summaryrefslogtreecommitdiff
path: root/absl/random/log_uniform_int_distribution.h
diff options
context:
space:
mode:
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/log_uniform_int_distribution.h
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
Diffstat (limited to 'absl/random/log_uniform_int_distribution.h')
-rw-r--r--absl/random/log_uniform_int_distribution.h250
1 files changed, 250 insertions, 0 deletions
diff --git a/absl/random/log_uniform_int_distribution.h b/absl/random/log_uniform_int_distribution.h
new file mode 100644
index 00000000..ac43416e
--- /dev/null
+++ b/absl/random/log_uniform_int_distribution.h
@@ -0,0 +1,250 @@
+// 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_LOG_UNIFORM_INT_DISTRIBUTION_H_
+#define ABSL_RANDOM_LOG_UNIFORM_INT_DISTRIBUTION_H_
+
+#include <algorithm>
+#include <cassert>
+#include <cmath>
+#include <istream>
+#include <limits>
+#include <ostream>
+#include <type_traits>
+
+#include "absl/random/internal/distribution_impl.h"
+#include "absl/random/internal/fastmath.h"
+#include "absl/random/internal/iostream_state_saver.h"
+#include "absl/random/internal/traits.h"
+#include "absl/random/uniform_int_distribution.h"
+
+namespace absl {
+
+// log_uniform_int_distribution:
+//
+// Returns a random variate R in range [min, max] such that
+// floor(log(R-min, base)) is uniformly distributed.
+// We ensure uniformity by discretization using the
+// boundary sets [0, 1, base, base * base, ... min(base*n, max)]
+//
+template <typename IntType = int>
+class log_uniform_int_distribution {
+ private:
+ using unsigned_type =
+ typename random_internal::make_unsigned_bits<IntType>::type;
+
+ public:
+ using result_type = IntType;
+
+ class param_type {
+ public:
+ using distribution_type = log_uniform_int_distribution;
+
+ explicit param_type(
+ result_type min = 0,
+ result_type max = (std::numeric_limits<result_type>::max)(),
+ result_type base = 2)
+ : min_(min),
+ max_(max),
+ base_(base),
+ range_(static_cast<unsigned_type>(max_) -
+ static_cast<unsigned_type>(min_)),
+ log_range_(0) {
+ assert(max_ >= min_);
+ assert(base_ > 1);
+
+ if (base_ == 2) {
+ // Determine where the first set bit is on range(), giving a log2(range)
+ // value which can be used to construct bounds.
+ log_range_ = (std::min)(random_internal::LeadingSetBit(range()),
+ std::numeric_limits<unsigned_type>::digits);
+ } else {
+ // NOTE: Computing the logN(x) introduces error from 2 sources:
+ // 1. Conversion of int to double loses precision for values >=
+ // 2^53, which may cause some log() computations to operate on
+ // different values.
+ // 2. The error introduced by the division will cause the result
+ // to differ from the expected value.
+ //
+ // Thus a result which should equal K may equal K +/- epsilon,
+ // which can eliminate some values depending on where the bounds fall.
+ const double inv_log_base = 1.0 / std::log(base_);
+ const double log_range = std::log(static_cast<double>(range()) + 0.5);
+ log_range_ = static_cast<int>(std::ceil(inv_log_base * log_range));
+ }
+ }
+
+ result_type(min)() const { return min_; }
+ result_type(max)() const { return max_; }
+ result_type base() const { return base_; }
+
+ friend bool operator==(const param_type& a, const param_type& b) {
+ return a.min_ == b.min_ && a.max_ == b.max_ && a.base_ == b.base_;
+ }
+
+ friend bool operator!=(const param_type& a, const param_type& b) {
+ return !(a == b);
+ }
+
+ private:
+ friend class log_uniform_int_distribution;
+
+ int log_range() const { return log_range_; }
+ unsigned_type range() const { return range_; }
+
+ result_type min_;
+ result_type max_;
+ result_type base_;
+ unsigned_type range_; // max - min
+ int log_range_; // ceil(logN(range_))
+
+ static_assert(std::is_integral<IntType>::value,
+ "Class-template absl::log_uniform_int_distribution<> must be "
+ "parameterized using an integral type.");
+ };
+
+ log_uniform_int_distribution() : log_uniform_int_distribution(0) {}
+
+ explicit log_uniform_int_distribution(
+ result_type min,
+ result_type max = (std::numeric_limits<result_type>::max)(),
+ result_type base = 2)
+ : param_(min, max, base) {}
+
+ explicit log_uniform_int_distribution(const param_type& p) : param_(p) {}
+
+ void reset() {}
+
+ // generating functions
+ template <typename URBG>
+ result_type operator()(URBG& g) { // NOLINT(runtime/references)
+ return (*this)(g, param_);
+ }
+
+ template <typename URBG>
+ result_type operator()(URBG& g, // NOLINT(runtime/references)
+ const param_type& p) {
+ return (p.min)() + Generate(g, p);
+ }
+
+ result_type(min)() const { return (param_.min)(); }
+ result_type(max)() const { return (param_.max)(); }
+ result_type base() const { return param_.base(); }
+
+ param_type param() const { return param_; }
+ void param(const param_type& p) { param_ = p; }
+
+ friend bool operator==(const log_uniform_int_distribution& a,
+ const log_uniform_int_distribution& b) {
+ return a.param_ == b.param_;
+ }
+ friend bool operator!=(const log_uniform_int_distribution& a,
+ const log_uniform_int_distribution& b) {
+ return a.param_ != b.param_;
+ }
+
+ private:
+ // Returns a log-uniform variate in the range [0, p.range()]. The caller
+ // should add min() to shift the result to the correct range.
+ template <typename URNG>
+ unsigned_type Generate(URNG& g, // NOLINT(runtime/references)
+ const param_type& p);
+
+ param_type param_;
+};
+
+template <typename IntType>
+template <typename URBG>
+typename log_uniform_int_distribution<IntType>::unsigned_type
+log_uniform_int_distribution<IntType>::Generate(
+ URBG& g, // NOLINT(runtime/references)
+ const param_type& p) {
+ // sample e over [0, log_range]. Map the results of e to this:
+ // 0 => 0
+ // 1 => [1, b-1]
+ // 2 => [b, (b^2)-1]
+ // n => [b^(n-1)..(b^n)-1]
+ const int e = absl::uniform_int_distribution<int>(0, p.log_range())(g);
+ if (e == 0) {
+ return 0;
+ }
+ const int d = e - 1;
+
+ unsigned_type base_e, top_e;
+ if (p.base() == 2) {
+ base_e = static_cast<unsigned_type>(1) << d;
+
+ top_e = (e >= std::numeric_limits<unsigned_type>::digits)
+ ? (std::numeric_limits<unsigned_type>::max)()
+ : (static_cast<unsigned_type>(1) << e) - 1;
+ } else {
+ const double r = std::pow(p.base(), d);
+ const double s = (r * p.base()) - 1.0;
+
+ base_e = (r > (std::numeric_limits<unsigned_type>::max)())
+ ? (std::numeric_limits<unsigned_type>::max)()
+ : static_cast<unsigned_type>(r);
+
+ top_e = (s > (std::numeric_limits<unsigned_type>::max)())
+ ? (std::numeric_limits<unsigned_type>::max)()
+ : static_cast<unsigned_type>(s);
+ }
+
+ const unsigned_type lo = (base_e >= p.range()) ? p.range() : base_e;
+ const unsigned_type hi = (top_e >= p.range()) ? p.range() : top_e;
+
+ // choose uniformly over [lo, hi]
+ return absl::uniform_int_distribution<result_type>(lo, hi)(g);
+}
+
+template <typename CharT, typename Traits, typename IntType>
+std::basic_ostream<CharT, Traits>& operator<<(
+ std::basic_ostream<CharT, Traits>& os, // NOLINT(runtime/references)
+ const log_uniform_int_distribution<IntType>& x) {
+ using stream_type =
+ typename random_internal::stream_format_type<IntType>::type;
+ auto saver = random_internal::make_ostream_state_saver(os);
+ os << static_cast<stream_type>((x.min)()) << os.fill()
+ << static_cast<stream_type>((x.max)()) << os.fill()
+ << static_cast<stream_type>(x.base());
+ return os;
+}
+
+template <typename CharT, typename Traits, typename IntType>
+std::basic_istream<CharT, Traits>& operator>>(
+ std::basic_istream<CharT, Traits>& is, // NOLINT(runtime/references)
+ log_uniform_int_distribution<IntType>& x) { // NOLINT(runtime/references)
+ using param_type = typename log_uniform_int_distribution<IntType>::param_type;
+ using result_type =
+ typename log_uniform_int_distribution<IntType>::result_type;
+ using stream_type =
+ typename random_internal::stream_format_type<IntType>::type;
+
+ stream_type min;
+ stream_type max;
+ stream_type base;
+
+ auto saver = random_internal::make_istream_state_saver(is);
+ is >> min >> max >> base;
+ if (!is.fail()) {
+ x.param(param_type(static_cast<result_type>(min),
+ static_cast<result_type>(max),
+ static_cast<result_type>(base)));
+ }
+ return is;
+}
+
+} // namespace absl
+
+#endif // ABSL_RANDOM_LOG_UNIFORM_INT_DISTRIBUTION_H_