The author reverse-engineers the Intel 8087's FPTAN (tangent) instruction by examining its die-level circuitry and microcode. The algorithm combines CORDIC iteration with polynomial approximation to achieve both high accuracy and performance, computing tangent in 90 microseconds versus 13,000 on the 8086.
Background
The Intel 8087, introduced in 1980, was the first x87 floating-point coprocessor and a critical component in early IBM PC systems. Ken Shirriff's popular blog series has reverse-engineered numerous aspects of this chip through die photos and microcode analysis.
- Source
- Lobsters
- Published
- Sep 27, 2026 at 03:01 AM
- Score
- 6.0 / 10