From 256be563447a315f2a7993ec669460ba475fa86a Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Tue, 12 Mar 2019 11:39:15 -0700 Subject: Export of internal Abseil changes. -- 00d42e3d5433aaf29c2ed293520b2ba178ae8bdb by Greg Falcon : Import of CCTZ from GitHub. PiperOrigin-RevId: 238061818 -- 867a7ca318fac2991ea9a4107dbae3cc9fbf974a by Abseil Team : Added a IWYU export pragma when including a standard header for the purpose of aliasing its symbols. PiperOrigin-RevId: 238022277 -- 17047745058f2f151cd986ea9f649512542d3876 by Matt Armstrong : Clarify the comment discouraging WrapUnique(x) calls. PiperOrigin-RevId: 237873803 -- 3dcb2e4968243d33ca0ce53280c445df50f4a7ec by Samuel Benzaquen : Workaround clang bug https://bugs.llvm.org/show_bug.cgi?id=38289 PiperOrigin-RevId: 237873551 -- f348d2dc7087a990cbdfb95aa51fd7ff478ae40e by Samuel Benzaquen : Reduce minimum capacity to 1. This reduces memory usage for small tables. A flat_hash_set of 1 element goes from 92 bytes to 24. A flat_hash_set of 1 element goes from 512 bytes to 56. PiperOrigin-RevId: 237859811 -- 9c8125be5e4e5d22a7bb62bdec8c323338385c1b by Jon Cohen : 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 : Import of CCTZ from GitHub. PiperOrigin-RevId: 237714597 GitOrigin-RevId: 00d42e3d5433aaf29c2ed293520b2ba178ae8bdb Change-Id: I5faecc45add4a5a774d4f9baf06e5519091f2ccc --- absl/numeric/int128.cc | 22 ++++++++++++++++++++++ absl/numeric/int128_test.cc | 14 ++++++++++++++ 2 files changed, 36 insertions(+) (limited to 'absl/numeric') diff --git a/absl/numeric/int128.cc b/absl/numeric/int128.cc index 33f528c..93b62c5 100644 --- a/absl/numeric/int128.cc +++ b/absl/numeric/int128.cc @@ -123,6 +123,28 @@ uint128 MakeUint128FromFloat(T v) { return MakeUint128(0, static_cast(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::digits >= 50, ""); + static_assert(std::numeric_limits::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(static_cast(std::trunc(v))); + v = std::ldexp(v - static_cast(w0), 50); + uint64_t w1 = static_cast(static_cast(std::trunc(v))); + v = std::ldexp(v - static_cast(w1), 50); + uint64_t w2 = static_cast(static_cast(std::trunc(v))); + return (static_cast(w0) << 100) | (static_cast(w1) << 50) | + static_cast(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 216ec50..5e1b5ec 100644 --- a/absl/numeric/int128_test.cc +++ b/absl/numeric/int128_test.cc @@ -271,6 +271,20 @@ TEST(Uint128, ConversionTests) { EXPECT_EQ(static_cast(round_to_zero), 0); EXPECT_EQ(static_cast(round_to_five), 5); EXPECT_EQ(static_cast(round_to_nine), 9); + + absl::uint128 highest_precision_in_long_double = + ~absl::uint128{} >> (128 - std::numeric_limits::digits); + EXPECT_EQ(highest_precision_in_long_double, + static_cast( + static_cast(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(static_cast( + highest_precision_in_long_double & arbitrary_mask))); + + EXPECT_EQ(static_cast(-0.1L), 0); } TEST(Uint128, OperatorAssignReturnRef) { -- cgit v1.2.3