This is the margin of error for the score. In most cases, that is a half of confidence interval. Think about it as if there is a “±” sign between “Score” and “Score error”. In fact, the human-readable log will show that: Result: 1.986 ±(99.9%) 0.009 ops/ns [Average] Statistics: (min, avg, max) = (1.984, 1.986, … Read more
For a 1-by-N array, they are essentially the same. For a multidimensional array M, they can give different results: numel(M) is equivalent to prod(size(M)). length(M) is equivalent to max(size(M)). If M is empty (i.e. any dimension is 0), then length(M) is 0.
String concatenation a + b + c is a very frequent pattern in Java programs, so HotSpot JVM has a special optimization for it: -XX:+OptimizeStringConcat which is ON by default. HotSpot JVM recognizes new StringBuilder().append()…append().toString() pattern in the bytecode and translates it to the optimized machine code without calling actual Java methods and without allocating … Read more
If you are using c++11 or later you could use std::chrono::high_resolution_clock. A simple use case : auto start = std::chrono::high_resolution_clock::now(); … auto elapsed = std::chrono::high_resolution_clock::now() – start; long long microseconds = std::chrono::duration_cast<std::chrono::microseconds>( elapsed).count(); This solution has the advantage of being portable. Beware that micro-benchmarking is hard. It’s very easy to measure the wrong thing (like … Read more
Well, OP’s benchmarking is not the ideal one. Tons of effects need to be mitigated, including warmup, dead code elimination, forking, etc. Luckily, JMH already takes care of many things, and has bindings for both Java and Scala. Please follow the procedures on JMH page to get the benchmark project, then you can transplant the … Read more
Ok, so you want to know how it behaves at the lower level… Let’s have a look at the bytecode then! EDIT : added the generated assembly code for AMD64, at the end. Have a look for some interesting notes. EDIT 2 (re: OP’s “Update 2”): added asm code for Guava’s isPowerOfTwo method as well. … Read more
z = (set((“a”, “b”, “c”)) – set((x, y))).pop() I am assuming that one of the three cases in your code holds. If this is the case, the set set((“a”, “b”, “c”)) – set((x, y)) will consist of a single element, which is returned by pop(). Edit: As suggested by Raymond Hettinger in the comments, you … Read more
It means exactly what it says on the tin can – it’s measuring the performance of something “small”, like a system call to the kernel of an operating system. The danger is that people may use whatever results they obtain from microbenchmarking to dictate optimizations. And as we all know: We should forget about small … Read more
TL;DR: In unoptimized code, if without else seems irrelevantly more efficient but with even the most basic level of optimization enabled the code is basically rewritten to value = condition + 5. I gave it a try and generated the assembly for the following code: int ifonly(bool condition, int value) { value = 5; if … Read more
I’m ignoring the issue that your benchmarking might be flawed, and taking the result at face value. Is it the compiler or is it at the hardware level? That latter, I think: if (a != 0 && b != 0) will compile to 2 memory loads and two conditional branches if (a * b != … Read more