1. Problem: Consider the following two SRC code segments for implementing multiplication. Find which one is more efficient in terms of instruction count and execution time.
Program 1: Multiplication by using repeated addition in a for loop
Program 2: Multiplication using sub-routine call
la r5, ; load value of loop
lar r6,mpy ;load address of mpy
lar r7, next ;load address of next
ld r2, b ; load contents of b in r2
ld r3, c ; load contents of c in r3
la r4, ;load 0 in r4
mpy:
brzr r7,r ; jump to next after 5 iteration
add r4,r4,r ;r4 contains r4+c
addi r5,r5, ; decrement index
br r ; loop again
next:
add r4,r4,r ; r4 contains sum of b
st r4, a ;store at address label a
lar r1,mpy ;load address of mpy in r1
la r3, ; load index in r3
ld r4,c ; load contents of c in r4
brl r5, r ; r5 contains PC
add r2,r2,r7 ; r2 contains sum of b & 5c
st r2, a
lar r8,again ;r8 contain again address
again:
brzr r5,r ;exit loop when index is 0
add r7,r7,r4 ; r7 contains r7+c
addi r3,r3, ; decrement index
br r8

2. Solution The instructions in both programs can be divided into 3
types and the respective count of each type is
Number of..
Program 1
Program 2
Data transfer instructions 7 6
Control instructions 2 3
ALSU instructions
IC for program 1 = = 12
IC for program 2 = = 12

3. Solution contd.. For execution time, consider the following SRC
specifications.
ET = IC x CPI x T
ET1= (7x4)+(2x2)+(3x3)
= 41
ET2= (6x4)+(3x2)+(3x3)
= 39
Conclusion:
Although the instruction count for both programs is same, program 2 runs much faster than program 1 due to lesser number of clock cycles required.
Instruction Type
CPI
Control 2
ALSU 3
Data Transfer 4