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RightTrim function

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Vortex:
RightTrim function to remove the trailing TAB and SPACE characters from a string :


--- Code: ---.386
.model flat,stdcall
option casemap:none

StrLen PROTO :DWORD

.data

ltable db 0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

.code

OPTION PROLOGUE:NONE
OPTION EPILOGUE:NONE

RightTrim PROC _str:DWORD

    mov     eax,DWORD PTR [esp+4]
    invoke  StrLen,eax
    add     eax,DWORD PTR [esp+4]
    mov     ecx,OFFSET ltable
@@:
    sub     eax,1
    movzx   edx,BYTE PTR [eax]
    cmp     BYTE PTR [ecx+edx],1
    je      @b
@@:
    add     eax,1
    mov     BYTE PTR [eax],0
    mov     eax,DWORD PTR [esp+4]
    retn    4

RightTrim ENDP

OPTION PROLOGUE:PROLOGUEDEF
OPTION EPILOGUE:EPILOGUEDEF

END

--- End code ---

Grincheux:
And the same for X64?

Vortex:
Hi Grincheux,

Here is the 64-bit version :


--- Code: ---.model flat,fastcall
option casemap:none

lstrlenA PROTO :QWORD
lstrlen EQU <lstrlenA>

.data

ltable db 0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
       db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

.code

RightTrim PROC _str:DWORD PARMAREA=1*QWORD

LOCAL _rcx:QWORD

    mov     _rcx,rcx
    invoke  lstrlen,rcx
    add     rax,_rcx
    mov     r8,1
    mov     rcx,OFFSET ltable
@@:
    sub     rax,r8
    movzx   rdx,BYTE PTR [rax]
    cmp     BYTE PTR [rcx+rdx],r8b
    je      @b
@@:
    add     rax,r8
    mov     BYTE PTR [rax],0
    mov     rax,_rcx
    ret

RightTrim ENDP
--- End code ---

Testing the function :


--- Code: ---.model flat,fastcall
option casemap:none

includelib  kernel32.lib
includelib  user32.lib
includelib  msvcrt.lib

ExitProcess PROTO :QWORD
RightTrim   PROTO :QWORD
printf      PROTO :QWORD,:VARARG
lstrlenA    PROTO :QWORD

lstrlen EQU <lstrlenA>

.data

teststr     db 'This is a test.        ',0
msg         db 'Length of the string = %u',0

.code

start:

    sub     rsp,8+4*8
   
    invoke  RightTrim,ADDR teststr
           
    invoke  lstrlen,rax
    invoke  printf,ADDR msg,rax
   
    invoke  ExitProcess,0

END start
--- End code ---

Grincheux:
Thank You Vortex. I take, it is better than mine. ;)

Grincheux:
Why do you return a pointer on lTable?
lTable could be got by using VirtualAlloc.

The resulting string cannot be longer than the one passed as an argument.
It can only be shorter or the same size.
So why not use lstrcpy?
The string argument is limited to 256 bytes!
If the string is longer than 256 the function must be called like this RightTrim(&_szString[lstrlen(_szString) - 256]) ;

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