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by CalChris 1103 days ago
To be fair, RISC-V has a small base, RV64I in the 64-bit case. These bases are small, reduced and frozen. But after that, yes, the extensions get whacky. L is Decimal Floating Point, still marked Open. I'm not sure what's reduced about that. But extensions are optional.

About the history of RISC, the basic idea dates to Seymour Cray's 1964 CDC 6600. I don't think Berkeley gives Cray enough credit.
2 comments
dvwobuq 1103 days ago
Patterson and Waterman detail exactly what they we’re thinking during the design of RISCV in the RISCV Reader and Cray is mentioned in multiple places.

https://www.goodreads.com/en/book/show/36604301

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CalChris 1103 days ago
Cray gets mentioned in the Reader 3 times, the simplicity quote, the pioneer quote and the timeline comparison with the Iliac-4 (p. 80). Waterman's thesis does actually give some credit:

  The CDC 6600 [95] and Cray-1 [82] ISAs, in many respects the precursors to RISC, each had two lengths of instruction, albeit without the redundancy property of the Stretch.
https://www2.eecs.berkeley.edu/Pubs/TechRpts/2016/EECS-2016-...
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hajile 1103 days ago
IEEE 754 specifies not only floating point, but decimal floating point too. You actually find hardware implementations on some systems (notably IBM POWER).

Better to reserve and not finish that to be unprepared.

In any case, decimal floating point is better for MOST programs/programmers and is only inferior in being harder to implement (imo).

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