xref: /petsc/src/sys/classes/random/impls/rander48/rander48.c (revision 3cb3609b6a296a92a70bbd05421941ba494f28de)

#include <petsc/private/randomimpl.h>

typedef struct {
  unsigned short seed[3];
  unsigned short mult[3];
  unsigned short add;
} PetscRandom_Rander48;

#define RANDER48_SEED_0 (0x330e)
#define RANDER48_SEED_1 (0xabcd)
#define RANDER48_SEED_2 (0x1234)
#define RANDER48_MULT_0 (0xe66d)
#define RANDER48_MULT_1 (0xdeec)
#define RANDER48_MULT_2 (0x0005)
#define RANDER48_ADD    (0x000b)

static double _dorander48(PetscRandom_Rander48 *r48)
{
  unsigned long  accu;
  unsigned short temp[2];

  accu    = (unsigned long)r48->mult[0] * (unsigned long)r48->seed[0] + (unsigned long)r48->add;
  temp[0] = (unsigned short)accu; /* lower 16 bits */
  accu >>= sizeof(unsigned short) * 8;
  accu += (unsigned long)r48->mult[0] * (unsigned long)r48->seed[1] + (unsigned long)r48->mult[1] * (unsigned long)r48->seed[0];
  temp[1] = (unsigned short)accu; /* middle 16 bits */
  accu >>= sizeof(unsigned short) * 8;
  accu += (unsigned long)r48->mult[0] * r48->seed[2] + (unsigned long)r48->mult[1] * r48->seed[1] + (unsigned long)r48->mult[2] * r48->seed[0];
  r48->seed[0] = temp[0];
  r48->seed[1] = temp[1];
  r48->seed[2] = (unsigned short)accu;
  return ldexp((double)r48->seed[0], -48) + ldexp((double)r48->seed[1], -32) + ldexp((double)r48->seed[2], -16);
}

static PetscErrorCode PetscRandomSeed_Rander48(PetscRandom r)
{
  PetscRandom_Rander48 *r48 = (PetscRandom_Rander48 *)r->data;

  PetscFunctionBegin;
  r48->seed[0] = RANDER48_SEED_0;
  r48->seed[1] = (unsigned short)r->seed;
  r48->seed[2] = (unsigned short)(r->seed >> 16);
  r48->mult[0] = RANDER48_MULT_0;
  r48->mult[1] = RANDER48_MULT_1;
  r48->mult[2] = RANDER48_MULT_2;
  r48->add     = RANDER48_ADD;
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscRandomGetValue_Rander48(PetscRandom r, PetscScalar *val)
{
  PetscRandom_Rander48 *r48 = (PetscRandom_Rander48 *)r->data;

  PetscFunctionBegin;
#if defined(PETSC_USE_COMPLEX)
  if (r->iset) {
    *val = PetscRealPart(r->low) + PetscImaginaryPart(r->low) * PETSC_i;
    if (PetscRealPart(r->width)) *val += PetscRealPart(r->width) * _dorander48(r48);
    if (PetscImaginaryPart(r->width)) *val += PetscImaginaryPart(r->width) * _dorander48(r48) * PETSC_i;
  } else {
    *val = _dorander48(r48) + _dorander48(r48) * PETSC_i;
  }
#else
  if (r->iset) *val = r->width * _dorander48(r48) + r->low;
  else *val = _dorander48(r48);
#endif
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscRandomGetValueReal_Rander48(PetscRandom r, PetscReal *val)
{
  PetscRandom_Rander48 *r48 = (PetscRandom_Rander48 *)r->data;

  PetscFunctionBegin;
#if defined(PETSC_USE_COMPLEX)
  if (r->iset) *val = PetscRealPart(r->width) * _dorander48(r48) + PetscRealPart(r->low);
  else *val = _dorander48(r48);
#else
  if (r->iset) *val = r->width * _dorander48(r48) + r->low;
  else *val = _dorander48(r48);
#endif
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscRandomDestroy_Rander48(PetscRandom r)
{
  PetscFunctionBegin;
  PetscCall(PetscFree(r->data));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static struct _PetscRandomOps PetscRandomOps_Values = {
  PetscDesignatedInitializer(seed, PetscRandomSeed_Rander48),
  PetscDesignatedInitializer(getvalue, PetscRandomGetValue_Rander48),
  PetscDesignatedInitializer(getvaluereal, PetscRandomGetValueReal_Rander48),
  PetscDesignatedInitializer(getvalues, NULL),
  PetscDesignatedInitializer(getvaluesreal, NULL),
  PetscDesignatedInitializer(destroy, PetscRandomDestroy_Rander48),
  PetscDesignatedInitializer(setfromoptions, NULL),
};

/*MC
   PETSCRANDER48 - simple portable reimplementation of basic Unix `drand48()` random number generator that should generate the
        exact same random numbers on any system.

   Options Database Key:
. -random_type <rand,rand48,rander48,sprng> - select the random number generator at runtime

  Level: beginner

  Notes:
    This is the default random number generate provided by `PetscRandomCreate()` if you do not set a particular implementation.

  Each `PetscRandom` object created with this type has its own seed and its own history, so multiple `PetscRandom` objects of this type
  will not interfere with random numbers generated by other objects. Each PETSc object of this type will produce the exact same set of
  random numbers so if you wish different `PetscRandom` objects of this type set different seeds for each one after you create them with
  `PetscRandomSetSeed()` followed by `PetscRandomSeed()`.

.seealso: `PetscRandomCreate()`, `PetscRandomSetType()`, `PETSCRAND`, `PETSCRAND48`, `PETSCRANDER48`, `PETSCSPRNG`, `PetscRandomSetSeed()`,
          `PetscRandomSeed()`, `PetscRandomSetFromOptions()`
M*/

PETSC_EXTERN PetscErrorCode PetscRandomCreate_Rander48(PetscRandom r)
{
  PetscRandom_Rander48 *r48;

  PetscFunctionBegin;
  PetscCall(PetscNew(&r48));
  /* r48 does not need to be initialized because PetscRandomSeed() is always called before use and sets the needed values */
  r->data   = r48;
  r->ops[0] = PetscRandomOps_Values;
  PetscCall(PetscObjectChangeTypeName((PetscObject)r, PETSCRANDER48));
  PetscFunctionReturn(PETSC_SUCCESS);
}