xref: /petsc/src/sys/classes/random/impls/random123/random123.c (revision dc085601c640b1ee893c6d93111e4696da56d24d)

#include <petsc/private/randomimpl.h>
#include <Random123/threefry.h>

/* The structure of the Random123 methods are similar enough that templates could be used to make the other CBRNGs in
 * the package (aes, ars, philox) available, as well as different block sizes.  But threefry4x64 is a good default,
 * and I'd rather get a simple implementation up and working and come back if there's interest. */
typedef struct _n_PetscRandom123 {
  threefry4x64_ctr_t counter;
  threefry4x64_key_t key;
  threefry4x64_ctr_t result;
  PetscInt           count;
} PetscRandom123;

R123_ULONG_LONG PETSCR123_SEED_0 = R123_64BIT(0x615D333D2655FE14);
R123_ULONG_LONG PETSCR123_SEED_1 = R123_64BIT(0xAFF6369B3EE9FE96);
R123_ULONG_LONG PETSCR123_SEED_2 = R123_64BIT(0x5956EBC717B60E07);
R123_ULONG_LONG PETSCR123_SEED_3 = R123_64BIT(0xEE8612A0CBEABFF1);

static PetscErrorCode PetscRandomSeed_Random123(PetscRandom r)
{
  threefry4x64_ukey_t ukey;
  PetscRandom123     *r123 = (PetscRandom123 *)r->data;

  PetscFunctionBegin;
  ukey.v[0] = (R123_ULONG_LONG)r->seed;
  ukey.v[1] = PETSCR123_SEED_1;
  ukey.v[2] = PETSCR123_SEED_2;
  ukey.v[3] = PETSCR123_SEED_3;
  /* The point of seeding should be that every time the sequence is seeded you get the same output.  In this CBRNG,
   * that means we have to initialize the key and reset the counts */
  r123->key          = threefry4x64keyinit(ukey);
  r123->counter.v[0] = 0;
  r123->counter.v[1] = 1;
  r123->counter.v[2] = 2;
  r123->counter.v[3] = 3;
  r123->result       = threefry4x64(r123->counter, r123->key);
  r123->count        = 0;
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscReal PetscRandom123Step(PetscRandom123 *r123)
{
  PetscReal scale = 1. / ((PetscReal)UINT64_MAX + 1.);
  PetscReal shift = .5 * scale;
  PetscInt  mod   = (r123->count++) % 4;
  PetscReal ret;

  ret = r123->result.v[mod] * scale + shift;

  if (mod == 3) {
    r123->counter.v[0] += 4;
    r123->counter.v[1] += 4;
    r123->counter.v[2] += 4;
    r123->counter.v[3] += 4;
    r123->result = threefry4x64(r123->counter, r123->key);
  }

  return ret;
}

static PetscErrorCode PetscRandomGetValue_Random123(PetscRandom r, PetscScalar *val)
{
  PetscRandom123 *r123 = (PetscRandom123 *)r->data;
  PetscScalar     rscal;

  PetscFunctionBegin;
#if defined(PETSC_USE_COMPLEX)
  {
    PetscReal re = PetscRandom123Step(r123);
    PetscReal im = PetscRandom123Step(r123);

    if (r->iset) {
      re = re * PetscRealPart(r->width) + PetscRealPart(r->low);
      im = im * PetscImaginaryPart(r->width) + PetscImaginaryPart(r->low);
    }

    rscal = PetscCMPLX(re, im);
  }
#else
  rscal = PetscRandom123Step(r123);
  if (r->iset) rscal = rscal * r->width + r->low;
#endif
  *val = rscal;
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscRandomGetValueReal_Random123(PetscRandom r, PetscReal *val)
{
  PetscRandom123 *r123 = (PetscRandom123 *)r->data;
  PetscReal       rreal;

  PetscFunctionBegin;
  rreal = PetscRandom123Step(r123);
  if (r->iset) rreal = rreal * PetscRealPart(r->width) + PetscRealPart(r->low);
  *val = rreal;
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscRandomGetValuesReal_Random123(PetscRandom r, PetscInt n, PetscReal vals[])
{
  PetscRandom123 *r123 = (PetscRandom123 *)r->data;
  PetscInt        peel_start;
  PetscInt        rem, lim;
  PetscReal       scale = 1. / ((PetscReal)UINT64_MAX + 1.);
  PetscReal       shift = .5 * scale;
  PetscRandom123  r123_copy;

  PetscFunctionBegin;
  peel_start = (4 - (r123->count % 4)) % 4;
  peel_start = PetscMin(n, peel_start);
  for (PetscInt i = 0; i < peel_start; i++) PetscCall(PetscRandomGetValueReal(r, &vals[i]));
  PetscAssert((r123->count % 4) == 0, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Bad modular arithmetic");
  n -= peel_start;
  vals += peel_start;
  rem = (n % 4);
  lim = n - rem;
  if (r->iset) {
    scale *= PetscRealPart(r->width);
    shift *= PetscRealPart(r->width);
    shift += PetscRealPart(r->low);
  }
  r123_copy = *r123;
  for (PetscInt i = 0; i < lim; i += 4, vals += 4) {
    vals[0] = r123_copy.result.v[0] * scale + shift;
    vals[1] = r123_copy.result.v[1] * scale + shift;
    vals[2] = r123_copy.result.v[2] * scale + shift;
    vals[3] = r123_copy.result.v[3] * scale + shift;
    r123_copy.counter.v[0] += 4;
    r123_copy.counter.v[1] += 4;
    r123_copy.counter.v[2] += 4;
    r123_copy.counter.v[3] += 4;
    r123_copy.result = threefry4x64(r123->counter, r123->key);
  }
  r123_copy.count += lim;
  *r123 = r123_copy;
  for (PetscInt i = 0; i < rem; i++) PetscCall(PetscRandomGetValueReal(r, &vals[i]));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscRandomGetValues_Random123(PetscRandom r, PetscInt n, PetscScalar vals[])
{
  PetscFunctionBegin;
#if PetscDefined(USE_COMPLEX)
  for (PetscInt i = 0; i < n; i++) PetscCall(PetscRandomGetValue_Random123(r, n, &vals[i]));
#else
  PetscCall(PetscRandomGetValuesReal_Random123(r, n, vals));
#endif
  PetscFunctionReturn(PETSC_SUCCESS);
}

static PetscErrorCode PetscRandomDestroy_Random123(PetscRandom r)
{
  PetscFunctionBegin;
  PetscCall(PetscFree(r->data));
  PetscFunctionReturn(PETSC_SUCCESS);
}

static struct _PetscRandomOps PetscRandomOps_Values = {
  // clang-format off
  PetscDesignatedInitializer(seed, PetscRandomSeed_Random123),
  PetscDesignatedInitializer(getvalue, PetscRandomGetValue_Random123),
  PetscDesignatedInitializer(getvaluereal, PetscRandomGetValueReal_Random123),
  PetscDesignatedInitializer(getvalues, PetscRandomGetValues_Random123),
  PetscDesignatedInitializer(getvaluesreal, PetscRandomGetValuesReal_Random123),
  PetscDesignatedInitializer(destroy, PetscRandomDestroy_Random123),
  // clang-format on
};

/*MC
   PETSCRANDOM123 - access to Random123 counter based pseudorandom number generators (currently threefry4x64)

   Options Database Key:
. -random_type <rand,rand48,sprng,random123> - select the random number generator at runtim

  Level: beginner

  Note:
   PETSc must be ./configure with the option --download-random123 to use this random number generator.

.seealso: `RandomCreate()`, `RandomSetType()`, `PETSCRAND`, `PETSCRAND48`, `PETSCSPRNG`, `PetscRandomSetFromOptions()`
M*/

PETSC_EXTERN PetscErrorCode PetscRandomCreate_Random123(PetscRandom r)
{
  PetscRandom123 *r123;

  PetscFunctionBegin;
  PetscCall(PetscNew(&r123));
  r->data   = r123;
  r->ops[0] = PetscRandomOps_Values;
  PetscCall(PetscObjectChangeTypeName((PetscObject)r, PETSCRANDOM123));
  PetscCall(PetscRandomSeed(r));
  PetscFunctionReturn(PETSC_SUCCESS);
}