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The Intel 8087 combined CORDIC and polynomial approximation for tangent

righto.com 33 min read Editor score 8/10

Reverse-engineering the 8087’s circuitry and microcode reveals a tangent algorithm combining CORDIC with polynomial approximation; it computed tangent in 90 microseconds versus 13,000 on the 8086. The investigation connects implementation details to concrete accuracy and performance trade-offs.

What

The Intel 8087’s FPTAN instruction computes tangent, and its implementation was reverse-engineered from chip circuitry and microcode.

How

The 8087 combines CORDIC with polynomial approximation to achieve high accuracy and performance.

Why it matters

The hybrid design illustrates how hardware can combine algorithms to balance computation speed and accuracy.

Read on righto.com → Lobsters · 2 comments

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