From 6dbbada2b05bdc5efd0a5592a7805c92fe0531c6 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 20 May 2024 09:08:27 -0700
Subject: [PATCH] * m4/byteswap.m4: Add comment about broken C libraries.

---
 m4/byteswap.m4 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/m4/byteswap.m4 b/m4/byteswap.m4
index 3f5ef45cfe..3185bab763 100644
--- a/m4/byteswap.m4
+++ b/m4/byteswap.m4
@@ -15,6 +15,10 @@ AC_DEFUN([gl_BYTESWAP],
     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>
-- 
2.40.1