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559 lines
17 KiB
C++
559 lines
17 KiB
C++
/*
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* PCG Random Number Generation for C++
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*
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* Copyright 2014-2017 Melissa O'Neill <oneill@pcg-random.org>,
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* and the PCG Project contributors.
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*
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* SPDX-License-Identifier: (Apache-2.0 OR MIT)
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*
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* Licensed under the Apache License, Version 2.0 (provided in
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* LICENSE-APACHE.txt and at http://www.apache.org/licenses/LICENSE-2.0)
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* or under the MIT license (provided in LICENSE-MIT.txt and at
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* http://opensource.org/licenses/MIT), at your option. This file may not
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* be copied, modified, or distributed except according to those terms.
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*
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* Distributed on an "AS IS" BASIS, WITHOUT WARRANTY OF ANY KIND, either
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* express or implied. See your chosen license for details.
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*
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* For additional information about the PCG random number generation scheme,
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* visit http://www.pcg-random.org/.
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*/
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/*
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* This file provides support code that is useful for random-number generation
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* but not specific to the PCG generation scheme, including:
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* - 128-bit int support for platforms where it isn't available natively
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* - bit twiddling operations
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* - I/O of 128-bit and 8-bit integers
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* - Handling the evilness of SeedSeq
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* - Support for efficiently producing random numbers less than a given
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* bound
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*/
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#ifndef PCG_EXTRAS_HPP_INCLUDED
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#define PCG_EXTRAS_HPP_INCLUDED 1
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#include <cinttypes>
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#include <cstddef>
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#include <cstdlib>
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#include <cstring>
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#include <cassert>
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#include <limits>
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#include <iostream>
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#include <type_traits>
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#include <utility>
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#include <locale>
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#include <iterator>
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#ifdef __GNUC__
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#include <cxxabi.h>
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#endif
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// NOLINTBEGIN(readability-identifier-naming, modernize-use-using, bugprone-macro-parentheses, google-explicit-constructor)
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/*
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* Abstractions for compiler-specific directives
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*/
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#ifdef __GNUC__
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#define PCG_NOINLINE __attribute__((noinline))
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#else
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#define PCG_NOINLINE
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#endif
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/*
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* Some members of the PCG library use 128-bit math. When compiling on 64-bit
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* platforms, both GCC and Clang provide 128-bit integer types that are ideal
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* for the job.
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*
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* On 32-bit platforms (or with other compilers), we fall back to a C++
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* class that provides 128-bit unsigned integers instead. It may seem
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* like we're reinventing the wheel here, because libraries already exist
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* that support large integers, but most existing libraries provide a very
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* generic multiprecision code, but here we're operating at a fixed size.
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* Also, most other libraries are fairly heavyweight. So we use a direct
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* implementation. Sadly, it's much slower than hand-coded assembly or
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* direct CPU support.
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*
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*/
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#if __SIZEOF_INT128__
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namespace pcg_extras {
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typedef __uint128_t pcg128_t;
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}
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#define PCG_128BIT_CONSTANT(high,low) \
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((pcg128_t(high) << 64) + low)
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#else
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#include "pcg_uint128.hpp"
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namespace pcg_extras {
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typedef pcg_extras::uint_x4<uint32_t,uint64_t> pcg128_t;
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}
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#define PCG_128BIT_CONSTANT(high,low) \
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pcg128_t(high,low)
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#define PCG_EMULATED_128BIT_MATH 1
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#endif
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namespace pcg_extras {
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/*
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* We often need to represent a "number of bits". When used normally, these
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* numbers are never greater than 128, so an unsigned char is plenty.
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* If you're using a nonstandard generator of a larger size, you can set
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* PCG_BITCOUNT_T to have it define it as a larger size. (Some compilers
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* might produce faster code if you set it to an unsigned int.)
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*/
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#ifndef PCG_BITCOUNT_T
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typedef uint8_t bitcount_t;
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#else
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typedef PCG_BITCOUNT_T bitcount_t;
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#endif
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/*
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* C++ requires us to be able to serialize RNG state by printing or reading
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* it from a stream. Because we use 128-bit ints, we also need to be able
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* or print them, so here is code to do so.
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*
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* This code provides enough functionality to print 128-bit ints in decimal
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* and zero-padded in hex. It's not a full-featured implementation.
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*/
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template <typename CharT, typename Traits>
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std::basic_ostream<CharT,Traits>&
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operator<<(std::basic_ostream<CharT,Traits>& out, pcg128_t value)
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{
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auto desired_base = out.flags() & out.basefield;
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bool want_hex = desired_base == out.hex;
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if (want_hex) {
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uint64_t highpart = uint64_t(value >> 64);
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uint64_t lowpart = uint64_t(value);
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auto desired_width = out.width();
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if (desired_width > 16) {
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out.width(desired_width - 16);
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}
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if (highpart != 0 || desired_width > 16)
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out << highpart;
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CharT oldfill = '\0';
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if (highpart != 0) {
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out.width(16);
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oldfill = out.fill('0');
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}
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auto oldflags = out.setf(decltype(desired_base){}, out.showbase);
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out << lowpart;
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out.setf(oldflags);
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if (highpart != 0) {
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out.fill(oldfill);
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}
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return out;
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}
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constexpr size_t MAX_CHARS_128BIT = 40;
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char buffer[MAX_CHARS_128BIT];
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char* pos = buffer+sizeof(buffer);
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*(--pos) = '\0';
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constexpr auto BASE = pcg128_t(10ULL);
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do {
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auto div = value / BASE;
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auto mod = uint32_t(value - (div * BASE));
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*(--pos) = '0' + char(mod);
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value = div;
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} while(value != pcg128_t(0ULL));
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return out << pos;
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}
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template <typename CharT, typename Traits>
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std::basic_istream<CharT,Traits>&
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operator>>(std::basic_istream<CharT,Traits>& in, pcg128_t& value)
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{
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typename std::basic_istream<CharT,Traits>::sentry s(in);
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if (!s)
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return in;
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constexpr auto BASE = pcg128_t(10ULL);
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pcg128_t current(0ULL);
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bool did_nothing = true;
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bool overflow = false;
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for(;;) {
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CharT wide_ch = in.get();
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if (!in.good())
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break;
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auto ch = in.narrow(wide_ch, '\0');
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if (ch < '0' || ch > '9') {
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in.unget();
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break;
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}
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did_nothing = false;
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pcg128_t digit(uint32_t(ch - '0'));
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pcg128_t timesbase = current*BASE;
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overflow = overflow || timesbase < current;
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current = timesbase + digit;
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overflow = overflow || current < digit;
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}
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if (did_nothing || overflow) {
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in.setstate(std::ios::failbit);
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if (overflow)
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current = ~pcg128_t(0ULL);
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}
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value = current;
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return in;
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}
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/*
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* Likewise, if people use tiny rngs, we'll be serializing uint8_t.
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* If we just used the provided IO operators, they'd read/write chars,
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* not ints, so we need to define our own. We *can* redefine this operator
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* here because we're in our own namespace.
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*/
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template <typename CharT, typename Traits>
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std::basic_ostream<CharT,Traits>&
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operator<<(std::basic_ostream<CharT,Traits>&out, uint8_t value)
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{
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return out << uint32_t(value);
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}
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template <typename CharT, typename Traits>
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std::basic_istream<CharT,Traits>&
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operator>>(std::basic_istream<CharT,Traits>& in, uint8_t& target)
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{
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uint32_t value = 0xdecea5edU;
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in >> value;
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if (!in && value == 0xdecea5edU)
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return in;
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if (value > uint8_t(~0)) {
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in.setstate(std::ios::failbit);
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value = ~0U;
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}
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target = uint8_t(value);
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return in;
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}
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/* Unfortunately, the above functions don't get found in preference to the
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* built in ones, so we create some more specific overloads that will.
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* Ugh.
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*/
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inline std::ostream& operator<<(std::ostream& out, uint8_t value)
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{
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return pcg_extras::operator<< <char>(out, value);
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}
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inline std::istream& operator>>(std::istream& in, uint8_t& value)
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{
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return pcg_extras::operator>> <char>(in, value);
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}
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/*
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* Useful bitwise operations.
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*/
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/*
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* XorShifts are invertable, but they are something of a pain to invert.
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* This function backs them out. It's used by the whacky "inside out"
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* generator defined later.
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*/
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template <typename itype>
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inline itype unxorshift(itype x, bitcount_t bits, bitcount_t shift)
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{
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if (2*shift >= bits) {
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return x ^ (x >> shift);
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}
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itype lowmask1 = (itype(1U) << (bits - shift*2)) - 1;
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itype highmask1 = ~lowmask1;
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itype top1 = x;
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itype bottom1 = x & lowmask1;
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top1 ^= top1 >> shift;
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top1 &= highmask1;
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x = top1 | bottom1;
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itype lowmask2 = (itype(1U) << (bits - shift)) - 1;
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itype bottom2 = x & lowmask2;
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bottom2 = unxorshift(bottom2, bits - shift, shift);
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bottom2 &= lowmask1;
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return top1 | bottom2;
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}
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/*
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* Rotate left and right.
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*
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* In ideal world, compilers would spot idiomatic rotate code and convert it
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* to a rotate instruction. Of course, opinions vary on what the correct
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* idiom is and how to spot it. For clang, sometimes it generates better
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* (but still crappy) code if you define PCG_USE_ZEROCHECK_ROTATE_IDIOM.
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*/
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template <typename itype>
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inline itype rotl(itype value, bitcount_t rot)
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{
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constexpr bitcount_t bits = sizeof(itype) * 8;
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constexpr bitcount_t mask = bits - 1;
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#if defined(PCG_USE_ZEROCHECK_ROTATE_IDIOM)
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return rot ? (value << rot) | (value >> (bits - rot)) : value;
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#else
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return (value << rot) | (value >> ((- rot) & mask));
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#endif
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}
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template <typename itype>
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inline itype rotr(itype value, bitcount_t rot)
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{
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constexpr bitcount_t bits = sizeof(itype) * 8;
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constexpr bitcount_t mask = bits - 1;
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#if defined(PCG_USE_ZEROCHECK_ROTATE_IDIOM)
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return rot ? (value >> rot) | (value << (bits - rot)) : value;
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#else
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return (value >> rot) | (value << ((- rot) & mask));
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#endif
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}
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/* Unfortunately, both Clang and GCC sometimes perform poorly when it comes
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* to properly recognizing idiomatic rotate code, so for we also provide
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* assembler directives (enabled with PCG_USE_INLINE_ASM). Boo, hiss.
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* (I hope that these compilers get better so that this code can die.)
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*
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* These overloads will be preferred over the general template code above.
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*/
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#if defined(PCG_USE_INLINE_ASM) && __GNUC__ && (__x86_64__ || __i386__)
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inline uint8_t rotr(uint8_t value, bitcount_t rot)
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{
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asm ("rorb %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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return value;
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}
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inline uint16_t rotr(uint16_t value, bitcount_t rot)
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{
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asm ("rorw %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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return value;
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}
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inline uint32_t rotr(uint32_t value, bitcount_t rot)
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{
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asm ("rorl %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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return value;
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}
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#if __x86_64__
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inline uint64_t rotr(uint64_t value, bitcount_t rot)
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{
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asm ("rorq %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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return value;
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}
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#endif // __x86_64__
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#endif // PCG_USE_INLINE_ASM
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/*
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* The C++ SeedSeq concept (modelled by seed_seq) can fill an array of
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* 32-bit integers with seed data, but sometimes we want to produce
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* larger or smaller integers.
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*
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* The following code handles this annoyance.
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*
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* uneven_copy will copy an array of 32-bit ints to an array of larger or
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* smaller ints (actually, the code is general it only needing forward
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* iterators). The copy is identical to the one that would be performed if
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* we just did memcpy on a standard little-endian machine, but works
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* regardless of the endian of the machine (or the weirdness of the ints
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* involved).
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*
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* generate_to initializes an array of integers using a SeedSeq
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* object. It is given the size as a static constant at compile time and
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* tries to avoid memory allocation. If we're filling in 32-bit constants
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* we just do it directly. If we need a separate buffer and it's small,
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* we allocate it on the stack. Otherwise, we fall back to heap allocation.
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* Ugh.
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*
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* generate_one produces a single value of some integral type using a
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* SeedSeq object.
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*/
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/* uneven_copy helper, case where destination ints are less than 32 bit. */
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template<class SrcIter, class DestIter>
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SrcIter uneven_copy_impl(
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SrcIter src_first, DestIter dest_first, DestIter dest_last,
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std::true_type)
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{
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typedef typename std::iterator_traits<SrcIter>::value_type src_t;
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typedef typename std::iterator_traits<DestIter>::value_type dest_t;
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constexpr bitcount_t SRC_SIZE = sizeof(src_t);
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constexpr bitcount_t DEST_SIZE = sizeof(dest_t);
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constexpr bitcount_t DEST_BITS = DEST_SIZE * 8;
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constexpr bitcount_t SCALE = SRC_SIZE / DEST_SIZE;
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size_t count = 0;
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src_t value = 0;
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while (dest_first != dest_last) {
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if ((count++ % SCALE) == 0)
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value = *src_first++; // Get more bits
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else
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value >>= DEST_BITS; // Move down bits
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*dest_first++ = dest_t(value); // Truncates, ignores high bits.
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}
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return src_first;
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}
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/* uneven_copy helper, case where destination ints are more than 32 bit. */
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template<class SrcIter, class DestIter>
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SrcIter uneven_copy_impl(
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SrcIter src_first, DestIter dest_first, DestIter dest_last,
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std::false_type)
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{
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typedef typename std::iterator_traits<SrcIter>::value_type src_t;
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typedef typename std::iterator_traits<DestIter>::value_type dest_t;
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constexpr auto SRC_SIZE = sizeof(src_t);
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constexpr auto SRC_BITS = SRC_SIZE * 8;
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constexpr auto DEST_SIZE = sizeof(dest_t);
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constexpr auto SCALE = (DEST_SIZE+SRC_SIZE-1) / SRC_SIZE;
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while (dest_first != dest_last) {
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dest_t value(0UL);
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unsigned int shift = 0;
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for (size_t i = 0; i < SCALE; ++i) {
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value |= dest_t(*src_first++) << shift;
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shift += SRC_BITS;
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}
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*dest_first++ = value;
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}
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return src_first;
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}
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/* uneven_copy, call the right code for larger vs. smaller */
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template<class SrcIter, class DestIter>
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inline SrcIter uneven_copy(SrcIter src_first,
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DestIter dest_first, DestIter dest_last)
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{
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typedef typename std::iterator_traits<SrcIter>::value_type src_t;
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typedef typename std::iterator_traits<DestIter>::value_type dest_t;
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constexpr bool DEST_IS_SMALLER = sizeof(dest_t) < sizeof(src_t);
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return uneven_copy_impl(src_first, dest_first, dest_last,
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std::integral_constant<bool, DEST_IS_SMALLER>{});
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}
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template <typename RngType>
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auto bounded_rand(RngType& rng, typename RngType::result_type upper_bound)
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-> typename RngType::result_type
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{
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typedef typename RngType::result_type rtype;
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rtype threshold = (RngType::max() - RngType::min() + rtype(1) - upper_bound)
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% upper_bound;
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for (;;) {
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rtype r = rng() - RngType::min();
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if (r >= threshold)
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return r % upper_bound;
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}
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}
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template <typename Iter, typename RandType>
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void shuffle(Iter from, Iter to, RandType&& rng) // NOLINT(cppcoreguidelines-missing-std-forward)
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{
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typedef typename std::iterator_traits<Iter>::difference_type delta_t;
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typedef typename std::remove_reference<RandType>::type::result_type result_t;
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auto count = to - from;
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while (count > 1) {
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delta_t chosen = delta_t(bounded_rand(rng, result_t(count)));
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--count;
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--to;
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using std::swap;
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swap(*(from + chosen), *to);
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}
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}
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/*
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* Although std::seed_seq is useful, it isn't everything. Often we want to
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* initialize a random-number generator some other way, such as from a random
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* device.
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*
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* Technically, it does not meet the requirements of a SeedSequence because
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* it lacks some of the rarely-used member functions (some of which would
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* be impossible to provide). However the C++ standard is quite specific
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* that actual engines only called the generate method, so it ought not to be
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* a problem in practice.
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*/
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template <typename RngType>
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class seed_seq_from {
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private:
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RngType rng_;
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typedef uint_least32_t result_type;
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public:
|
|
template<typename... Args>
|
|
seed_seq_from(Args&&... args) :
|
|
rng_(std::forward<Args>(args)...)
|
|
{
|
|
// Nothing (else) to do...
|
|
}
|
|
|
|
template<typename Iter>
|
|
void generate(Iter start, Iter finish)
|
|
{
|
|
for (auto i = start; i != finish; ++i)
|
|
*i = result_type(rng_());
|
|
}
|
|
|
|
constexpr size_t size() const
|
|
{
|
|
return (sizeof(typename RngType::result_type) > sizeof(result_type)
|
|
&& RngType::max() > ~size_t(0UL))
|
|
? ~size_t(0UL)
|
|
: size_t(RngType::max());
|
|
}
|
|
};
|
|
|
|
// Sometimes, when debugging or testing, it's handy to be able print the name
|
|
// of a (in human-readable form). This code allows the idiom:
|
|
//
|
|
// cout << printable_typename<my_foo_type_t>()
|
|
//
|
|
// to print out my_foo_type_t (or its concrete type if it is a synonym)
|
|
|
|
#if __cpp_rtti || __GXX_RTTI
|
|
|
|
template <typename T>
|
|
struct printable_typename {};
|
|
|
|
template <typename T>
|
|
std::ostream& operator<<(std::ostream& out, printable_typename<T>) {
|
|
const char *implementation_typename = typeid(T).name();
|
|
#ifdef __GNUC__
|
|
int status;
|
|
char* pretty_name =
|
|
abi::__cxa_demangle(implementation_typename, nullptr, nullptr, &status);
|
|
if (status == 0)
|
|
out << pretty_name;
|
|
free(static_cast<void*>(pretty_name));
|
|
if (status == 0)
|
|
return out;
|
|
#endif
|
|
out << implementation_typename;
|
|
return out;
|
|
}
|
|
|
|
#endif // __cpp_rtti || __GXX_RTTI
|
|
|
|
} // namespace pcg_extras
|
|
|
|
// NOLINTEND(readability-identifier-naming, modernize-use-using, bugprone-macro-parentheses, google-explicit-constructor)
|
|
|
|
#endif // PCG_EXTRAS_HPP_INCLUDED
|