x86 convert to lower case assembly

Question

This program is to convert a char pointer into lower case. I\'m using Visual Studio 2010.

This is from another question, but much simpler to read and mo

Answer 1

The problem is, that the OR operator like many others don't allow two memory or constant parameters. That means: The OR operator can only have following parameters:

OR register, memory
OR register, register
OR register, constant

The second problem is, that the OR has to store the result to a register, not to memory. Thats why you get an access violation, when the brackets are set. If you remove the brackets, the parameters are ok, but you don't write your lowercase letter to memory, what you intend to do. So use another register, to copy the letter to, and then use OR. For example:

mov eax, 0          ; zero out the result
mov edi, [token]      ; move the token to search for into EDI 
MOV ecx, 0
LOWERCASE_TOKEN:            ;lowercase the token
MOV ebx, [edi]        ;## Copy the value to another register ##
OR ebx, 20h         ;## and compare now the register and the memory ##    
MOV [edi], ebx      ;##Save back the result ##    
INC ecx    
CMP [edi+ecx],0    
JNZ LOWERCASE_TOKEN    
MOV ecx, 0

That should work^^