing]

[hutch--]

JJ,

This is why I don't care all that much in this context. The following example runs at about 2.2 gigabyte a second on my Core2 Quad. Yes there are far faster algos to get string lengths but a tiny one does the job in almost every usable instance.

Timing

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1048576000
1 gigabyte in 469 milliseconds
Press any key to continue ...


Example

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    include \masm32\include\masm32rt.inc
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comment * -----------------------------------------------------
                        Build this  template with
                       "CONSOLE ASSEMBLE AND LINK"
        ----------------------------------------------------- *

    slen PROTO :DWORD

    .code

start:
   
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    call main
    inkey
    exit

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main proc


    LOCAL pMem  :DWORD

    mov pMem, alloc(1024*1024*1001)          ; 1001 meg

    invoke memfill,pMem,1024*1024*1000,"xxxx"

    invoke GetTickCount
    push eax

    print str$(rv(slen,pMem)),13,10,"1 gigabyte in "

    invoke GetTickCount
    pop ecx
    sub eax, ecx

    print str$(eax)," milliseconds",13,10

    free pMem

    ret

main endp

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OPTION PROLOGUE:NONE
OPTION EPILOGUE:NONE

slen proc pstr:DWORD

    mov ecx, [esp+4]
    mov eax, ecx
    sub eax, 1

  @@:
    add eax, 1
    cmp BYTE PTR [eax], 0
    jne @B

    sub eax, ecx

    ret 4

slen endp

OPTION PROLOGUE:PrologueDef
OPTION EPILOGUE:EpilogueDef

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end start


[lingo]

Old stuff again.. :wink

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64      cycles for RevLingo
..sogla ym gnitset sa hcus ,sesoprup fo yteirav a sevres taht ,gnol sretcarahc 0
01 ,gnirts a si sihT
161     cycles for RevString
This is a string, 100 characters long, that serves a variety of purposes, such a
s testing my algos..
174     cycles for RevString2
..sogla ym gnitset sa hcus ,sesoprup fo yteirav a sevres taht ,gnol sretcarahc 0
01 ,gnirts a si sihT
162     cycles for RevStr
This is a string, 100 characters long, that serves a variety of purposes, such a
s testing my algos..
216     cycles for szRev
.sogla ym gnitset sa hcus ,sesoprup fo yteirav a sevres taht ,gnol sretcarahc 00
1 ,gnirts a si sihT.

Sizes:
64      RevString
64      RevString2
65      RevStr
62      szRev
121     RevLingo

--- ok ---

[frktons]

 :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol

I have to confess that...
I'd like some Algos explanation.  Just reading the CODE could take
half of my holydays to figure it out, and not sure about that.
After all I'm just an old slow assembly beginner student  :P

What is the logic behind the routines? Why should they be faster or slower?
What kind of Assembly gems are these? What are their strong points?

:lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol  :lol

I'll try to understand them anyway, but a little help is always welcome  :U

Frank

[hutch--]

Frank,

I have addresses two very simple algo designs, the reverse string algo scans a string to get its length first, then it swaps opposite end pairs until it gets to the middle.

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123456789    ; original
923456781    ; 1st swap
983456721    ; 2nd swap
987456321    ; 3rd pair
987654321    ; reversed string


[frktons]

Frank,

I have addresses two very simple algo designs, the reverse string algo scans a string to get its length first, then it swaps opposite end pairs until it gets to the middle.

Code Select Expand


123456789    ; original
923456781    ; 1st swap
983456721    ; 2nd swap
987456321    ; 3rd pair
987654321    ; reversed string


Thanks Hutch, this is the kind of help I need to direct my eyes
into the routines  :U