Posts about PerformanceExercise

Performance exercise: Division

In the previous post, we discussed the performance space of the minimum function which was implemented via a simple ternary operator and with the help of bit magic. Now we continue to talk about performance and bit hacks. In particular, we will divide a positive number by three:

uint Div3Simple(uint n)   => n / 3;
uint Div3BitHacks(uint n) => (uint)((n * (ulong)0xAAAAAAAB) >> 33);

As usual, it's hard to say which method is faster in advanced because the performance depends on the environment. Here are some interesting results:

Simple BitHacks
LegacyJIT-x86 ≈8.3ns ≈2.6ns
LegacyJIT-x64 ≈2.6ns ≈1.7ns
RyuJIT-x64 ≈6.9ns ≈1.5ns
Mono4.6.2-x86 ≈8.5ns ≈14.4ns
Mono4.6.2-x64 ≈8.3ns ≈2.8ns

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Performance exercise: Minimum

Performance is tricky. Especially, if you are working with very fast operations. In today benchmarking exercise, we will try to measure performance of two simple methods which calculate minimum of two numbers. Sounds easy? Ok, let's do it, here are our guinea pigs for today:

int MinTernary(int x, int y)  => x < y ? x : y;
int MinBitHacks(int x, int y) => x & ((x - y) >> 31) | y & (~(x - y) >> 31);

And here are some results:

Random Const
Ternary BitHacks Ternary BitHacks
LegacyJIT-x86 ≈643µs ≈227µs ≈160µs ≈226µs
LegacyJIT-x64 ≈450µs ≈123µs ≈68µs ≈123µs
RyuJIT-x64 ≈594µs ≈241µs ≈180µs ≈241µs
Mono-x64 ≈203µs ≈283µs ≈204µs ≈282µs

What's going on here? Let's discuss it in detail.

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