thanks
mov al, byte ptr[ebx+ecx*edx] should work.
no, it shouldn't work for 100% sure. you can only multiply (read: shift to left) with these immediates: 1 2 4 and 8
ghirai: the byte ptr is redundant, as al is an 8 bit register the assembler knows for sure that you want to use 8 bits, there can be no confusion.
For the assembler ;).
Just to tidy up some of the comments here, MASM is normally written in a form of shorthand which means in most instances that you don't need to specifiy the SIZE of the data in complex memory addressing mode if the assembler already has a way of determining the size. Where this shorthand cannot be used is when there is no way for the assembler to determine the data size.
mov [eax+ecx*4+64], 1 ; error
This is because the complex addressing mode is a memory operand and "1" is an immediate value and neither operand tells thew assembler what SIZE is used. In this context you use the data SIZE specifier to tell the assembler the size.
mov WORD PTR [eax+ecx*4+64], 1
It is the ambiguity that produces the problem and the corresponding requirement to specify the size.