Microcode in Intel's 8087 floating-point chip: the scale instruction

· Ken Shirriff · Sept. 12, 2026, 4:08 p.m.
Summary
This blog post examines the microcode behind the FSCALE instruction of Intel's 8087 floating-point chip, detailing its complexities and the historical context of floating-point arithmetic. Written by Ken Shirriff, it describes the intricacies of the 8087 micro-instructions, challenges of reverse engineering, and the significance of the 8087 in standardizing floating-point operations.
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