Hi
I am new to Pentium assembly programming.
Could you check if I am doing the translation of C to assembly correctly?
Condition: 32-bit addresses, 32 bit integers and 16 bit characters.
char[5] vowels="aeiou";
Translate: vowels db "aeoiu" ; or should it be "vowels dw "aeoiu" ?
How to access vowels[p]? Is it byte[vowels+p*2]? (since characters are 16 bit? )
Many thanks
Yes, the nth element of an array of type T starting at arr is located at memory address arr+n*sizeof(T).
My Intel assembly syntax is a little byte rusty, but word[vowels+p*2] is certainly more correct than byte[vowels+p*2]. You have to multiply by the size of the elements yourself and specify the kind of data read (here, 16-bit quantities).
For the first question, it depends how your assembler interprets "" after db and dw. I do not know about that — I never mixed assembly and 16-bit encodings — but I would assume dw is correct.
Speaking of which, remember to use instruction MOVZX instead of the 16-bit registers that the assembler may let you use. Using the 16-bit registers in 32-bit mode generates long instructions that also execute slowly for a variety of reasons. MOVZX expands the 16-bit value read to occupy an entire 32-bit register, which is the correct way to handle them.