[PATCH v4 6/6] qht: Fix threshold rate calculation

[Richard Henderson <richard.henderson@linaro.org>]

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;
                          ~ ^~~~~~~~~~

Fix this by splitting the 64-bit constant into two halves,
each of which is individually perfectly representable, the
sum of which produces the correct arithmetic result.

Cc: Emilio G. Cota <cota@braap.org>
Reported-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
Question: Should we really be scaling by UINT64_MAX?

The comparisons against info->r mean that 1.0 is exceedingly unlikely
to hit.  Or if that is supposed to be the point, why is is the test

  r >= threshold
not
  r > threshold

where, if threshold == UINT64_MAX, there is zero chance of the
test being true for 1.0.
---
 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..eb88a90137 100644
--- a/tests/qht-bench.c
+++ b/tests/qht-bench.c
@@ -284,7 +284,8 @@ static void do_threshold(double rate, uint64_t *threshold)
     if (rate == 1.0) {
         *threshold = UINT64_MAX;
     } else {
-        *threshold = rate * UINT64_MAX;
+        *threshold = (rate * 0xffff000000000000ull)
+                   + (rate * 0x0000ffffffffffffull);
     }
 }
 
-- 
2.25.1