Date: 2021-03-03T22:25:39+00:00

Actual source code: random123.c
petsc-3.14.5 2021-03-03
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      1: #include <../src/sys/classes/random/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: {
      9:   threefry4x64_ctr_t  counter;
     10:   threefry4x64_key_t  key;
     11:   threefry4x64_ctr_t  result;
     12:   PetscInt            count;
     13: }
     14: PetscRandom123;

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

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

     27:   ukey.v[0] = (R123_ULONG_LONG) r->seed;
     28:   ukey.v[1] = PETSCR123_SEED_1;
     29:   ukey.v[2] = PETSCR123_SEED_2;
     30:   ukey.v[3] = PETSCR123_SEED_3;
     31:   /* The point of seeding should be that every time the sequence is seeded you get the same output.  In this CBRNG,
     32:    * that means we have to initialize the key and reset the counts */
     33:   r123->key = threefry4x64keyinit(ukey);
     34:   r123->counter.v[0] = 0;
     35:   r123->counter.v[1] = 1;
     36:   r123->counter.v[2] = 2;
     37:   r123->counter.v[3] = 3;
     38:   r123->result = threefry4x64(r123->counter,r123->key);
     39:   r123->count = 0;
     40:   return(0);
     41: }

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

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

     52:   if (mod == 3) {
     53:     r123->counter.v[0] += 4;
     54:     r123->counter.v[1] += 4;
     55:     r123->counter.v[2] += 4;
     56:     r123->counter.v[3] += 4;
     57:     r123->result = threefry4x64(r123->counter,r123->key);
     58:   }

     60:   return ret;
     61: }

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

     69: #if defined(PETSC_USE_COMPLEX)
     70:   {
     71:     PetscReal re = PetscRandom123Step(r123);
     72:     PetscReal im = PetscRandom123Step(r123);

     74:     if (r->iset) {
     75:       re = re * PetscRealPart(r->width) + PetscRealPart(r->low);
     76:       im = im * PetscImaginaryPart(r->width) + PetscImaginaryPart(r->low);
     77:     }

     79:     rscal = PetscCMPLX(re,im);
     80:   }
     81: #else
     82:   rscal = PetscRandom123Step(r123);
     83:   if (r->iset) rscal = rscal * r->width + r->low;
     84: #endif
     85:   *val = rscal;
     86:   return(0);
     87: }

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

     95:   rreal = PetscRandom123Step(r123);
     96:   if (r->iset) rreal = rreal * PetscRealPart(r->width) + PetscRealPart(r->low);
     97:   *val = rreal;
     98:   return(0);
     99: }

    101: PetscErrorCode PetscRandomDestroy_Random123(PetscRandom r)
    102: {

    106:   PetscFree(r->data);
    107:   return(0);
    108: }

    110: static struct _PetscRandomOps PetscRandomOps_Values = {
    111:   /* 0 */
    112:   PetscRandomSeed_Random123,
    113:   PetscRandomGetValue_Random123,
    114:   PetscRandomGetValueReal_Random123,
    115:   PetscRandomDestroy_Random123,
    116:   /* 5 */
    117:   0
    118: };

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

    123:    Options Database Keys:
    124: . -random_type <rand,rand48,sprng,random123>

    126:   Level: beginner

    128:    PETSc must have been ./configure with the option --download-random123 to use
    129:    this random number generator.

    131: .seealso: RandomCreate(), RandomSetType(), PETSCRAND, PETSCRAND48, PETSCSPRNG
    132: M*/

    134: PETSC_EXTERN PetscErrorCode PetscRandomCreate_Random123(PetscRandom r)
    135: {
    136:   PetscRandom123 *r123;

    140:   PetscNewLog(r,&r123);
    141:   r->data = r123;
    142:   PetscMemcpy(r->ops,&PetscRandomOps_Values,sizeof(PetscRandomOps_Values));
    143:   PetscObjectChangeTypeName((PetscObject)r,PETSCRANDOM123);
    144:   PetscRandomSeed(r);
    145:   return(0);
    146: }