Branchless Programming: Difference between revisions
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This is one way to simulate switch statements. | This is one way to simulate switch statements. | ||
Technically these do not have branching but will have a memory read which could be just as slow as a single branch. | Technically these do not have branching but will have a memory read which could be just as slow as a single branch. | ||
< | <syntaxhighlight lang="python"> | ||
# Cache the following at the start of your program or in the constructor | # Cache the following at the start of your program or in the constructor | ||
# Assume we have some functions batch_norm(), group_norm() | # Assume we have some functions batch_norm(), group_norm() | ||
| Line 41: | Line 41: | ||
# At runtime, you can do: | # At runtime, you can do: | ||
x = my_cache[operation](x) | x = my_cache[operation](x) | ||
</ | </syntaxhighlight> | ||
==Booleans== | |||
Multiplications by booleans can be used instead of switch statements. | |||
Rather than doing | Rather than doing | ||
< | <syntaxhighlight lang="cpp"> | ||
if age > 10 | if (age > 10) { | ||
x = | x += 10; | ||
else | } else { | ||
x = | x -= 10; | ||
</ | } | ||
</syntaxhighlight> | |||
you can do | you can do | ||
< | <syntaxhighlight lang="cpp"> | ||
x = x + (20 * (age > 10) - 10); | |||
// or | // or | ||
y = age > 10 | y = age > 10; | ||
x = x + 10 * y - 10 * | x = x + 10 * y - 10 * !y; | ||
</ | </syntaxhighlight> | ||
These are micro optimizations but they | Similarly, instead of doing | ||
<syntaxhighlight lang="cpp"> | |||
if (age > 10) { | |||
x++; | |||
} | |||
</syntaxhighlight> | |||
you can just write <code>x += age>10;</code>. | |||
These are micro optimizations but they could be useful for speeding up GPU shaders in some cases. | |||
In high-level programming languages such as Python, these tricks can actually slow down your code<ref name="branchless-slower-python">https://stackoverflow.com/questions/72118249/why-are-the-branchless-and-built-in-functions-slower-in-python</ref>. | |||
==Resources== | ==Resources== | ||
* [https://francescocirillo.com/pages/anti-if-campaign Anti If Campaign] | * [https://francescocirillo.com/pages/anti-if-campaign Anti If Campaign] | ||
* [https://code.joejag.com/2016/anti-if-the-missing-patterns.html Anti-If: The missing patterns] | |||
==References== | |||
<references /> | |||