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Add a "template" crc-clmul-template.h that can generate RISC-V Zbc optimized CRC functions. Each generated CRC function is parameterized by CRC length and bit order, and it accepts a pointer to the constants struct required for the specific CRC polynomial desired. Update gen-crc-consts.py to support generating the needed constants structs. This makes it possible to easily wire up a Zbc optimized implementation of almost any CRC. The design generally follows what I did for x86, but it is simplified by using RISC-V's scalar carryless multiplication Zbc, which has no equivalent on x86. RISC-V's clmulr instruction is also helpful. A potential switch to Zvbc (or support for Zvbc alongside Zbc) is left for future work. For long messages Zvbc should be fastest, but it would need to be shown to be worthwhile over just using Zbc which is significantly more convenient to use, especially in the kernel context. Compared to the existing Zbc-optimized CRC32 code and the earlier proposed Zbc-optimized CRC-T10DIF code (https://lore.kernel.org/r/20250211071101.181652-1-zhihang.shao.iscas@gmail.com), this submission deduplicates the code among CRC variants and is significantly more optimized. It uses "folding" to take better advantage of instruction-level parallelism (to a more limited extent than x86 for now, but it could be extended to more), it reworks the Barrett reduction to eliminate unnecessary instructions, and it documents all the math used and makes all the constants reproducible. Tested-by: Björn Töpel <bjorn@rivosinc.com> Acked-by: Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20250216225530.306980-2-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.