Public review for standard extensions Zc including Zca, Zcf, Zcd, Zcb, Zcmp, Zcmt

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Tariq Kurd

Oct 12, 2022, 11:21:33 AM10/12/22

We are delighted to announce the start of the public review period for the following proposed standard extensions to the RISC-V ISA:

Zca - instructions in the C extension that do not include the floating-point loads and stores.
Zcf - the existing set of compressed single precision floating point loads and stores: c.flw, c.flwsp, c.fsw, c.fswsp.
Zcd - existing set of compressed double precision floating point loads and stores: c.fld, c.fldsp, c.fsd, c.fsdsp.
Zcb - simple code-size saving instructions which are easy to implement on all CPUs
Zcmp - a set of instructions which may be executed as a series of existing 32-bit RISC-V instructions (push/pop and double move)
Zcmt - adds the table jump instructions and also adds the JVT CSR

The review period begins today, 12th October 2022 and ends on 26th November 2022 (inclusive).

This extension is part of the Unprivileged Specification.

These extensions are described in the PDF spec available at:

which was generated from the source available in the following GitHub repo:

To respond to the public review, please either email comments to the public isa-dev mailing list or add issues and/or pull requests (PRs) to the code-size-reduction GitHub repo: . We welcome all input and appreciate your time and effort in helping us by reviewing the specification.

During the public review period, corrections, comments, and suggestions, will be gathered for review by the Code-Size Reduction Task Group. Any minor corrections and/or uncontroversial changes will be incorporated into the specification. Any remaining issues or proposed changes will be addressed in the public review summary report. If there are no issues that require incompatible changes to the public review specification, the Unprivileged ISA Committee will recommend the updated specifications be approved and ratified by the RISC-V Technical Steering Committee and the RISC-V Board of Directors.

Thanks to all the contributors for all their hard work.

Tariq Kurd

Chair, Code-size reduction


Tariq Kurd | Lead IP Architect | Codasip UK Design Centre |

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