Dalhousie University Faculty of Computer Science

Introduction to Computer Organization with Assembly

Assignment 4       Due: 15 Mar 2021, 11:30pm

(1)     A function with prototype

long decode(long x, long y, long z);

Has the following assembly code from gcc (Note that the line numbers in the first column have no functional value, but are supplied to help):

    x is passed in %rdi, y in %rsi and z in rdx. The return value is stored in % rax. Annotate the assembly code and hence write C code for decode that has the equiv-alent effect to the assembly code.

(2)     • The assembly code below was generated by compiling the C code given below the assembly code.

• Annotate the assembly code and find the values for the missing parts of the C code as indicated by the ‘(i)’ and then answer the following questions:

(a) Which registers hold the values for: x, n, result, and mask? (assume the 64-bit register identifier in each case)

(b) Complete the table below (next page) in order to identify the missing C ex-pressions and the line of assembly code at which each C expression is defined.

    Assembly code for mystery function. Note that the line numbers in the first column have no functional value, but are supplied to help you answer the assignment.

    C code for mystery function. Each instance of (i) represents an unknown variable or expression.

long mystery(long x, long n)

{

    long result = (a) ;

    long mask;

    for (mask = (b); mask (c); mask = (d))

        result = (e) ;

    return result;

}