/*

 *

 *  Copyright (C) 2021-2025, OFFIS e.V.

 *  All rights reserved.  See COPYRIGHT file for details.

 *

 *  This software and supporting documentation were developed by

 *

 *    OFFIS e.V.

 *    R&D Division Health

 *    Escherweg 2

 *    D-26121 Oldenburg, Germany

 *

 *

 *  Module:  ofstd

 *

 *  Author:  Marco Eichelberg, based on the reference implementation

 *   of the ISAAC PRNG by Bob Jenkins (Public Domain).

 *

 *  Purpose: Cryptographically secure PRNG based on Bob Jenkins's ISAAC algorithm

 *

 */

#include "dcmtk/config/osconfig.h"

#include "dcmtk/ofstd/ofrand.h"

#include "dcmtk/ofstd/ofcast.h"

#include "dcmtk/ofstd/ofstd.h"

#include "dcmtk/ofstd/ofstdinc.h"

#include <ctime>

BEGIN_EXTERN_C

#ifdef HAVE_SYS_TIME_H

#include <sys/time.h>

#endif

END_EXTERN_C

#ifdef HAVE_WINDOWS_H

#define WIN32_LEAN_AND_MEAN

#include <windows.h>

#endif

#define ind(mm,x)  ((mm)[(x>>2)&(OFRandom_SIZ-1)])

#define rngstep(mix,a,b,mm,m,m2,r,x) \

{ \

  x = *m;  \

  a = ((a^(mix)) + *(m2++)); \

  *(m++) = y = (ind(mm,x) + a + b); \

  *(r++) = b = (ind(mm,y>>OFRandom_SIZL) + x) & 0xffffffff; \

}

#define mix(a,b,c,d,e,f,g,h) \

{ \

   a^=b<<11;              d+=a; b+=c; \

   b^=(c&0xffffffff)>>2;  e+=b; c+=d; \

   c^=d<<8;               f+=c; d+=e; \

   d^=(e&0xffffffff)>>16; g+=d; e+=f; \

   e^=f<<10;              h+=e; f+=g; \

   f^=(g&0xffffffff)>>4;  a+=f; g+=h; \

   g^=h<<8;               b+=g; h+=a; \

   h^=(a&0xffffffff)>>9;  c+=h; a+=b; \

}

OFRandom::OFRandom()

: randcnt(OFRandom_SIZ)

, randrsl()

, randmem()

, randa(0)

, randb(0)

, randc(0)

{

   /* initialize randrsl based on the current time, CPU clock count, and process ID */

   Uint32 tm = OFstatic_cast(Uint32, time(NULL));

   Uint32 cl = OFstatic_cast(Uint32, clock());

   Uint32 pi = OFstatic_cast(Uint32, OFStandard::getProcessID());

#ifdef _WIN32

    ULARGE_INTEGER wintm;

    /* tm is number of 100ns ticks since Jan 01 1601.

     * We only use the lowest 32 bits of this number.

     */

    GetSystemTimeAsFileTime(OFreinterpret_cast(FILETIME *, &wintm));

    Uint32 tm2 = OFstatic_cast(Uint32, wintm.LowPart);

#else

    struct timeval posixtm;

    gettimeofday(&posixtm, NULL);

    /* sub-second part of current time in microseconds */

    Uint32 tm2 = OFstatic_cast(Uint32, posixtm.tv_usec);

#endif

   for (int i=0; i<OFRandom_SIZ; i += 4)  // OFRandom_SIZ is dividable by 4

   {

     randrsl[i] = tm++;

     randrsl[i+1] = cl++;

     randrsl[i+2] = pi++;

     randrsl[i+3] = tm2++;

   }

   mixSeed();

}

void OFRandom::mixSeed()

{

   int i;

   Uint32 a,b,c,d,e,f,g,h;

   a=b=c=d=e=f=g=h=0x9e3779b9;  /* the golden ratio */

   for (i=0; i<4; ++i) /* scramble it */

   {

     mix(a,b,c,d,e,f,g,h);

   }

   /* initialize using the contents of randrsl[] as the seed */

   for (i=0; i<OFRandom_SIZ; i+=8)

   {

     a+=randrsl[i  ]; b+=randrsl[i+1];

     c+=randrsl[i+2]; d+=randrsl[i+3];

     e+=randrsl[i+4]; f+=randrsl[i+5];

     g+=randrsl[i+6]; h+=randrsl[i+7];

     mix(a,b,c,d,e,f,g,h);

     randmem[i  ]=a; randmem[i+1]=b; randmem[i+2]=c; randmem[i+3]=d;

     randmem[i+4]=e; randmem[i+5]=f; randmem[i+6]=g; randmem[i+7]=h;

   }

   /* do a second pass to make all of the seed affect all of m */

   for (i=0; i<OFRandom_SIZ; i+=8)

   {

     a+=randmem[i  ]; b+=randmem[i+1];

     c+=randmem[i+2]; d+=randmem[i+3];

     e+=randmem[i+4]; f+=randmem[i+5];

     g+=randmem[i+6]; h+=randmem[i+7];

     mix(a,b,c,d,e,f,g,h);

     randmem[i  ]=a; randmem[i+1]=b; randmem[i+2]=c; randmem[i+3]=d;

     randmem[i+4]=e; randmem[i+5]=f; randmem[i+6]=g; randmem[i+7]=h;

   }

   isaac(); /* fill in the first set of results */}

void OFRandom::seed(Uint32 sval)

{

   for (int i=0; i<OFRandom_SIZ; i++)

   {

     randrsl[i] = sval;

   }

   randa = 0;

   randb = 0;

   randc = 0;

   mixSeed();

}

void OFRandom::isaac()

{

   Uint32 x,y,*m,*m2,*mend;

   Uint32 *r = randrsl;

   Uint32 a = randa;

   Uint32 b = randb + (++randc);

   for (m = randmem, mend = m2 = m+(OFRandom_SIZ/2); m<mend; )

   {

      rngstep( a<<13, a, b, randmem, m, m2, r, x);

      rngstep( (a & 0xffffffff) >>6 , a, b, randmem, m, m2, r, x);

      rngstep( a<<2 , a, b, randmem, m, m2, r, x);

      rngstep( (a & 0xffffffff) >>16, a, b, randmem, m, m2, r, x);

   }

   for (m2 = randmem; m2<mend; )

   {

      rngstep( a<<13, a, b, randmem, m, m2, r, x);

      rngstep( (a & 0xffffffff) >>6 , a, b, randmem, m, m2, r, x);

      rngstep( a<<2 , a, b, randmem, m, m2, r, x);

      rngstep( (a & 0xffffffff) >>16, a, b, randmem, m, m2, r, x);

   }

   randb = b; randa = a;

   randcnt = OFRandom_SIZ;

}

Uint32 OFRandom::getRND32()

{

  // check if we still have random numbers left

  if (randcnt == 0) isaac();

  // we use the random numbers from last to first

  return randrsl[--randcnt];

}

Uint16 OFRandom::getRND16()

{

  // use one 32-bit random number and ignore the extra bits

  return OFstatic_cast(Uint16, getRND32());

}

Uint8 OFRandom::getRND8()

{

  // use one 32-bit random number and ignore the extra bits

  return OFstatic_cast(Uint8, getRND32());

}

Uint64 OFRandom::getRND64()

{

  // get a 32-bit random number

  Uint64 result = getRND32();

  // shift into upper 32 bits of the 64-bit word

  result <<= 32;

  // get a second 32-bit random number

  result |= getRND32();

  return result;

}