Actual source code: random123.c

petsc-master 2019-08-19
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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: }