Anyone recognise this routine, or can give a summery of it's function.

[bobsobol]

I have a routine which is called regularly in one client, but not in another... it's confusing the operation of the one where it is used, and I'm getting lost in it's logic. I believe it's a standard MS VC RT static routine, though I could be wrong... I have no idea what it is supposed to be doing though.

Here is the routine:-

    MOV EDX,DWORD PTR SS:[ARG.3]
    MOV ECX,DWORD PTR SS:[ARG.1]
    TEST EDX,EDX                 ; Cascaded IF (cases 0..3, 3 exits)
    JE SHORT Jump1
    XOR EAX,EAX
    MOV AL,BYTE PTR SS:[ARG.2]
    PUSH EDI
    MOV EDI,ECX
    CMP EDX,4
    JB SHORT Jump2
    NEG ECX                      ; Default case of cascaded IF
    AND ECX,00000003
    JE SHORT Jump3
    SUB EDX,ECX
Jump4:
    MOV BYTE PTR DS:[EDI],AL
    ADD EDI,1
    SUB ECX,1
    JNE SHORT Jump4
Jump3:
    MOV ECX,EAX
    SHL EAX,8
    ADD EAX,ECX
    MOV ECX,EAX
    SHL EAX,10
    ADD EAX,ECX
    MOV ECX,EDX
    AND EDX,00000003
    SHR ECX,2
    JE SHORT Jump2
    REP STOS DWORD PTR ES:[EDI]
    TEST EDX,EDX
    JE SHORT Jump5
Jump2:
    MOV BYTE PTR DS:[EDI],AL     ; Cases 1, 2, 3 of cascaded IF
    ADD EDI,1
    SUB EDX,1
    JNE SHORT Jump2
Jump5:
    MOV EAX,DWORD PTR SS:[ARG.1]
    POP EDI
    RETN
Jump1:
    MOV EAX,DWORD PTR SS:[ARG.1] ; Case 0 of cascaded
    RETN

I know it's a long shot, and I may be better off asking in a RCE forum, but if someone here has seen this logic in a client and made sense of it, or knows it from MSVC I'd be very greatful if you could untie the knotts in my brain right now.

[MentaL]

[bobsobol]

Okay... I think I'm concluding that this routine resets the state of a block of memory. Seems to set a specified run of bytes to 0x00, but also makes a mess of the registers and I'm not sure why.

A "fastcall function (x byval, y byval, z byval)" one assumes.

---EDIT---

Confirmed:-
void fastcall resetmem (StartAddress as DWord, FillValue as LSB?, RunLength as DWord).