Midterm 1 -- Open book section

23 February, 1995

The entire exam is to be turned in at 5:45 PM. Work the closed book section first and turn it in before you consult your books and notes to work on the open book section.

Problem 1 (6 points)

Translate the following expression into RPN:

• (x + y*z)-a*(b+3)

Problem 2 (12 points)

How would you translate the following C statements into the assembly language of a RISC- like computer:

• C := A * B ;
• F := C + D + E ;

You should assume that the RISC-like computer has 32 registers, memory-to-register load/store instructions, and three-register arithmetic instructions.

Problem 3 (6 points)

Show the data dependencies in the following sequence of operations. Assume that the first two registers are the operands and the last register is the destination in which the operation result is stored.

• add R1,R2,R3
• add R4,R4,R5
• add R3,R5,R5
• add R3,R4,R6

Problem 4 (6 points)

How could an instruction that increments a register and then branches if the register is zero be used to efficiently execute FORTRAN DO loops?

Problem 5 (6 points)

The Alpha AXP processor has an instruction s8addl such that

• s8addl Ra,Rb,Rc

sets Rc equal to Ra*8+Rb. Where would an instruction like this be useful?

Problem 6 (6 points)

How can you set bits three to seven of a 32-bit word to zero using standard logical operators?

Problem 7 (6 points)

A computer has 32-bit instructions and 14-bit addresses. If there are 14 two-address instructions, how many one-address instructions can be formulated?

Problem 8 (12 points)

Describe how a loop like the one below can be efficiently executed on a vector processor like a Cray.

     for (i=0; i<698; ++i)
       {
        B[i] = A[i] + A[i+1] ;
        A[i] = s + A[i] ;
       }

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