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Reverse-engineering Intel 8087's tangent algorithm reveals integration of CORDIC and polynomial approximations

The article explores the tangent instruction algorithm of the Intel 8087 floating-point chip.

WHY IT MATTERS

Understanding the 8087's tangent algorithm enhances knowledge of historical computing techniques. It showcases the integration of different mathematical approaches, which can inform modern algorithm design. Examining such vintage technology can inspire innovative solutions in contemporary engineering applications.

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The three things worth knowing

01

The Intel 8087 introduced in 1980 significantly accelerated floating-point operations compared to the 8086 microprocessor.

02

The algorithm for the tangent instruction combines CORDIC with polynomial approximation for improved accuracy and performance.

03

Reverse-engineering techniques utilized included physical examination of the chip's circuitry and high-resolution imaging.

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ORIGINAL ANALYSIS

The Intel 8087, introduced in 1980, greatly improved the speed of floating-point calculations, particularly for tangent operations, which now took only 90 microseconds compared to 13,000 microseconds with its predecessor. This advancement represented a substantial leap in computing power for applications requiring rapid mathematical calculations.

The tangent instruction algorithm of the 8087 is notable for its hybrid approach, integrating CORDIC, which relies on shift and add methods, with polynomial approximations. This combination allowed for both high performance and accuracy, suggesting a sophisticated understanding of computational needs and hardware limitations at the time of design.

The reverse-engineering process involved examining the microcode and circuitry of the 8087, revealing the complexity of the chip's design. This level of detailed investigation not only sheds light on historical computing methods but may also provide insights into optimizing current and future algorithms based on similar principles.

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THE CLUSTER

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Ken Shirriff's blog Reverse-engineering the vintage Intel 8087's tangent algorithm: more than CORDIC Open ↗
Ken Shirriff's blog via Lobsters Reverse-engineering the vintage Intel 8087's tangent algorithm: more than CORDIC Open ↗