Round a double multiplication before casting it to integer

Forwarded: yes
Applied-Upstream: https://github.com/abseil/abseil-cpp/commit/60be12ed9822078970f05f3c560324184302df6b

The code

    static_cast<int>(x * y)

(for double x and y) performs a double multiplication into a temporary
that, by standard, may have excess precision. The subsequent cast to int
discards the excess precision. However, the cast may examine the excess
precision during conversion, producing surprising results like

    static_cast<int>(1.7 * 10) == 16

on certain systems. Correct this case by explicitly rounding 1.7 * 10
before casting it.

The author works at Google. Upstream applied this patch as Piper
revision 378922064 and exported it to GitHub; the Applied-Upstream URL
above points to the exported commit.

Gbp-Pq: Name missing-rint.diff

diff --git a/absl/random/mocking_bit_gen_test.cc b/absl/random/mocking_bit_gen_test.cc
index f63b6e420e0c299a0a621e46a5da233489f062f9..c713ceafd26e2d785c73dac4a7e9de2ee63caec4 100644 (file)
--- a/absl/random/mocking_bit_gen_test.cc
+++ b/absl/random/mocking_bit_gen_test.cc
@@ -15,6 +15,7 @@
 //
 #include "absl/random/mocking_bit_gen.h"
 
+#include <cmath>
 #include <numeric>
 #include <random>
 
@@ -328,8 +329,9 @@ TEST(BasicMocking, WillByDefaultWithArgs) {
 
   absl::MockingBitGen gen;
   ON_CALL(absl::MockPoisson<int>(), Call(gen, _))
-      .WillByDefault(
-          [](double lambda) { return static_cast<int>(lambda * 10); });
+      .WillByDefault([](double lambda) {
+        return static_cast<int>(std::rint(lambda * 10));
+      });
   EXPECT_EQ(absl::Poisson<int>(gen, 1.7), 17);
   EXPECT_EQ(absl::Poisson<int>(gen, 0.03), 0);
 }