Quadrupling code performance with a "useless" if
A software developer explains how adding a seemingly redundant 'if' statement significantly improved the performance of a domain-specific compression algorithm. The optimization relates to how the CPU handles branch prediction and instruction flow during a specific loop.
Why it matters
It demonstrates the counter-intuitive nature of low-level performance optimization and the importance of understanding hardware-level execution.
Quadrupling code performance with a "useless" if | purplesyringa's blog
Quadrupling code performance with a "useless" if July 12, 2026 So I was optimizing a domain-specific compressor the other day , as one does. One important problem was chunking the input string and optimally choosing the most compact encoding for each chunk (different encodings compress different characters better, so where to split is not immediately obvious). The previous post describes the algorithm if you’re interested, but it boils down to finding the shortest path on a grid. For each cell, the algorithm computes the best cell following it. Following references from the first cell to the last one gives the optimal coding order.
uint8_t next_j[n_symbols][ 8 ]; // references to the next cell
// The core of the algorithm populating `next_j`.
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