Re: [PATCH v2] tests/qht-bench: Fix Clang 'int-conversion' warning

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Wrong subject =) v3 coming...

On 5/4/20 4:41 PM, Philippe Mathieu-Daudé wrote:
> When building with Clang 10 on Fedora 32, we get:
> 
>    tests/qht-bench.c:287:29: error: implicit conversion from 'unsigned long' to 'double' changes value from 18446744073709551615 to 18446744073709551616 [-Werror,-Wimplicit-int-float-conversion]
>            *threshold = rate * UINT64_MAX;
>                              ~ ^~~~~~~~~~
>    /usr/include/stdint.h:130:23: note: expanded from macro 'UINT64_MAX'
>    # define UINT64_MAX             (__UINT64_C(18446744073709551615))
>                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    /usr/include/stdint.h:107:25: note: expanded from macro '__UINT64_C'
>    #  define __UINT64_C(c) c ## UL
>                            ^~~~~~~
>    <scratch space>:14:1: note: expanded from here
>    18446744073709551615UL
>    ^~~~~~~~~~~~~~~~~~~~~~
> 
> Fix by using nextafter() from <math.h>:
> 
>    double nextafter( double from, double to );
> 
>        Returns the next representable value of 'from'
>        in the direction of 'to'.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> Since v1: nextafterf() -> nextafter()
> 
> Cc: Emilio G. Cota <cota@braap.org>
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Alexander Bulekov <alxndr@bu.edu>
> ---
>   tests/qht-bench.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/qht-bench.c b/tests/qht-bench.c
> index e3b512f26f..54ce1e8188 100644
> --- a/tests/qht-bench.c
> +++ b/tests/qht-bench.c
> @@ -10,6 +10,7 @@
>   #include "qemu/qht.h"
>   #include "qemu/rcu.h"
>   #include "qemu/xxhash.h"
> +#include <math.h>
>   
>   struct thread_stats {
>       size_t rd;
> @@ -284,7 +285,7 @@ static void do_threshold(double rate, uint64_t *threshold)
>       if (rate == 1.0) {
>           *threshold = UINT64_MAX;
>       } else {
> -        *threshold = rate * UINT64_MAX;
> +        *threshold = rate * nextafter(0x1p64, 0.0);
>       }
>   }
>   
>