source: doc/theses/thierry_delisle_PhD/code/utils.hpp@ b9fa85b

#pragma once

#include <cassert>
#include <cstddef>
#include <atomic>
#include <chrono>
#include <fstream>
#include <iostream>

#include <unistd.h>
#include <sys/sysinfo.h>

#include <x86intrin.h>

// Barrier from
class barrier_t {
public:
        barrier_t(size_t total)
                : waiting(0)
                , total(total)
        {}

        void wait(unsigned) {
                size_t target = waiting++;
                target = (target - (target % total)) + total;
                while(waiting < target)
                        asm volatile("pause");

                assert(waiting < (1ul << 60));
        }

private:
        std::atomic<size_t> waiting;
        size_t total;
};

// class Random {
// private:
//      unsigned int seed;
// public:
//      Random(int seed) {
//              this->seed = seed;
//      }

//      /** returns pseudorandom x satisfying 0 <= x < n. **/
//      unsigned int next() {
//              seed ^= seed << 6;
//              seed ^= seed >> 21;
//              seed ^= seed << 7;
//              return seed;
//      }
// };

constexpr uint64_t extendedEuclidY(uint64_t a, uint64_t b);
constexpr uint64_t extendedEuclidX(uint64_t a, uint64_t b){
    return (b==0) ? 1 : extendedEuclidY(b, a - b * (a / b));
}
constexpr uint64_t extendedEuclidY(uint64_t a, uint64_t b){
    return (b==0) ? 0 : extendedEuclidX(b, a - b * (a / b)) - (a / b) * extendedEuclidY(b, a - b * (a / b));
}

class Random {
private:
        uint64_t x;

        static constexpr const uint64_t M  = 1ul << 48ul;
        static constexpr const uint64_t A  = 25214903917;
        static constexpr const uint64_t C  = 11;
        static constexpr const uint64_t D  = 16;

public:
        static constexpr const uint64_t m  = M;
        static constexpr const uint64_t a  = A;
        static constexpr const uint64_t c  = C;
        static constexpr const uint64_t d  = D;
        static constexpr const uint64_t ai = extendedEuclidX(A, M);
public:
        Random(unsigned int seed) {
                this->x = seed * a;
        }

        /** returns pseudorandom x satisfying 0 <= x < n. **/
        unsigned int next() {
                //nextx = (a * x + c) % m;
                x = (A * x + C) & (M - 1);
                return x >> D;
        }
        unsigned int prev() {
                //prevx = (ainverse * (x - c)) mod m
                unsigned int r = x >> D;
                x = ai * (x - C) & (M - 1);
                return r;
        }

        void set_raw_state(uint64_t _x) {
                this->x = _x;
        }

        uint64_t get_raw_state() {
                return this->x;
        }
};

static inline long long rdtscl(void) {
    unsigned int lo, hi;
    __asm__ __volatile__ ("rdtsc" : "=a"(lo), "=d"(hi));
    return ( (unsigned long long)lo)|( ((unsigned long long)hi)<<32 );
}

static inline void affinity(int tid) {
        static int cpus = get_nprocs();

        cpu_set_t  mask;
        CPU_ZERO(&mask);
        int cpu = cpus - tid;  // Set CPU affinity to tid, starting from the end
        CPU_SET(cpu, &mask);
        auto result = sched_setaffinity(0, sizeof(mask), &mask);
        if(result != 0) {
                std::cerr << "Affinity set failed with " << result<< ", wanted " << cpu << std::endl;
        }
}

static const constexpr std::size_t cache_line_size = 64;
static inline void check_cache_line_size() {
        std::cout << "Checking cache line size" << std::endl;
        const std::string cache_file = "/sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size";

        std::ifstream ifs (cache_file, std::ifstream::in);

        if(!ifs.good()) {
                std::cerr << "Could not open file to check cache line size" << std::endl;
                std::cerr << "Looking for: " << cache_file << std::endl;
                std::exit(2);
        }

        size_t got;
        ifs >> got;

        ifs.close();

        if(cache_line_size != got) {
                std::cerr << "Cache line has incorrect size : " << got << std::endl;
                std::exit(1);
        }

        std::cout << "Done" << std::endl;
}

using Clock = std::chrono::high_resolution_clock;
using duration_t = std::chrono::duration<double>;
using std::chrono::nanoseconds;

template<typename Ratio, typename T>
T duration_cast(T seconds) {
        return std::chrono::duration_cast<std::chrono::duration<T, Ratio>>(std::chrono::duration<T>(seconds)).count();
}

static inline unsigned rand_bit(unsigned rnum, size_t mask) __attribute__((artificial));
static inline unsigned rand_bit(unsigned rnum, size_t mask) {
        unsigned bit = mask ? rnum % __builtin_popcountl(mask) : 0;
#if !defined(__BMI2__)
        uint64_t v = mask;   // Input value to find position with rank r.
        unsigned int r = bit + 1;// Input: bit's desired rank [1-64].
        unsigned int s;      // Output: Resulting position of bit with rank r [1-64]
        uint64_t a, b, c, d; // Intermediate temporaries for bit count.
        unsigned int t;      // Bit count temporary.

        // Do a normal parallel bit count for a 64-bit integer,
        // but store all intermediate steps.
        a =  v - ((v >> 1) & ~0UL/3);
        b = (a & ~0UL/5) + ((a >> 2) & ~0UL/5);
        c = (b + (b >> 4)) & ~0UL/0x11;
        d = (c + (c >> 8)) & ~0UL/0x101;


        t = (d >> 32) + (d >> 48);
        // Now do branchless select!
        s  = 64;
        s -= ((t - r) & 256) >> 3; r -= (t & ((t - r) >> 8));
        t  = (d >> (s - 16)) & 0xff;
        s -= ((t - r) & 256) >> 4; r -= (t & ((t - r) >> 8));
        t  = (c >> (s - 8)) & 0xf;
        s -= ((t - r) & 256) >> 5; r -= (t & ((t - r) >> 8));
        t  = (b >> (s - 4)) & 0x7;
        s -= ((t - r) & 256) >> 6; r -= (t & ((t - r) >> 8));
        t  = (a >> (s - 2)) & 0x3;
        s -= ((t - r) & 256) >> 7; r -= (t & ((t - r) >> 8));
        t  = (v >> (s - 1)) & 0x1;
        s -= ((t - r) & 256) >> 8;
        return s - 1;
#else
        uint64_t picked = _pdep_u64(1ul << bit, mask);
        return picked ? __builtin_ctzl(picked) : 0;
#endif
}

struct spinlock_t {
        std::atomic_bool ll = { false };

        inline void lock() {
                while( __builtin_expect(ll.exchange(true),false) ) {
                        while(ll.load(std::memory_order_relaxed))
                                asm volatile("pause");
                }
        }

        inline bool try_lock() {
                return false == ll.exchange(true);
        }

        inline void unlock() {
                ll.store(false, std::memory_order_release);
        }

        inline explicit operator bool() {
                return ll.load(std::memory_order_relaxed);
        }
};

static inline bool bts(std::atomic_size_t & target, size_t bit ) {
        //*
        int result = 0;
        asm volatile(
                "LOCK btsq %[bit], %[target]\n\t"
                :"=@ccc" (result)
                : [target] "m" (target), [bit] "r" (bit)
        );
        return result != 0;
        /*/
        size_t mask = 1ul << bit;
        size_t ret = target.fetch_or(mask, std::memory_order_relaxed);
        return (ret & mask) != 0;
        //*/
}

static inline bool btr(std::atomic_size_t & target, size_t bit ) {
        //*
        int result = 0;
        asm volatile(
                "LOCK btrq %[bit], %[target]\n\t"
                :"=@ccc" (result)
                : [target] "m" (target), [bit] "r" (bit)
        );
        return result != 0;
        /*/
        size_t mask = 1ul << bit;
        size_t ret = target.fetch_and(~mask, std::memory_order_relaxed);
        return (ret & mask) != 0;
        //*/
}