floppsyhash.cpp

// Copyright 2020 Cris Stringfellow
// Licensed under GPL-3.0
// https://github.com/dosyago/floppsy
#define _USE_MATH_DEFINES
#include <math.h>
#include "floppsyhash.h"

#if defined(_MSC_VER)

#define FORCE_INLINE	__forceinline

// Other compilers

#else	// defined(_MSC_VER)

#define	FORCE_INLINE inline __attribute__((always_inline))

#endif // !defined(_MSC_VER)

//---------
// Q function : Continued Egyptian Fraction update function

FORCE_INLINE void q ( double * state, double key_val, 
         double numerator, double denominator )
{
  state[0] += numerator / denominator;
  state[0] = 1.0 / state[0];

  state[1] += key_val + M_PI;
  state[1] = numerator / state[1];
}

//---------
// round function : process the message 

FORCE_INLINE void round ( const uint8_t * msg, long len, 
            double * state ) 
{
  double numerator = 1.0;

  // Loop
  for( long i = 0; i < len; i++ ) {
    double val = (double)msg[i];
    double denominator = (M_E * val + i + 1) / state[1];

    q( state, val, numerator, denominator );

    numerator = denominator + 1;
  }
}

//---------
// setup function : setup the state

FORCE_INLINE void setup ( double * state, double init = 0 ) 
{
  state[0] += init != 0 ? pow(init + 1.0/init, 1.0/3) : 3.0;
  state[1] += init != 0 ? pow(init + 1.0/init, 1.0/7) : 1.0/7;
}

//---------
// floppsyhash
// with 64 bit continued egyptian fractions

void floppsyhash_64 ( const void * key, int len,
                   uint32_t seed, void * out )
{
  const uint8_t * data = (const uint8_t *)key;
  uint8_t buf [16];
  double * state = (double*)buf;
  uint32_t * state32 = (uint32_t*)buf;
  double seed32 = (double)seed;

  uint8_t * seedbuf;
  seedbuf = (uint8_t *)&seed;

  setup( state, seed32 );
  round( seedbuf, 4, state );
  round( data, len, state );

  uint8_t output [8];
  uint32_t * h = (uint32_t*)output;
  
  h[0] = state32[0] + state32[3];
  h[1] = state32[1] + state32[2];

  ((uint32_t*)out)[0] = h[0];
  ((uint32_t*)out)[1] = h[1];
}