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authorGravatar Abseil Team <absl-team@google.com>2019-06-21 13:11:42 -0700
committerGravatar Gennadiy Rozental <rogeeff@google.com>2019-06-21 16:18:10 -0400
commite9324d926a9189e222741fce6e676f0944661a72 (patch)
treea08568a709940c376454da34c9d8aac021378e5f /absl/random/discrete_distribution.cc
parent43ef2148c0936ebf7cb4be6b19927a9d9d145b8f (diff)
Export of internal Abseil changes.
-- 7a6ff16a85beb730c172d5d25cf1b5e1be885c56 by Laramie Leavitt <lar@google.com>: Internal change. PiperOrigin-RevId: 254454546 -- ff8f9bafaefc26d451f576ea4a06d150aed63f6f by Andy Soffer <asoffer@google.com>: Internal changes PiperOrigin-RevId: 254451562 -- deefc5b651b479ce36f0b4ef203e119c0c8936f2 by CJ Johnson <johnsoncj@google.com>: Account for subtracting unsigned values from the size of InlinedVector PiperOrigin-RevId: 254450625 -- 3c677316a27bcadc17e41957c809ca472d5fef14 by Andy Soffer <asoffer@google.com>: Add C++17's std::make_from_tuple to absl/utility/utility.h PiperOrigin-RevId: 254411573 -- 4ee3536a918830eeec402a28fc31a62c7c90b940 by CJ Johnson <johnsoncj@google.com>: Adds benchmark for the rest of the InlinedVector public API PiperOrigin-RevId: 254408378 -- e5a21a00700ee83498ff1efbf649169756463ee4 by CJ Johnson <johnsoncj@google.com>: Updates the definition of InlinedVector::shrink_to_fit() to be exception safe and adds exception safety tests for it. PiperOrigin-RevId: 254401387 -- 2ea82e72b86d82d78b4e4712a63a55981b53c64b by Laramie Leavitt <lar@google.com>: Use absl::InsecureBitGen in place of std::mt19937 in tests absl/random/...distribution_test.cc PiperOrigin-RevId: 254289444 -- fa099e02c413a7ffda732415e8105cad26a90337 by Andy Soffer <asoffer@google.com>: Internal changes PiperOrigin-RevId: 254286334 -- ce34b7f36933b30cfa35b9c9a5697a792b5666e4 by Andy Soffer <asoffer@google.com>: Internal changes PiperOrigin-RevId: 254273059 -- 6f9c473da7c2090c2e85a37c5f00622e8a912a89 by Jorg Brown <jorg@google.com>: Change absl::container_internal::CompressedTuple to instantiate its internal Storage class with the name of the type it's holding, rather than the name of the Tuple. This is not an externally-visible change, other than less compiler memory is used and less debug information is generated. PiperOrigin-RevId: 254269285 -- 8bd3c186bf2fc0c55d8a2dd6f28a5327502c9fba by Andy Soffer <asoffer@google.com>: Adding short-hand IntervalClosed for IntervalClosedClosed and IntervalOpen for IntervalOpenOpen. PiperOrigin-RevId: 254252419 -- ea957f99b6a04fccd42aa05605605f3b44b1ecfd by Abseil Team <absl-team@google.com>: Do not directly use __SIZEOF_INT128__. In order to avoid linker errors when building with clang-cl (__fixunsdfti, __udivti3 and __fixunssfti are undefined), this CL uses ABSL_HAVE_INTRINSIC_INT128 which is not defined for clang-cl. PiperOrigin-RevId: 254250739 -- 89ab385cd26b34d64130bce856253aaba96d2345 by Andy Soffer <asoffer@google.com>: Internal changes PiperOrigin-RevId: 254242321 -- cffc793d93eca6d6bdf7de733847b6ab4a255ae9 by CJ Johnson <johnsoncj@google.com>: Adds benchmark for InlinedVector::reserve(size_type) PiperOrigin-RevId: 254199226 -- c90c7a9fa3c8f0c9d5114036979548b055ea2f2a by Gennadiy Rozental <rogeeff@google.com>: Import of CCTZ from GitHub. PiperOrigin-RevId: 254072387 -- c4c388beae016c9570ab54ffa1d52660e4a85b7b by Laramie Leavitt <lar@google.com>: Internal cleanup. PiperOrigin-RevId: 254062381 -- d3c992e221cc74e5372d0c8fa410170b6a43c062 by Tom Manshreck <shreck@google.com>: Update distributions.h to Abseil standards PiperOrigin-RevId: 254054946 -- d15ad0035c34ef11b14fadc5a4a2d3ec415f5518 by CJ Johnson <johnsoncj@google.com>: Removes functions with only one caller from the implementation details of InlinedVector by manually inlining the definitions PiperOrigin-RevId: 254005427 -- 2f37e807efc3a8ef1f4b539bdd379917d4151520 by Andy Soffer <asoffer@google.com>: Initial release of Abseil Random PiperOrigin-RevId: 253999861 -- 24ed1694b6430791d781ed533a8f8ccf6cac5856 by CJ Johnson <johnsoncj@google.com>: Updates the definition of InlinedVector::assign(...)/InlinedVector::operator=(...) to new, exception-safe implementations with exception safety tests to boot PiperOrigin-RevId: 253993691 -- 5613d95f5a7e34a535cfaeadce801441e990843e by CJ Johnson <johnsoncj@google.com>: Adds benchmarks for InlinedVector::shrink_to_fit() PiperOrigin-RevId: 253989647 -- 2a96ddfdac40bbb8cb6a7f1aeab90917067c6e63 by Abseil Team <absl-team@google.com>: Initial release of Abseil Random PiperOrigin-RevId: 253927497 -- bf1aff8fc9ffa921ad74643e9525ecf25b0d8dc1 by Andy Soffer <asoffer@google.com>: Initial release of Abseil Random PiperOrigin-RevId: 253920512 -- bfc03f4a3dcda3cf3a4b84bdb84cda24e3394f41 by Laramie Leavitt <lar@google.com>: Internal change. PiperOrigin-RevId: 253886486 -- 05036cfcc078ca7c5f581a00dfb0daed568cbb69 by Eric Fiselier <ericwf@google.com>: Don't include `winsock2.h` because it drags in `windows.h` and friends, and they define awful macros like OPAQUE, ERROR, and more. This has the potential to break abseil users. Instead we only forward declare `timeval` and require Windows users include `winsock2.h` themselves. This is both inconsistent and poor QoI, but so including 'windows.h' is bad too. PiperOrigin-RevId: 253852615 GitOrigin-RevId: 7a6ff16a85beb730c172d5d25cf1b5e1be885c56 Change-Id: Icd6aff87da26f29ec8915da856f051129987cef6
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+// 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.
+
+#include "absl/random/discrete_distribution.h"
+
+namespace absl {
+namespace random_internal {
+
+// Initializes the distribution table for Walker's Aliasing algorithm, described
+// in Knuth, Vol 2. as well as in https://en.wikipedia.org/wiki/Alias_method
+std::vector<std::pair<double, size_t>> InitDiscreteDistribution(
+ std::vector<double>* probabilities) {
+ // The empty-case should already be handled by the constructor.
+ assert(probabilities);
+ assert(!probabilities->empty());
+
+ // Step 1. Normalize the input probabilities to 1.0.
+ double sum = std::accumulate(std::begin(*probabilities),
+ std::end(*probabilities), 0.0);
+ if (std::fabs(sum - 1.0) > 1e-6) {
+ // Scale `probabilities` only when the sum is too far from 1.0. Scaling
+ // unconditionally will alter the probabilities slightly.
+ for (double& item : *probabilities) {
+ item = item / sum;
+ }
+ }
+
+ // Step 2. At this point `probabilities` is set to the conditional
+ // probabilities of each element which sum to 1.0, to within reasonable error.
+ // These values are used to construct the proportional probability tables for
+ // the selection phases of Walker's Aliasing algorithm.
+ //
+ // To construct the table, pick an element which is under-full (i.e., an
+ // element for which `(*probabilities)[i] < 1.0/n`), and pair it with an
+ // element which is over-full (i.e., an element for which
+ // `(*probabilities)[i] > 1.0/n`). The smaller value can always be retired.
+ // The larger may still be greater than 1.0/n, or may now be less than 1.0/n,
+ // and put back onto the appropriate collection.
+ const size_t n = probabilities->size();
+ std::vector<std::pair<double, size_t>> q;
+ q.reserve(n);
+
+ std::vector<size_t> over;
+ std::vector<size_t> under;
+ size_t idx = 0;
+ for (const double item : *probabilities) {
+ assert(item >= 0);
+ const double v = item * n;
+ q.emplace_back(v, 0);
+ if (v < 1.0) {
+ under.push_back(idx++);
+ } else {
+ over.push_back(idx++);
+ }
+ }
+ while (!over.empty() && !under.empty()) {
+ auto lo = under.back();
+ under.pop_back();
+ auto hi = over.back();
+ over.pop_back();
+
+ q[lo].second = hi;
+ const double r = q[hi].first - (1.0 - q[lo].first);
+ q[hi].first = r;
+ if (r < 1.0) {
+ under.push_back(hi);
+ } else {
+ over.push_back(hi);
+ }
+ }
+
+ // Due to rounding errors, there may be un-paired elements in either
+ // collection; these should all be values near 1.0. For these values, set `q`
+ // to 1.0 and set the alternate to the identity.
+ for (auto i : over) {
+ q[i] = {1.0, i};
+ }
+ for (auto i : under) {
+ q[i] = {1.0, i};
+ }
+ return q;
+}
+
+} // namespace random_internal
+} // namespace absl