Export of internal Abseil changes

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d35c72d705155dcd89a92835103540f14c643d10 by Gennadiy Rozental <rogeeff@google.com>:

helpxml changed to report types of flags with built-in value type.

PiperOrigin-RevId: 275131440

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f3478792943d7dd40a6ef6083a8e5d374f43a65e by Abseil Team <absl-team@google.com>:

Add space padding tests for hex conversions.

PiperOrigin-RevId: 275120155

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7c2e4725403e173660f33f94af686a75d3722936 by Andy Soffer <asoffer@google.com>:

Fix https://github.com/abseil/abseil-cpp/issues/379
by renaming `roundup` to `round_up`

PiperOrigin-RevId: 275106110

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84cb30d6ee509961ac4359cfdda1360973b9527d by Laramie Leavitt <lar@google.com>:

Move random_internal::wide_multiply into a file by the same name.

PiperOrigin-RevId: 275059359

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06d691a8c187b5d899e7863784b23bdcfd580cb2 by Abseil Team <absl-team@google.com>:

Add missing "return" keyword.

PiperOrigin-RevId: 275036408
GitOrigin-RevId: d35c72d705155dcd89a92835103540f14c643d10
Change-Id: Id837b4de6c9cfe18f0a088363754bfe389df985b

1 files changed, 109 insertions, 0 deletions

diff --git a/absl/random/internal/wide_multiply.h b/absl/random/internal/wide_multiply.h
new file mode 100644
index 000000000000..ebbfa1f2c10e
--- /dev/null
+++ b/absl/random/internal/wide_multiply.h
@@ -0,0 +1,109 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_RANDOM_INTERNAL_WIDE_MULTIPLY_H_
+#define ABSL_RANDOM_INTERNAL_WIDE_MULTIPLY_H_
+
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+
+#if (defined(_WIN32) || defined(_WIN64)) && defined(_M_IA64)
+#include <intrin.h>  // NOLINT(build/include_order)
+#pragma intrinsic(_umul128)
+#define ABSL_INTERNAL_USE_UMUL128 1
+#endif
+
+#include "absl/base/config.h"
+#include "absl/base/internal/bits.h"
+#include "absl/numeric/int128.h"
+#include "absl/random/internal/traits.h"
+
+namespace absl {
+namespace random_internal {
+
+// Helper object to multiply two 64-bit values to a 128-bit value.
+// MultiplyU64ToU128 multiplies two 64-bit values to a 128-bit value.
+// If an intrinsic is available, it is used, otherwise use native 32-bit
+// multiplies to construct the result.
+inline uint128 MultiplyU64ToU128(uint64_t a, uint64_t b) {
+#if defined(ABSL_HAVE_INTRINSIC_INT128)
+  return uint128(static_cast<__uint128_t>(a) * b);
+#elif defined(ABSL_INTERNAL_USE_UMUL128)
+  // uint64_t * uint64_t => uint128 multiply using imul intrinsic on MSVC.
+  uint64_t high = 0;
+  const uint64_t low = _umul128(a, b, &high);
+  return absl::MakeUint128(high, low);
+#else
+  // uint128(a) * uint128(b) in emulated mode computes a full 128-bit x 128-bit
+  // multiply.  However there are many cases where that is not necessary, and it
+  // is only necessary to support a 64-bit x 64-bit = 128-bit multiply.  This is
+  // for those cases.
+  const uint64_t a00 = static_cast<uint32_t>(a);
+  const uint64_t a32 = a >> 32;
+  const uint64_t b00 = static_cast<uint32_t>(b);
+  const uint64_t b32 = b >> 32;
+
+  const uint64_t c00 = a00 * b00;
+  const uint64_t c32a = a00 * b32;
+  const uint64_t c32b = a32 * b00;
+  const uint64_t c64 = a32 * b32;
+
+  const uint32_t carry =
+      static_cast<uint32_t>(((c00 >> 32) + static_cast<uint32_t>(c32a) +
+                             static_cast<uint32_t>(c32b)) >>
+                            32);
+
+  return absl::MakeUint128(c64 + (c32a >> 32) + (c32b >> 32) + carry,
+                           c00 + (c32a << 32) + (c32b << 32));
+#endif
+}
+
+// wide_multiply<T> multiplies two N-bit values to a 2N-bit result.
+template <typename UIntType>
+struct wide_multiply {
+  static constexpr size_t kN = std::numeric_limits<UIntType>::digits;
+  using input_type = UIntType;
+  using result_type = typename random_internal::unsigned_bits<kN * 2>::type;
+
+  static result_type multiply(input_type a, input_type b) {
+    return static_cast<result_type>(a) * b;
+  }
+
+  static input_type hi(result_type r) { return r >> kN; }
+  static input_type lo(result_type r) { return r; }
+
+  static_assert(std::is_unsigned<UIntType>::value,
+                "Class-template wide_multiply<> argument must be unsigned.");
+};
+
+#ifndef ABSL_HAVE_INTRINSIC_INT128
+template <>
+struct wide_multiply<uint64_t> {
+  using input_type = uint64_t;
+  using result_type = uint128;
+
+  static result_type multiply(uint64_t a, uint64_t b) {
+    return MultiplyU64ToU128(a, b);
+  }
+
+  static uint64_t hi(result_type r) { return Uint128High64(r); }
+  static uint64_t lo(result_type r) { return Uint128Low64(r); }
+};
+#endif
+
+}  // namespace random_internal
+}  // namespace absl
+
+#endif  // ABSL_RANDOM_INTERNAL_WIDE_MULTIPLY_H_