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

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

 14: R123_ULONG_LONG PETSCR123_SEED_0 = R123_64BIT(0x615D333D2655FE14);
 15: R123_ULONG_LONG PETSCR123_SEED_1 = R123_64BIT(0xAFF6369B3EE9FE96);
 16: R123_ULONG_LONG PETSCR123_SEED_2 = R123_64BIT(0x5956EBC717B60E07);
 17: R123_ULONG_LONG PETSCR123_SEED_3 = R123_64BIT(0xEE8612A0CBEABFF1);

 19: static PetscErrorCode PetscRandomSeed_Random123(PetscRandom r)
 20: {
 21:   threefry4x64_ukey_t ukey;
 22:   PetscRandom123     *r123 = (PetscRandom123 *)r->data;

 24:   PetscFunctionBegin;
 25:   ukey.v[0] = (R123_ULONG_LONG)r->seed;
 26:   ukey.v[1] = PETSCR123_SEED_1;
 27:   ukey.v[2] = PETSCR123_SEED_2;
 28:   ukey.v[3] = PETSCR123_SEED_3;
 29:   /* The point of seeding should be that every time the sequence is seeded you get the same output.  In this CBRNG,
 30:    * that means we have to initialize the key and reset the counts */
 31:   r123->key          = threefry4x64keyinit(ukey);
 32:   r123->counter.v[0] = 0;
 33:   r123->counter.v[1] = 1;
 34:   r123->counter.v[2] = 2;
 35:   r123->counter.v[3] = 3;
 36:   r123->result       = threefry4x64(r123->counter, r123->key);
 37:   r123->count        = 0;
 38:   PetscFunctionReturn(PETSC_SUCCESS);
 39: }

 41: static PetscReal PetscRandom123Step(PetscRandom123 *r123)
 42: {
 43:   PetscReal scale = ((PetscReal)1.) / (((PetscReal)UINT64_MAX) + ((PetscReal)1.));
 44:   PetscReal shift = .5 * scale;
 45:   PetscInt  mod   = (r123->count++) % 4;
 46:   PetscReal ret;

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

 50:   if (mod == 3) {
 51:     r123->counter.v[0] += 4;
 52:     r123->counter.v[1] += 4;
 53:     r123->counter.v[2] += 4;
 54:     r123->counter.v[3] += 4;
 55:     r123->result = threefry4x64(r123->counter, r123->key);
 56:   }

 58:   return ret;
 59: }

 61: static PetscErrorCode PetscRandomGetValue_Random123(PetscRandom r, PetscScalar *val)
 62: {
 63:   PetscRandom123 *r123 = (PetscRandom123 *)r->data;
 64:   PetscScalar     rscal;

 66:   PetscFunctionBegin;
 67: #if defined(PETSC_USE_COMPLEX)
 68:   {
 69:     PetscReal re = PetscRandom123Step(r123);
 70:     PetscReal im = PetscRandom123Step(r123);

 72:     if (r->iset) {
 73:       re = re * PetscRealPart(r->width) + PetscRealPart(r->low);
 74:       im = im * PetscImaginaryPart(r->width) + PetscImaginaryPart(r->low);
 75:     }

 77:     rscal = PetscCMPLX(re, im);
 78:   }
 79: #else
 80:   rscal = PetscRandom123Step(r123);
 81:   if (r->iset) rscal = rscal * r->width + r->low;
 82: #endif
 83:   *val = rscal;
 84:   PetscFunctionReturn(PETSC_SUCCESS);
 85: }

 87: static PetscErrorCode PetscRandomGetValueReal_Random123(PetscRandom r, PetscReal *val)
 88: {
 89:   PetscRandom123 *r123 = (PetscRandom123 *)r->data;
 90:   PetscReal       rreal;

 92:   PetscFunctionBegin;
 93:   rreal = PetscRandom123Step(r123);
 94:   if (r->iset) rreal = rreal * PetscRealPart(r->width) + PetscRealPart(r->low);
 95:   *val = rreal;
 96:   PetscFunctionReturn(PETSC_SUCCESS);
 97: }

 99: static PetscErrorCode PetscRandomDestroy_Random123(PetscRandom r)
100: {
101:   PetscFunctionBegin;
102:   PetscCall(PetscFree(r->data));
103:   PetscFunctionReturn(PETSC_SUCCESS);
104: }

106: static struct _PetscRandomOps PetscRandomOps_Values = {
107:   PetscDesignatedInitializer(seed, PetscRandomSeed_Random123),
108:   PetscDesignatedInitializer(getvalue, PetscRandomGetValue_Random123),
109:   PetscDesignatedInitializer(getvaluereal, PetscRandomGetValueReal_Random123),
110:   PetscDesignatedInitializer(getvalues, NULL),
111:   PetscDesignatedInitializer(getvaluesreal, NULL),
112:   PetscDesignatedInitializer(destroy, PetscRandomDestroy_Random123),
113: };

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

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

121:   Level: beginner

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

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

129: PETSC_EXTERN PetscErrorCode PetscRandomCreate_Random123(PetscRandom r)
130: {
131:   PetscRandom123 *r123;

133:   PetscFunctionBegin;
134:   PetscCall(PetscNew(&r123));
135:   r->data   = r123;
136:   r->ops[0] = PetscRandomOps_Values;
137:   PetscCall(PetscObjectChangeTypeName((PetscObject)r, PETSCRANDOM123));
138:   PetscCall(PetscRandomSeed(r));
139:   PetscFunctionReturn(PETSC_SUCCESS);
140: }