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Booth's algorithm follows this old scheme by performing an addition when it encounters the first digit of a block of ones (0 1) and subtraction when it encounters the end of the block (1 0). This works for a negative multiplier as well. When the ones in a multiplier are grouped into long blocks, Booth's algorithm performs fewer additions and subtractions than the normal multiplication algorithm.
== Pentium multiplier implementation ==
Intel's [[Pentium]] microprocessor uses a radix-8 variant of Booth's algorithm in its 64-bit hardware multiplier. Because of the way it implements the radix-8 multiplication, it needs a complex auxiliary circuit to perform the special case of multiplication by 3 in a way that minimizes latency, combining the use of [[Carry-lookahead adder|carry-lookahead]], [[carry-select addition|carry-select]], and [[Kogge–Stone addition]].<ref>{{Cite web |first=Ken|last=Shirriff|title=The Pentium contains a complicated circuit to multiply by three |url=https://www.righto.com/2025/03/pentium-multiplier-adder-reverse-engineered.html |access-date=2025-03-03|website=righto.com}}</ref>
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