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→Lab 5
1. Write two different approaches to adjusting the volume of a sequence of sound samples:
* The first one should scale a signed 16-bit integer by multiplying it by a volume scaling factor expressed as a floating point number in the range of 0.0-1.000. This should be implemented as a function that accepts the sample (int16) and scaling factor (float) and returns the scaled sample (int16).* The second one version of the function should do the same thing, using a lookup table (a pre-computed array of all 65536 possible values). The lookup table should be initialized every time a different volume factor is usedobserved. This should be implemented as a drop-in replacement for the function above (same parameters and return value).
2. Test which approach is faster. Control the variables and use a large run of data (at least hundreds millions of samples). Use both [[SPO600 Servers|Xerxes x86 and AarchieAArch64]] systems for testing- DO NOT compare results between the architectures (because they are different classes of systems) but DO compare the relative performance of the algorithms on each architecture. For example, you might note that "Algorithm I is NN% faster on Architecture A, but NN% slower on Architecture B".
3. Blog about your results. Important! -- explain what you're doing so that a reader coming across your blog post understands the context (in other words, don't just jump into a discussion of optimization results -- give your post some context).
=== Things to consider ===
==== Design of Your Test ====
* Most solutions for a problem of this type involve generating a large amount of data in an array, processing that array using the function being evaluated, and then storing that data back into an array. Make sure that you measure the time taken in the test function only -- you need to be able toremove the rest of the processing time from your evaluation.
* You may need to run a very large amount of sample data through the function to be able to detect its performance.
* If you do not use the output from your calculation (e.g., do something with the output array), the compiler may recognize that, and remove the code you're trying to test. Be sure to process the results in some way so that the optimizer preserves the code you want to test. It is a good idea to calculate some sort of verification value to ensure that both approaches generate the same results.
==== Analyzing Results ====
* Does the distribution of data matter?
* If samples are fed at CD rate (44100 samples per second x 2 channels), can both algorithms keep up?
=== Competition ===
* For discussion in class: How fast can you scale 100 500 million int16 PCM sound samples?
=== Tips ===
