SQLite

*/
struct fuzzer_stem {
  char *zBasis;              /* Word being fuzzed */
  int nBasis;                /* Length of the zBasis string */
  const fuzzer_rule *pRule;  /* Current rule to apply */
  int n;                     /* Apply pRule at this character offset */
  fuzzer_cost rBaseCost;     /* Base cost of getting to zBasis */
  fuzzer_cost rCostX;        /* Precomputed rBaseCost + pRule->rCost */
  fuzzer_stem *pNext;        /* Next stem in rCost order */
  fuzzer_stem *pHash;        /* Next stem with same hash on zBasis */
};

/* 
** A fuzzer virtual-table object 
*/
struct fuzzer_vtab {
  sqlite3_vtab base;         /* Base class - must be first */
  char *zClassName;          /* Name of this class.  Default: "fuzzer" */
  fuzzer_rule *pRule;        /* All active rules in this fuzzer */
  fuzzer_rule *pNewRule;     /* New rules to add when last cursor expires */
  int nCursor;               /* Number of active cursors */
};

#define FUZZER_HASH  4001    /* Hash table size */
#define FUZZER_NQUEUE  20    /* Number of slots on the stem queue */

/* A fuzzer cursor object */
struct fuzzer_cursor {
  sqlite3_vtab_cursor base;  /* Base class - must be first */
  sqlite3_int64 iRowid;      /* The rowid of the current word */
  fuzzer_vtab *pVtab;        /* The virtual table this cursor belongs to */
  fuzzer_cost rLimit;        /* Maximum cost of any term */
  fuzzer_stem *pStem;        /* Stem with smallest rCostX */
  fuzzer_stem *pDone;        /* Stems already processed to completion */
  fuzzer_stem *aQueue[FUZZER_NQUEUE];  /* Queue of stems with higher rCostX */
  int mxQueue;               /* Largest used index in aQueue[] */
  char *zBuf;                /* Temporary use buffer */
  int nBuf;                  /* Bytes allocated for zBuf */
  int nStem;                 /* Number of stems allocated */
  fuzzer_rule nullRule;      /* Null rule used first */
  fuzzer_stem *apHash[FUZZER_HASH]; /* Hash of previously generated terms */
};

/* Methods for the fuzzer module */
static int fuzzerConnect(
  sqlite3 *db,

      pX = fuzzerMergeRules(a[i], pX);
    }
    p->pRule = fuzzerMergeRules(p->pRule, pX);
  }
  p->nCursor++;
  return SQLITE_OK;
}

/*
** Free all stems in a list.
*/
static void fuzzerClearStemList(fuzzer_stem *pStem){
  while( pStem ){
    fuzzer_stem *pNext = pStem->pNext;
    sqlite3_free(pStem);
    pStem = pNext;
  }
}

/*
** Free up all the memory allocated by a cursor.  Set it rLimit to 0
** to indicate that it is at EOF.
*/
static void fuzzerClearCursor(fuzzer_cursor *pCur, int clearHash){
  int i;

  fuzzerClearStemList(pCur->pStem);
  fuzzerClearStemList(pCur->pDone);
  for(i=0; i<FUZZER_NQUEUE; i++) fuzzerClearStemList(pCur->aQueue[i]);
  pCur->rLimit = (fuzzer_cost)0;
  if( clearHash && pCur->nStem ){

    pCur->mxQueue = 0;
    pCur->pStem = 0;
    pCur->pDone = 0;
    memset(pCur->aQueue, 0, sizeof(pCur->aQueue));

    memset(pCur->apHash, 0, sizeof(pCur->apHash));
  }
  pCur->nStem = 0;
}

/*
** Close a fuzzer cursor.
*/
static int fuzzerClose(sqlite3_vtab_cursor *cur){
  fuzzer_cursor *pCur = (fuzzer_cursor *)cur;

  return h % FUZZER_HASH;
}

/*
** Current cost of a stem
*/
static fuzzer_cost fuzzerCost(fuzzer_stem *pStem){
  return pStem->rCostX = pStem->rBaseCost + pStem->pRule->rCost;
}

#if 0
/*
** Print a description of a fuzzer_stem on stderr.
*/
static void fuzzerStemPrint(

    );
  }else{
    char *zBuf = 0;
    int nBuf = 0;
    if( fuzzerRender(pStem, &zBuf, &nBuf)!=SQLITE_OK ) return;
    fprintf(stderr, "%s[%s](%d)-->{%s}(%d)%s",
      zPrefix,
      pStem->zBasis, pStem->rBaseCost, zBuf, pStem->,
      zSuffix
    );
    sqlite3_free(zBuf);
  }
}
#endif

      if( pRule->nFrom==0
       || memcmp(&pStem->zBasis[pStem->n], pRule->zFrom, pRule->nFrom)==0
      ){
        /* Found a rewrite case.  Make sure it is not a duplicate */
        int rc = fuzzerSeen(pCur, pStem);
        if( rc<0 ) return -1;
        if( rc==0 ){
          fuzzerCost(pStem);
          return 1;
        }
      }
    }
    pStem->n = -1;
    pStem->pRule = pRule->pNext;
    if( pStem->pRule && fuzzerCost(pStem)>pCur->rLimit ) pStem->pRule = 0;
  }
  return 0;
}

/*
** The two input stem lists are both sorted in order of increasing
** rCostX.  Merge them together into a single list, sorted by rCostX, and
** return a pointer to the head of that new list.
*/
static fuzzer_stem *fuzzerMergeStems(fuzzer_stem *pA, fuzzer_stem *pB){
  fuzzer_stem head;
  fuzzer_stem *pTail;

  pTail =  &head;
  while( pA && pB ){
    if( pA->rCostX<=pB->rCostX ){
      pTail->pNext = pA;
      pTail = pA;
      pA = pA->pNext;
    }else{
      pTail->pNext = pB;
      pTail = pB;
      pB = pB->pNext;
    }
  }
  if( pA==0 ){
    pTail->pNext = pB;
  }else{
    pTail->pNext = pA;
  }
  return head.pNext;
}

/*
** Load pCur->pStem with the lowest-cost stem.  Return a pointer
** to the lowest-cost stem.
*/
static fuzzer_stem *fuzzerLowestCostStem(fuzzer_cursor *pCur){
  fuzzer_stem *pBest, *pX;
  int iBest;
  int i;

  if( pCur->pStem==0 ){
    iBest = -1;
    pBest = 0;
    for(i=0; i<=pCur->mxQueue; i++){
      pX = pCur->aQueue[i];
      if( pX==0 ) continue;
      if( pBest==0 || pBest->rCostX>pX->rCostX ){
        pBest = pX;
        iBest = i;
      }
    } 
    if( pBest ){
      pCur->aQueue[iBest] = pBest->pNext;
      pBest->pNext = 0;
      pCur->pStem = pBest;
    }
  }
  return pCur->pStem;
}

/*
** Insert pNew into queue of pending stems.  Then find the stem
** with the lowest rCostX and move it into pCur->pStem.
** list.  The insert is done such the pNew is in the correct order
** according to fuzzer_stem.zBaseCost+fuzzer_stem.pRule->rCost.
*/
static fuzzer_stem *fuzzerInsert(fuzzer_cursor *pCur, fuzzer_stem *pNew){
  fuzzer_stem *pX;
  int i;

  /* If pCur->pStem exists and is greater than pNew, then make pNew
  ** the new pCur->pStem and insert the old pCur->pStem instead.
  */
  if( (pX = pCur->pStem)!=0 && pX->rCostX>pNew->rCostX ){
    pNew->pNext = 0;
    pCur->pStem = pNew;
    pNew = pX;
  }


  /* Insert the new value */
  pNew->pNext = 0;
  pX = pNew;
  for(i=0; i<=pCur->mxQueue; i++){
    if( pCur->aQueue[i] ){
      pX = fuzzerMergeStems(pX, pCur->aQueue[i]);
      pCur->aQueue[i] = 0;
    }else{

      pCur->aQueue[i] = pX;

      break;
    }
  }
  if( i>pCur->mxQueue ){
    if( i<FUZZER_NQUEUE ){
      pCur->mxQueue = i;
      pCur->aQueue[i] = pX;
    }else{
      assert( pCur->mxQueue==FUZZER_NQUEUE-1 );
      pX = fuzzerMergeStems(pX, pCur->aQueue[FUZZER_NQUEUE-1]);
      pCur->aQueue[FUZZER_NQUEUE-1] = pX;
    }
  }

  return fuzzerLowestCostStem(pCur);
}

/*
** Allocate a new fuzzer_stem.  Add it to the hash table but do not
** link it into either the pCur->pStem or pCur->pDone lists.
*/
static fuzzer_stem *fuzzerNewStem(

  if( pNew==0 ) return 0;
  memset(pNew, 0, sizeof(*pNew));
  pNew->zBasis = (char*)&pNew[1];
  pNew->nBasis = strlen(zWord);
  memcpy(pNew->zBasis, zWord, pNew->nBasis+1);
  pNew->pRule = pCur->pVtab->pRule;
  pNew->n = -1;
  pNew->rBaseCost = pNew->rCostX = rBaseCost;
  h = fuzzerHash(pNew->zBasis);
  pNew->pHash = pCur->apHash[h];
  pCur->apHash[h] = pNew;
  pCur->nStem++;
  return pNew;
}


/*
** Advance a cursor to its next row of output
*/
static int fuzzerNext(sqlite3_vtab_cursor *cur){
  fuzzer_cursor *pCur = (fuzzer_cursor*)cur;
  int rc;
  fuzzer_stem *pStem, *pNew;

  pCur->iRowid++;

  /* Use the element the cursor is currently point to to create
  ** a new stem and insert the new stem into the priority queue.
  */
  pStem = pCur->pStem;
  if( pStem->rCostX>0 ){
    rc = fuzzerRender(pStem, &pCur->zBuf, &pCur->nBuf);
    if( rc==SQLITE_NOMEM ) return SQLITE_NOMEM;
    pNew = fuzzerNewStem(pCur, pCur->zBuf, pStem->rCostX);
    if( pNew ){
      if( fuzzerAdvance(pCur, pNew)==0 ){
        pNew->pNext = pCur->pDone;
        pCur->pDone = pNew;
      }else{
        if( fuzzerInsert(pCur, pNew)==pNew ){

          return SQLITE_OK;
        }
      }
    }else{
      return SQLITE_NOMEM;
    }
  }

  /* Adjust the priority queue so that the first element of the
  ** stem list is the next lowest cost word.
  */
  while( (pStem = pCur->pStem)!=0 ){
    if( fuzzerAdvance(pCur, pStem) ){
      pCur->pStem = 0;
      pStem = fuzzerInsert(pCur, pStem);
      if( (rc = fuzzerSeen(pCur, pStem))!=0 ){
        if( rc<0 ) return SQLITE_NOMEM;
        continue;
      }
      return SQLITE_OK;  /* New word found */
    }
    pCur->pStem = 0;
    pStem->pNext = pCur->pDone;
    pCur->pDone = pStem;
    if( fuzzerLowestCostStem(pCur) ){
      rc = fuzzerSeen(pCur, pCur->pStem);
      if( rc<0 ) return SQLITE_NOMEM;
      if( rc==0 ){
        return SQLITE_OK;
      }
    }
  }

    /* the "word" column */
    if( fuzzerRender(pCur->pStem, &pCur->zBuf, &pCur->nBuf)==SQLITE_NOMEM ){
      return SQLITE_NOMEM;
    }
    sqlite3_result_text(ctx, pCur->zBuf, -1, SQLITE_TRANSIENT);
  }else if( i==1 ){
    /* the "distance" column */
    sqlite3_result_int(ctx, pCur->pStem->rCostX);
  }else{
    /* All other columns are NULL */
    sqlite3_result_null(ctx);
  }
  return SQLITE_OK;
}