bench hash table

bench_hash.d

import std.file, std.algorithm, std.stdio, std.random, std.math;

extern (C++)
{
    struct StringValue
    {
        void *ptrvalue;
        size_t length;
        char[0] lstring;
    }

    void tab_init();
    StringValue *tab_update(const char * key, size_t len);
    void tab_report();
}

// exponential distribution around mean
struct ExpRandom
{
    double mean;
    Random gen;

    this(double mean)
    {
        this.mean = mean;
        gen = Random(unpredictableSeed);
    }

    size_t front()
    {
        return lround(mean * -log(uniform!"()"(0.0, 1.0, gen)));
    }

    alias gen this;
}

struct CacheStomper
{
    ExpRandom rnd;
    size_t i;
    ubyte[] mem;

    this(size_t avgBytesPerCall)
    {
        rnd = ExpRandom(avgBytesPerCall / 64.0);
        mem = new ubyte[](32 * 1024 * 1024);
    }

    void stomp()
    {
        immutable n = rnd.front(); rnd.popFront();
        foreach (_; 0 .. n)
            ++mem[(i += 64) & ($ - 1)];
    }
}

void main()
{
    immutable text = cast(string)read("dante.txt");
    tab_init();
    auto stomper = CacheStomper(1000);
    foreach (_; 0 .. 20)
    {
        foreach (word; text.splitter(' '))
        {
            auto sv = tab_update(word.ptr, word.length);
            ++sv.ptrvalue;
            stomper.stomp();
        }
    }
    //tab_report();
}