From b0afb8fe0ff1d87165af9df61501197a06240dda Mon Sep 17 00:00:00 2001
From: Lorenz Kästle <12514511+RincewindsHat@users.noreply.github.com>
Date: Sun, 28 Dec 2025 12:13:40 +0100
Subject: Sync with Gnulib stable-202507 code (a8ac9f9ce5)

---
 gl/m4/byteswap.m4 | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

(limited to 'gl/m4/byteswap.m4')

diff --git a/gl/m4/byteswap.m4 b/gl/m4/byteswap.m4
index 0c76fe93..b53cb4d0 100644
--- a/gl/m4/byteswap.m4
+++ b/gl/m4/byteswap.m4
@@ -1,18 +1,42 @@
 # byteswap.m4
-# serial 5
-dnl Copyright (C) 2005, 2007, 2009-2024 Free Software Foundation, Inc.
+# serial 7
+dnl Copyright (C) 2005, 2007, 2009-2025 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.
 
 dnl Written by Oskar Liljeblad.
 
 AC_DEFUN([gl_BYTESWAP],
 [
   dnl Prerequisites of lib/byteswap.in.h.
-  AC_CHECK_HEADERS([byteswap.h], [
+  AC_CHECK_HEADERS_ONCE([byteswap.h])
+  if test $ac_cv_header_byteswap_h = yes; then
+    AC_CACHE_CHECK([for working bswap_16, bswap_32, bswap_64],
+      [gl_cv_header_working_byteswap_h],
+      [gl_cv_header_working_byteswap_h=no
+       dnl Check that floating point arguments work.
+       dnl This also checks C libraries with implementations like
+       dnl '#define bswap_16(x) (((x) >> 8 & 0xff) | (((x) & 0xff) << 8))'
+       dnl that mistakenly evaluate their arguments multiple times.
+       AC_COMPILE_IFELSE(
+         [AC_LANG_PROGRAM(
+            [[#include <byteswap.h>
+            ]],
+            [[int value_16 = bswap_16 (0.0);
+              int value_32 = bswap_32 (0.0);
+              int value_64 = bswap_64 (0.0);
+              return !(value_16 + value_32 + value_64);
+            ]])
+         ],
+         [gl_cv_header_working_byteswap_h=yes],
+         [gl_cv_header_working_byteswap_h=no])
+      ])
+  fi
+  if test "$gl_cv_header_working_byteswap_h" = yes; then
     GL_GENERATE_BYTESWAP_H=false
-  ], [
+  else
     GL_GENERATE_BYTESWAP_H=true
-  ])
+  fi
 ])
-- 
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