RPGMaker VX/Ace CE hack

alloc(TypeName,256)
alloc(ByteSize,4)
alloc(PreferedAlignment, 4)
alloc(ConvertRoutine,1024)
alloc(ConvertBackRoutine,1024)

TypeName:
db 'RPG VX type',0

ByteSize:
dd 4

PreferedAlignment:
dd 1


//The convert routine should hold a routine that converts the data to an nteger (in eax)
//function declared as: stdcall int ConvertRoutine(unsigned char *input);

//Note: Keep in mind that this routine can be called by multiple threads at the same time.

ConvertRoutine:
[32-bit]
push ebp
mov ebp,esp
push ecx
mov ecx,[ebp+8]
[/32-bit]

//at this point ecx contains the address where the bytes are stored

//put the bytes into the eax register
mov eax,[ecx] //second fun fact, addressing with 32-bit registers doesn't work in 64-bit, it becomes a 64-bit automatically (most of the time)
shr eax,1 //shift right by 1 bit (divide by 2)

//and now exit the routine
[64-bit]
ret
[/64-bit]
[32-bit]
pop ecx
pop ebp
ret 4
[/32-bit]

//The convert back routine should hold a routine that converts the given integer back to a row of bytes (e.g when the user wats to write a new value)
//function declared as: stdcall void ConvertBackRoutine(int i, unsigned char *output);
ConvertBackRoutine:
[32-bit]
push ebp
mov ebp,esp
push edx //save the registers
push ecx
mov edx,[ebp+0c]
mov ecx,[ebp+08]
[/32-bit]

//at this point edx contains the address to write the value to
//and ecx contains the value

push eax
push edx


mov edx,[edx] //edx now contains the original value
and edx,1 //only save the first bit

mov eax,ecx //eax gets the user input value
shl eax,1 //shift left by 1 bit (multiply by 2)
or eax,edx //add the bits of the original value

pop edx
mov [edx],eax //write the new value into the old value
pop eax

[64-bit]
//everything is back to what it was, so exit
ret
[/64-bit]

[32-bit]
//cleanup first
pop ecx
pop edx
pop ebp
ret 8
[/32-bit]