Chapter 5, Exercise 11

[Aadeshveer]

Error in solution

• I believe for (c) and (d) part of the problem the answer should be 8 as number of blocks int the grid is 8, however the answer is given to be 128.
• Also for part (f) answer given is 7 operations/20 bytes or 0.7 operations/byte which is inconsistant as $\frac{7}{20} = 0.35$

Proposed solution

• There are 8 versions of variable y_s and b_s[], hence answer for (c) and (d) part must be 8
• for (f) part final answer should be 7 operations/20 bytes or 0.35 operations/byte.

[Kaan-wq]

part f needs correction.

Global memory accesses:
Line 7 : 4 loads from a
Line 12 : 1 load from b[i]
Line 14: 1 store to b[i]

FLOPs:
5 multiplications : 2.5fx[0], 3.7fx[1], 6.3fx[2], 8.5fx[3], y_s*b_s[...]
5 additions : six terms summed which means five + operations

float x[4] is allocated in registers because we use constant indexes and x[some_variable]

Thus we have 10/(6*4) = (approx) 0.42 FLOP/B