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assemblyx86masm

source BYTE "This is the source string",0 target BYTE SIZEOF source DUP(0),0

What is SIZEOF referring to? Is it referring to the size of the source (lengthOf * TYPE which is equal to number of elements in the array * the size of each element)? Also, can someone explain DUP(0),0? This is referring to Assembly x86 MASM. Thank you

Solution

  • SIZEOF simply denotes the size of a type or structure.

    It refers to whatever you put after the SIZEOF keyword. 

    SIZEOF element     ; refers to a single element in the array.  
SIZEOF wholearray  ; sizeof(element) * number_of_elements_in_array.

    Because it is resolved at compile-time it will only work if the size of an array is static.

    The syntax for DUP is:

    count DUP (initialvalue [[, initialvalue]]...)

10 DUP (0)        ; 10 zero's
2 DUP (3 DUP ("A"), "BC")  ; "AAABCAAABC"

    First you get a repeat count, then the keyword DUP and then a specification of what to repeat in brackets.
    The repeat spec may include additional DUP statements.