fenv-exceptions-trapping tests: Comments

[Bruno Haible]

A small riddle: What does this loop do?

  int exceptions = 0;
  do
    {
      ...
      exceptions = (exceptions - FE_ALL_EXCEPT) & FE_ALL_EXCEPT;
    }
  while (exceptions != 0);



2023-11-07  Bruno Haible  <bruno@clisp.org>

        fenv-exceptions-trapping tests: Comments.
        * tests/test-fenv-except-trapping-1.c (main): Add a comment.

diff --git a/tests/test-fenv-except-trapping-1.c 
b/tests/test-fenv-except-trapping-1.c
index 7c67a06ec9..e717bb1739 100644
--- a/tests/test-fenv-except-trapping-1.c
+++ b/tests/test-fenv-except-trapping-1.c
@@ -44,7 +44,11 @@ main ()
   unsigned int a, b;
 
   /* Run through all possible valid arguments to feenableexcept and
-     fedisableexcept.  */
+     fedisableexcept.
+     An alternative way of coding this iteration, without the 
uint_to_exceptions
+     function, would be using the trick from
+     Jörg Arndt: Matters Computational <https://www.jjj.de/fxt/fxtbook.pdf>
+     § 1.25.1 Generating bit subsets of a given word  */
   for (a = 0; a < 0x20; a++)
     for (b = 0; b < 0x20; b++)
       {