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authorGravatar Abseil Team <absl-team@google.com>2019-03-12 11:39:15 -0700
committerGravatar vslashg <gfalcon@google.com>2019-03-12 15:07:34 -0400
commit256be563447a315f2a7993ec669460ba475fa86a (patch)
tree80d363bf7055929227415cd3f46f1b1ac62b6944 /absl/numeric
parent88a152ae747c3c42dc9167d46c590929b048d436 (diff)
Export of internal Abseil changes.
-- 00d42e3d5433aaf29c2ed293520b2ba178ae8bdb by Greg Falcon <gfalcon@google.com>: Import of CCTZ from GitHub. PiperOrigin-RevId: 238061818 -- 867a7ca318fac2991ea9a4107dbae3cc9fbf974a by Abseil Team <absl-team@google.com>: Added a IWYU export pragma when including a standard header for the purpose of aliasing its symbols. PiperOrigin-RevId: 238022277 -- 17047745058f2f151cd986ea9f649512542d3876 by Matt Armstrong <marmstrong@google.com>: Clarify the comment discouraging WrapUnique<T>(x) calls. PiperOrigin-RevId: 237873803 -- 3dcb2e4968243d33ca0ce53280c445df50f4a7ec by Samuel Benzaquen <sbenza@google.com>: Workaround clang bug https://bugs.llvm.org/show_bug.cgi?id=38289 PiperOrigin-RevId: 237873551 -- f348d2dc7087a990cbdfb95aa51fd7ff478ae40e by Samuel Benzaquen <sbenza@google.com>: Reduce minimum capacity to 1. This reduces memory usage for small tables. A flat_hash_set<int> of 1 element goes from 92 bytes to 24. A flat_hash_set<string> of 1 element goes from 512 bytes to 56. PiperOrigin-RevId: 237859811 -- 9c8125be5e4e5d22a7bb62bdec8c323338385c1b by Jon Cohen <cohenjon@google.com>: Bump to CMake 3.5. This is the oldest modern cmake being included by default in most popular OS distributions according to https://repology.org/project/cmake/versions. Specifically, Ubuntu LTS 16.04 uses cmake 3.5 (https://packages.ubuntu.com/xenial/cmake) PiperOrigin-RevId: 237859345 -- 07638d672e0a4dced986a62750cfd8318ed36ffa by Derek Mauro <dmauro@google.com>: Import of CCTZ from GitHub. PiperOrigin-RevId: 237714597 GitOrigin-RevId: 00d42e3d5433aaf29c2ed293520b2ba178ae8bdb Change-Id: I5faecc45add4a5a774d4f9baf06e5519091f2ccc
Diffstat (limited to 'absl/numeric')
-rw-r--r--absl/numeric/int128.cc22
-rw-r--r--absl/numeric/int128_test.cc14
2 files changed, 36 insertions, 0 deletions
diff --git a/absl/numeric/int128.cc b/absl/numeric/int128.cc
index 33f528ce..93b62c52 100644
--- a/absl/numeric/int128.cc
+++ b/absl/numeric/int128.cc
@@ -123,6 +123,28 @@ uint128 MakeUint128FromFloat(T v) {
return MakeUint128(0, static_cast<uint64_t>(v));
}
+
+#if defined(__clang__) && !defined(__SSE3__)
+// Workaround for clang bug: https://bugs.llvm.org/show_bug.cgi?id=38289
+// Casting from long double to uint64_t is miscompiled and drops bits.
+// It is more work, so only use when we need the workaround.
+uint128 MakeUint128FromFloat(long double v) {
+ // Go 50 bits at a time, that fits in a double
+ static_assert(std::numeric_limits<double>::digits >= 50, "");
+ static_assert(std::numeric_limits<long double>::digits <= 150, "");
+ // Undefined behavior if v is not finite or cannot fit into uint128.
+ assert(std::isfinite(v) && v > -1 && v < std::ldexp(1.0L, 128));
+
+ v = std::ldexp(v, -100);
+ uint64_t w0 = static_cast<uint64_t>(static_cast<double>(std::trunc(v)));
+ v = std::ldexp(v - static_cast<double>(w0), 50);
+ uint64_t w1 = static_cast<uint64_t>(static_cast<double>(std::trunc(v)));
+ v = std::ldexp(v - static_cast<double>(w1), 50);
+ uint64_t w2 = static_cast<uint64_t>(static_cast<double>(std::trunc(v)));
+ return (static_cast<uint128>(w0) << 100) | (static_cast<uint128>(w1) << 50) |
+ static_cast<uint128>(w2);
+}
+#endif // __clang__ && !__SSE3__
} // namespace
uint128::uint128(float v) : uint128(MakeUint128FromFloat(v)) {}
diff --git a/absl/numeric/int128_test.cc b/absl/numeric/int128_test.cc
index 216ec50c..5e1b5ec3 100644
--- a/absl/numeric/int128_test.cc
+++ b/absl/numeric/int128_test.cc
@@ -271,6 +271,20 @@ TEST(Uint128, ConversionTests) {
EXPECT_EQ(static_cast<absl::uint128>(round_to_zero), 0);
EXPECT_EQ(static_cast<absl::uint128>(round_to_five), 5);
EXPECT_EQ(static_cast<absl::uint128>(round_to_nine), 9);
+
+ absl::uint128 highest_precision_in_long_double =
+ ~absl::uint128{} >> (128 - std::numeric_limits<long double>::digits);
+ EXPECT_EQ(highest_precision_in_long_double,
+ static_cast<absl::uint128>(
+ static_cast<long double>(highest_precision_in_long_double)));
+ // Apply a mask just to make sure all the bits are the right place.
+ const absl::uint128 arbitrary_mask =
+ absl::MakeUint128(0xa29f622677ded751, 0xf8ca66add076f468);
+ EXPECT_EQ(highest_precision_in_long_double & arbitrary_mask,
+ static_cast<absl::uint128>(static_cast<long double>(
+ highest_precision_in_long_double & arbitrary_mask)));
+
+ EXPECT_EQ(static_cast<absl::uint128>(-0.1L), 0);
}
TEST(Uint128, OperatorAssignReturnRef) {