477: One Thousand New Instructions
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SIMD on a Cortex-M4 Processor
A significant performance improvement of 16x was achieved by avoiding re-initializing the histogram for every pixel, transitioning from O(N^2) to O(2N) complexity. This optimization is crucial for MCUs, where even small changes make a massive difference. By leveraging SIMD on a Cortex-M4 processor, it is possible to compute multiple columns of the histogram simultaneously, by utilizing a specific instruction that operates on four bytes at a time. This capability has been available in Cortex-M4 processors for over a decade, enabling parallel additions and preventing overflow, thereby enhancing computational efficiency.
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