MIPS Computer Architecture and Design Homework 3 Solutions - Prof. Vishwani Agrawal, Assignments of Computer Architecture and Organization

Download MIPS Computer Architecture and Design Homework 3 Solutions - Prof. Vishwani Agrawal and more Assignments Computer Architecture and Organization in PDF only on Docsity! ELEC 5200-001/6200-001 Computer Architecture and Design Spring 2009 Homework 3 Solution Assigned 2/9/09, due 2/20/09 Problem 1: For a MIPS computer that has no hardware multiply instruction implemented, write assembly code to multiply integers a and b, which can have any positive or negative values. Answer: The following program multiplies integers a and b. Here $s0 = a, $s1 = b, and the product is placed in $s3. Note that it leaves the arguments a and b unchanged. add $s3, $zero, $zero # initialize running sum $s3 = 0 beq $s0, $zero, fin # finish if argument a = 0 add $t1, $s1, $zero # copy argument b to $t1 repeat beq $t1, $zero, fin # finish when $t1 is 0 bltz $t1, neg # increase $t1 if b is negative addi $t1, $t1, – 1 # else $t1 is decreased by 1 add $s3, $s3, $s0 # compute running sum of $s0 bgez $t1 repeat neg addi $t1, $t1, 1 # $s1 is increased by 1 sub $s3, $s3, $s0 # compute running sum of $s0 blez $t1 repeat fin add $s3, $t1, $zero # $s3 = a * b Problem 2: Write binary machine code for the program of Problem 1. Answer: The machine code is as follows: 000000 00000 00000 10011 00000 100000 add $s3, $zero, $zero 000100 10000 00000 00000 00000 001001 beq $s0, $zero, fin 000000 10001 00000 01001 00000 100000 add $t1, $s1, $zero 000100 01001 00000 00000 00000 000111 repeat beq $t1, $zero, fin 000001 01001 00000 00000 00000 000011 bltz $t1, neg 001000 01001 01001 11111 11111 111111 addi $t1, $t1, – 1 000000 10011 10000 10011 00000 100000 add $s3, $s3, $s0 000001 01001 00001 11111 11111 111011 bgez $t1 repeat 001000 01001 01001 00000 00000 000001 neg addi $t1, $t1, 1 000000 10011 10000 10011 00000 100010 sub $s3, $s3, $s0 000110 01001 00000 11111 11111 111000 blez $t1 repeat 000000 01001 00000 10011 00000 100000 fin add $s3, $t1, $zero Problem 3: Can the code of Problem 1 be used to implement a MIPS pseudoinstruction? Answer: Yes. Only one extra register, $t1, is used in this code. In pseudocode, This register can be replaced by $at.