[PATCH 0/3] newlib: riscv: Add and optimize memchr() and memrchr() functions

[Eric Salem]

The RISC-V port currently does not have its own implementations of
memchr() and memrchr(). Instead it uses the stock version that's common
to any port that omits its own implementations.

This patch series adds port-specific implementations of both. It
improves upon the algorithm that's currently used, and also uses RISC-V
extensions when available.

The proposed implementations were benchmarked on a Raspberry Pi Pico 2.
A 2 KB buffer was was used, and an offset into the buffer ranging from
0-2047 was set where the matching byte would be found.

To ensure that the benchmarking is objective as possible, a range of
addresses with various alignments were tested so neither algorithm had
an advantage. Addresses divided by eight with a remainder of 0-7 were
used for the benchmark. For example:

0x20002a80
0x20003289
0x20003a92
0x2000429b
0x20004aa4
0x200052b5
0x20005ac6
0x200062d7

In all cases except two, the proposed memchr() was faster than the
existing. For those two cases they were tied, and both had an offset of
zero and unaligned addresses for the buffer. A total of 16,384 cases
were tested.

The existing memrchr() implementation currently does misaligned
accesses, and so could not be benchmarked properly on the Pico 2. But
considering that every word load is misaligned, the proposed
implementation will be faster since it does aligned accesses only. The
algorithm was also improved upon in the same fashion as memchr(), along
with using RISC-V extensions when available.

The final commit in this series is for regenerating a configuration
file. As described elsewhere,[1][2] this file doesn't need to be part
of the series. It's included only to aid in testing the changes without
having to manually regenerate the file.

[1] https://sourceware.org/newlib/faq.html#q8
[2] https://sourceware.org/pipermail/newlib/2025/021500.html

Eric Salem (3):
  newlib: riscv: Add memchr() and memrchr() implementations
  newlib: riscv: Optimize memchr() and memrchr()
  newlib: Regenerate configuration file

 newlib/Makefile.in                     |  41 +++++-
 newlib/libc/machine/riscv/Makefile.inc |   2 +-
 newlib/libc/machine/riscv/memchr.c     | 158 ++++++++++++++++++++++
 newlib/libc/machine/riscv/memrchr.c    | 179 +++++++++++++++++++++++++
 newlib/libc/machine/riscv/rv_string.h  |  45 ++++++-
 newlib/libc/machine/riscv/xlenint.h    |   7 +
 6 files changed, 423 insertions(+), 9 deletions(-)
 create mode 100644 newlib/libc/machine/riscv/memchr.c
 create mode 100644 newlib/libc/machine/riscv/memrchr.c

-- 
2.49.0