CMPxCHG sample

Here is some sample code (from ~10 years ago) that I created. This demonstrates using some inline assembly code concerning CMPXCHG, within the Pelles C.
I’ve included the 8-bit, 16-bit, & 32-bit flavors for CMPXCHG:
// Sorry, yet the text formatting may look lousy on a // smartphone .

typedef unsigned int ui;

// reference : http://faydoc.tripod.com/cpu/cmpxchg.htm
//
//  This atomic functtion returns the ZF,   (ZF = result of comparison).
//  -------- How it works :: --------
//  "expected" is stored into AL,  (=8 bits)
//  then compare AL with "mem".
//  If equal then { ZF=1, and "expected" is stored in mem }
//  else { ZF=0, and AL=MEM (only temporarily) }
//
__declspec(naked) __declspec(dllexport) bool cmpxchg_1(volatile ui *mem, ui expected, ui new)
{
 __asm {
        push ebp
        mov  ebp,esp
        push ebx
        push ecx

        mov ebx,[ebp+8]   ;; EBX points to mem
        mov eax,[ebp+12]  ;; EAX = expected;     Only AL shall be used.
        mov ecx,[ebp+16]  ;; ECX = new;          Only CL shall be used

        lock cmpxchg [ebx],cl

        setz cl           ;; store the zero flag result into CL
        xor eax,eax
        add al,cl         ;; store CL into EAX, and return EAX

        pop ecx
        pop ebx
        pop ebp
        ret 12
       }
}

// reference : http://faydoc.tripod.com/cpu/cmpxchg.htm
//
//  This atomic function returns the ZF,   (ZF = result of comparison).
//  -------- How it works :: --------
//  "expected" is stored into AX,  (=16 bits)
//  then compare AX with "mem".
//  If equal then { ZF=1, and "expected" is stored in mem }
//  else { ZF=0, and AX=MEM (only temporarily) }
//
 __declspec(naked) __declspec(dllexport) bool cmpxchg_2(volatile ui *mem, ui expected, ui new)
{
 __asm {
        push ebp
        mov  ebp,esp
        push ebx
        push ecx

        mov ebx,[ebp+8]   ;; EBX points to mem
        mov eax,[ebp+12]  ;; EAX = expected;     Only AX shall be used.
        mov ecx,[ebp+16]  ;; ECX = new;          Only CX shall be used

        lock cmpxchg [ebx],cx

        setz cl           ;; store the zero flag result into CL
        xor eax,eax
        add al,cl         ;; store CL into EAX, and return EAX

        pop ecx
        pop ebx
        pop ebp
        ret 12
       }
}


// reference : http://faydoc.tripod.com/cpu/cmpxchg.htm
//
//  This atomic functtion returns the ZF,   (ZF = result of comparison).
//  -------- How it works :: --------
//  "expected" is stored into EAX,  (=32 bits)
//  then compare EAX with "mem".
//  If equal then { ZF=1, and "expected" is stored in mem }
//  else { ZF=0, and EAX=MEM (only temporarily) }
//
 __declspec(naked) __declspec(dllexport) bool cmpxchg_4(volatile ui *mem, ui expected, ui new)
{
 __asm {
        push ebp
        mov  ebp,esp
        push ebx
        push ecx

        mov ebx,[ebp+8]   ;; EBX points to mem
        mov eax,[ebp+12]  ;; EAX = expected;
        mov ecx,[ebp+16]  ;; ECX = new;

        lock cmpxchg [ebx],ecx

        setz cl           ;; store the zero flag result into CL
        xor eax,eax
        add al,cl         ;; store CL into EAX, and return EAX

        pop ecx
        pop ebx
        pop ebp
        ret 12
       }
}