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Table 2.7: Branch outcomes with a 2-bit prediction scheme
Iteration BHT prediction Actual branch Outcome update
1 11 (Strongly taken) Taken Correct prediction (No update)
2 11 (Strongly taken) Taken Correct prediction (No update)
FOR ONLINE READING ONLY
3 11 (Strongly taken) Taken Correct prediction (No update) Chapter Two: Performance and optimisation of computer processor
4 11 (Strongly taken) Taken Correct prediction (No update)

5 11 (Strongly taken) Taken Correct prediction (No update)
6 11 (Strongly taken) Taken Correct prediction (No update)
7 11 (Strongly taken) Taken Correct prediction (No update)
8 11 (Strongly taken) Taken Correct prediction (No update)
9 11 (Strongly taken) Not taken Incorrect prediction (Update to 10
(Weakly taken))
10 10 (Weakly taken) Taken Correct prediction (Update to 11
(Strongly taken))

2. 2-Bit BHT Simulation: Simulate
Exercise 2.7 on paper the behavior of a 2-bit
1. You are working on a processor Branch History Table (BHT) for the
design that utilizes dynamic provided loop. Assume the initial
branch prediction. The processor BHT prediction state is “Strongly
encounters the following loop code: Not Taken” (00)
for (int i = 0; i < 10; i++) { (a) Create a table with the
following columns: Iteration,
if (i > 5) { Actual Branch, BHT
// Code for the second half of the loop Prediction (before the update),
} and Outcome update (after
execution).
} (b) Fill out the table for the first
(a) Analyse the loop behavior five iterations of the loop.
and identify how many times 3. Based on your simulation in
the conditional branch (“if (i question 2, calculate the prediction
> 5)”) will be taken during a accuracy of the 2-bit BHT for the
single loop iteration. Explain first five iterations of the loop.
your answer. 4. Briefly discuss the impact of branch

(b) Which approach would be prediction accuracy on processor
performance. How can improved
more suitable for the given prediction accuracy benefit real-
loop, and why? world applications?

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Student’s Book Form Five

Computer Science Form 5.indd 107 23/07/2024 12:33