Add patch to disable some troublesome FPU tests on i386

Some Abseil tests test floating-point edge cases. These tests are
correct when IEEE semantics are strictly enforced. However, such
semantics are quite expensive when using an x87 FPU, so they’re not
enabled by default. Patch out the offending tests on i386 systems that
don’t enforce IEEE semantics.

2 files changed, 142 insertions, 0 deletions

diff --git a/debian/patches/float-tests-disable-i386.diff b/debian/patches/float-tests-disable-i386.diff
new file mode 100644
index 00000000..0aef2805
--- /dev/null
+++ b/debian/patches/float-tests-disable-i386.diff
@@ -0,0 +1,141 @@
+From: Benjamin Barenblat <bbaren@google.com>
+Subject: Skip floating-point edge-case tests when using an x87
+Forwarded: yes
+Applied-Upstream: https://github.com/abseil/abseil-cpp/commit/311bbd2e50ea35e921a08186840d3b6ca279e880
+
+32-bit Intel CPUs use 80-bit floats for intermediate values, which can
+change the results of floating point computations from what we normally
+expect. Identify tests that are sensitive to the x87, and skip them when
+we’re on 32-bit Intel.
+
+The author works at Google. Upstream applied this patch as Piper
+revision 378722613 and exported it to GitHub; the Applied-Upstream URL
+above points to the exported commit.
+
+--- a/absl/random/beta_distribution_test.cc
++++ b/absl/random/beta_distribution_test.cc
+@@ -15,6 +15,7 @@
+ #include "absl/random/beta_distribution.h"
+ 
+ #include <algorithm>
++#include <cfloat>
+ #include <cstddef>
+ #include <cstdint>
+ #include <iterator>
+@@ -558,6 +559,14 @@
+ // dependencies of the distribution change, such as RandU64ToDouble, then this
+ // is also likely to change.
+ TEST(BetaDistributionTest, AlgorithmBounds) {
++#if (defined(__i386__) || defined(_M_IX86)) && FLT_EVAL_METHOD != 0
++  // We're using an x87-compatible FPU, and intermediate operations are
++  // performed with 80-bit floats. This produces slightly different results from
++  // what we expect below.
++  GTEST_SKIP()
++      << "Skipping the test because we detected x87 floating-point semantics";
++#endif
++
+   {
+     absl::random_internal::sequence_urbg urbg(
+         {0x7fbe76c8b4395800ull, 0x8000000000000000ull});
+--- a/absl/random/distributions_test.cc
++++ b/absl/random/distributions_test.cc
+@@ -14,6 +14,7 @@
+ 
+ #include "absl/random/distributions.h"
+ 
++#include <cfloat>
+ #include <cmath>
+ #include <cstdint>
+ #include <random>
+@@ -224,6 +225,15 @@
+ TEST_F(RandomDistributionsTest, UniformNonsenseRanges) {
+   // The ranges used in this test are undefined behavior.
+   // The results are arbitrary and subject to future changes.
++
++#if (defined(__i386__) || defined(_M_IX86)) && FLT_EVAL_METHOD != 0
++  // We're using an x87-compatible FPU, and intermediate operations can be
++  // performed with 80-bit floats. This produces slightly different results from
++  // what we expect below.
++  GTEST_SKIP()
++      << "Skipping the test because we detected x87 floating-point semantics";
++#endif
++
+   absl::InsecureBitGen gen;
+ 
+   // <uint>
+--- a/absl/random/exponential_distribution_test.cc
++++ b/absl/random/exponential_distribution_test.cc
+@@ -15,6 +15,7 @@
+ #include "absl/random/exponential_distribution.h"
+ 
+ #include <algorithm>
++#include <cfloat>
+ #include <cmath>
+ #include <cstddef>
+ #include <cstdint>
+@@ -384,6 +385,15 @@
+ TEST(ExponentialDistributionTest, AlgorithmBounds) {
+   // Relies on absl::uniform_real_distribution, so some of these comments
+   // reference that.
++
++#if (defined(__i386__) || defined(_M_IX86)) && FLT_EVAL_METHOD != 0
++  // We're using an x87-compatible FPU, and intermediate operations can be
++  // performed with 80-bit floats. This produces slightly different results from
++  // what we expect below.
++  GTEST_SKIP()
++      << "Skipping the test because we detected x87 floating-point semantics";
++#endif
++
+   absl::exponential_distribution<double> dist;
+ 
+   {
+--- a/absl/random/uniform_real_distribution_test.cc
++++ b/absl/random/uniform_real_distribution_test.cc
+@@ -14,6 +14,7 @@
+ 
+ #include "absl/random/uniform_real_distribution.h"
+ 
++#include <cfloat>
+ #include <cmath>
+ #include <cstdint>
+ #include <iterator>
+@@ -70,6 +71,14 @@
+ TYPED_TEST_SUITE(UniformRealDistributionTest, RealTypes);
+ 
+ TYPED_TEST(UniformRealDistributionTest, ParamSerializeTest) {
++#if (defined(__i386__) || defined(_M_IX86)) && FLT_EVAL_METHOD != 0
++  // We're using an x87-compatible FPU, and intermediate operations are
++  // performed with 80-bit floats. This produces slightly different results from
++  // what we expect below.
++  GTEST_SKIP()
++      << "Skipping the test because we detected x87 floating-point semantics";
++#endif
++
+   using param_type =
+       typename absl::uniform_real_distribution<TypeParam>::param_type;
+ 
+--- a/absl/time/duration_test.cc
++++ b/absl/time/duration_test.cc
+@@ -17,6 +17,7 @@
+ #endif
+ 
+ #include <chrono>  // NOLINT(build/c++11)
++#include <cfloat>
+ #include <cmath>
+ #include <cstdint>
+ #include <ctime>
+@@ -1390,6 +1391,14 @@
+ // Seconds(point) returns a duration near point * Seconds(1.0). (They may
+ // not be exactly equal due to fused multiply/add contraction.)
+ TEST(Duration, ToDoubleSecondsCheckEdgeCases) {
++#if (defined(__i386__) || defined(_M_IX86)) && FLT_EVAL_METHOD != 0
++  // We're using an x87-compatible FPU, and intermediate operations can be
++  // performed with 80-bit floats. This means the edge cases are different than
++  // what we expect here, so just skip this test.
++  GTEST_SKIP()
++      << "Skipping the test because we detected x87 floating-point semantics";
++#endif
++
+   constexpr uint32_t kTicksPerSecond = absl::time_internal::kTicksPerSecond;
+   constexpr auto duration_tick = absl::time_internal::MakeDuration(0, 1u);
+   int misses = 0;
diff --git a/debian/patches/series b/debian/patches/series
index 4e55e401..3f1a11da 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -4,3 +4,4 @@ latomic.diff
 cordrepring-typo.diff
 thumb-function-bounds.diff
 float-rounding.diff
+float-tests-disable-i386.diff