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Overview
Comment:Comment changes only: Add several optimization marks in rowset.c. Add a header comment that explains what the various special comments mean.
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SHA1:8cdbe89ac6c22d632f677eb293111b3dbae7d6c1
User & Date: drh 2016-04-28 20:11:12
Context
2016-04-28
22:29
Further simplifications and improved commentting on the rowset.c module, including several optimization comments. check-in: 9f15a520 user: drh tags: trunk
20:11
Comment changes only: Add several optimization marks in rowset.c. Add a header comment that explains what the various special comments mean. check-in: 8cdbe89a user: drh tags: trunk
19:23
Fix typo in comment. No changes to code. check-in: 9f6f17b5 user: mistachkin tags: trunk
Changes
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Changes to src/rowset.c.

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** objected.
**
** In an OOM situation, the RowSet.db->mallocFailed flag is set and this
** routine returns NULL.
*/
static struct RowSetEntry *rowSetEntryAlloc(RowSet *p){
  assert( p!=0 );
  if( p->nFresh==0 ){


    struct RowSetChunk *pNew;
    pNew = sqlite3DbMallocRawNN(p->db, sizeof(*pNew));
    if( pNew==0 ){
      return 0;
    }
    pNew->pNextChunk = p->pChunk;
    p->pChunk = pNew;
................................................................................

  pEntry = rowSetEntryAlloc(p);
  if( pEntry==0 ) return;
  pEntry->v = rowid;
  pEntry->pRight = 0;
  pLast = p->pLast;
  if( pLast ){
    if( (p->rsFlags & ROWSET_SORTED)!=0 && rowid<=pLast->v ){


      p->rsFlags &= ~ROWSET_SORTED;
    }
    pLast->pRight = pEntry;
  }else{
    p->pEntry = pEntry;
  }
  p->pLast = pEntry;
................................................................................
*/
static struct RowSetEntry *rowSetNDeepTree(
  struct RowSetEntry **ppList,
  int iDepth
){
  struct RowSetEntry *p;         /* Root of the new tree */
  struct RowSetEntry *pLeft;     /* Left subtree */
  if( *ppList==0 ){

    return 0;
  }
  if( iDepth>1 ){   /*OPTIMIZATION-IF-TRUE*/
    /* This branch causes a *balanced* tree to be generated.  A valid tree
    ** is still generated without this branch, but it is wildly unbalanced
    ** and inefficient. */
    pLeft = rowSetNDeepTree(ppList, iDepth-1);
    p = *ppList;
    if( p==0 ){


      return pLeft;
    }
    p->pLeft = pLeft;
    *ppList = p->pRight;
    p->pRight = rowSetNDeepTree(ppList, iDepth-1);
  }else{
    p = *ppList;







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** objected.
**
** In an OOM situation, the RowSet.db->mallocFailed flag is set and this
** routine returns NULL.
*/
static struct RowSetEntry *rowSetEntryAlloc(RowSet *p){
  assert( p!=0 );
  if( p->nFresh==0 ){  /*OPTIMIZATION-IF-FALSE*/
    /* We could allocate a fresh RowSetEntry each time one is needed, but it
    ** is more efficient to pull a preallocated entry from the pool */
    struct RowSetChunk *pNew;
    pNew = sqlite3DbMallocRawNN(p->db, sizeof(*pNew));
    if( pNew==0 ){
      return 0;
    }
    pNew->pNextChunk = p->pChunk;
    p->pChunk = pNew;
................................................................................

  pEntry = rowSetEntryAlloc(p);
  if( pEntry==0 ) return;
  pEntry->v = rowid;
  pEntry->pRight = 0;
  pLast = p->pLast;
  if( pLast ){
    if( rowid<=pLast->v ){  /*OPTIMIZATION-IF-FALSE*/
      /* Avoid unnecessary sorts by preserving the ROWSET_SORTED flags
      ** where possible */
      p->rsFlags &= ~ROWSET_SORTED;
    }
    pLast->pRight = pEntry;
  }else{
    p->pEntry = pEntry;
  }
  p->pLast = pEntry;
................................................................................
*/
static struct RowSetEntry *rowSetNDeepTree(
  struct RowSetEntry **ppList,
  int iDepth
){
  struct RowSetEntry *p;         /* Root of the new tree */
  struct RowSetEntry *pLeft;     /* Left subtree */
  if( *ppList==0 ){ /*OPTIMIZATION-IF-TRUE*/
    /* Prevent unnecessary deep recursion when we run out of entries */
    return 0; 
  }
  if( iDepth>1 ){   /*OPTIMIZATION-IF-TRUE*/
    /* This branch causes a *balanced* tree to be generated.  A valid tree
    ** is still generated without this branch, but the tree is wildly
    ** unbalanced and inefficient. */
    pLeft = rowSetNDeepTree(ppList, iDepth-1);
    p = *ppList;
    if( p==0 ){     /*OPTIMIZATION-IF-FALSE*/
      /* It is safe to always return here, but the resulting tree
      ** would be unbalanced */
      return pLeft;
    }
    p->pLeft = pLeft;
    *ppList = p->pRight;
    p->pRight = rowSetNDeepTree(ppList, iDepth-1);
  }else{
    p = *ppList;

Changes to src/sqliteInt.h.

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**
*************************************************************************
** Internal interface definitions for SQLite.
**
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_




























/*
** Make sure that rand_s() is available on Windows systems with MSVC 2005
** or higher.
*/
#if defined(_MSC_VER) && _MSC_VER>=1400
#  define _CRT_RAND_S







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**
*************************************************************************
** Internal interface definitions for SQLite.
**
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/* Special Comments:
**
** Some comments have special meaning to the tools that measure test
** coverage:
**
**    NO_TEST                     - The branches on this line are not
**                                  measured by branch coverage.  This is
**                                  used on lines of code that actually
**                                  implement parts of coverage testing.
**
**    OPTIMIZATION-IF-TRUE        - This branch is allowed to alway be false
**                                  and the correct answer is still obtained,
**                                  though perhaps more slowly.
**
**    OPTIMIZATION-IF-FALSE       - This branch is allowed to alway be true
**                                  and the correct answer is still obtained,
**                                  though perhaps more slowly.
**
**    PREVENTS-HARMLESS-OVERREAD  - This branch prevents a buffer overread
**                                  that would be harmless and undetectable
**                                  if it did occur.  
**
** In all cases, the special comment must be enclosed in the usual
** slash-asterisk...asterisk-slash comment marks, with no spaces between the 
** asterisks and the comment text.
*/

/*
** Make sure that rand_s() is available on Windows systems with MSVC 2005
** or higher.
*/
#if defined(_MSC_VER) && _MSC_VER>=1400
#  define _CRT_RAND_S