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Why Did Intel Use the Wrong Pi?
James Gosling says Intel used an incorrect version of pi for sine and cosine because of an early launch and restrictions on what silicon could do at the time.
Sine and cosine repeat, so only the span from negative pi to positive pi makes a difference once an angle is larger. Range reduction folds the angle back in by taking the angle modulo 2 pi, and Intel's pi for that step was slightly wrong. In the numerical analysis community, a rotating shaft in a motor or a propeller on an airplane turns RPM times time into an angle, and the result is the sine and cosine of a very large angle.
The mistake looks like a minor nit. The day starts with issues people have moving software across wildly different proprietary platforms, and the work turns into a deep dive on how sine and cosine are evaluated.
