I merged this now, thank you! I added another patch (attached) to make the decision to use the slice-by-8 implementation a maintainer option rather than something visible to end-users. That also fixes the ./configure stdout output, you forgot the corresponding AC_MSG_RESULT to the AC_MSG_CHECKING. I don't think it makes sense for normal users to be exposed to this fairly internal implementation choice. The slice-by-8 implementation is now the default, and maintainers who wish to disable it for projects that are really low on memory can add gl_DISABLE_CRC_SLICE_BY_8 early on in configure.ac. Advanced users can disable it with `gl_crc_slice_by_8=no ./configure' too. I expect this to be exceptionally rare, although I do have a use-case for this myself so I appreciate this being configurable.
Can you build gzip with an updated gnulib and compare speed? And run the self-test suite too, to add some assurance we didn't mess up anything. A next step would be to evaluate if the assembler CRC instructions help further on some platforms... /Simon
From cc3fb685ac370a368cb84480117be13d109eebf0 Mon Sep 17 00:00:00 2001
From: Simon Josefsson <si...@josefsson.org>
Date: Thu, 31 Oct 2024 13:10:34 +0100
Subject: [PATCH] crc: make it a maintainer setting rather than a user setting.
* m4/crc.m4 (gl_CRC_SLICE_BY_8): Drop AC_ARG_ENABLE.
---
ChangeLog | 5 +++++
m4/crc.m4 | 23 +++++++++++++----------
2 files changed, 18 insertions(+), 10 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 42367f8135..b0719c23bf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2024-10-31 Simon Josefsson <si...@josefsson.org>
+
+ crc: make it a maintainer setting rather than a user setting.
+ * m4/crc.m4 (gl_CRC_SLICE_BY_8): Drop AC_ARG_ENABLE.
+
2024-10-27 Sam Russell <sam.h.russ...@gmail.com>
crc: New optimised slice-by-8 implementation
diff --git a/m4/crc.m4 b/m4/crc.m4
index 0007b7274e..f62987e78e 100644
--- a/m4/crc.m4
+++ b/m4/crc.m4
@@ -1,22 +1,25 @@
# crc.m4
-# serial 3
-dnl Copyright (C) 2024-2024 Free Software Foundation, Inc.
+# serial 4
+dnl Copyright (C) 2024 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
dnl This file is offered as-is, without any warranty.
+# For use by maintainer's after gl_EARLY in configure.ac.
+AC_DEFUN([gl_DISABLE_CRC_SLICE_BY_8],
+[
+ gl_crc_slice_by_8=no
+])
+
AC_DEFUN([gl_CRC_SLICE_BY_8],
[
AC_MSG_CHECKING([whether to enable CRC slice-by-8 algorithm])
- AC_ARG_ENABLE([crc-slice-by-8],
- [AS_HELP_STRING([[--disable-crc-slice-by-8]],
- [disable CRC slice-by-8 algorithm])],
- [enable_crc_slice_by_8=$enableval],
- [enable_crc_slice_by_8=yes])
-
- if test $enable_crc_slice_by_8 = yes; then
+ if test x"$gl_crc_slice_by_8" != x"no"; then
+ AC_MSG_RESULT([yes])
AC_DEFINE([GL_CRC_SLICE_BY_8], [1],
- [Define to get faster but larger CRC32 operation.])
+ [Define to get faster but larger CRC32 operation.])
+ else
+ AC_MSG_RESULT([no])
fi
])
--
2.46.0
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