Long division is a slow operation in computing, but modern compilers use an efficient alternative when dividing by a constant. Instead of performing the full division, they transform the operation into a combination of multiplication and bit shifting. This optimization relies on mathematical principles involving reciprocals and modular arithmetic to produce correct results while drastically reducing computation time. The transformation is handled automatically, often without any change to the source code.
Matt Godbolt illustrates this process with a simple C program and examines the resulting assembly output. He explains how the compiler selects appropriate constants for the multiplication step based on the divisor. This technique showcases how high-level code can be optimized at the machine level, improving performance transparently. Understanding such tricks helps developers write more efficient code and appreciate the sophisticated work done by compilers behind the scenes.