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Reverse-engineering the Intel 8087's tangent algorithm: more than CORDIC

126 points · 11 comments · pwg

  1. cmovq · · focus · HN ↗
    Always thought it was strange that fptan also pushes 1 to the register stack. It now makes sense it’s so existing code for the 8087 which was expected to do y/x to get the actual tangent could keep working by doing y/1 on newer processors.
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