SQLite

/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is responsible for
** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.307 2008/05/30 14:58:37 drh Exp $
*/
#include "sqliteInt.h"

/*
** The number of bits in a Bitmask.  "BMS" means "BitMask Size".
*/
#define BMS  (sizeof(Bitmask)*8)

** Add a new entries to the WhereClause structure.  Increase the allocated
** space as necessary.
**
** If the flags argument includes TERM_DYNAMIC, then responsibility
** for freeing the expression p is assumed by the WhereClause object.
**
** WARNING:  This routine might reallocate the space used to store
** WhereTerms.  All pointers to WhereTerms should be invalidated after
** calling this routine.  Such pointers may be reinitialized by referencing
** the pWC->a[] array.
*/
static int whereClauseInsert(WhereClause *pWC, Expr *p, int flags){
  WhereTerm *pTerm;
  int idx;
  if( pWC->nTerm>=pWC->nSlot ){

/*
** Swap two objects of type T.
*/
#define SWAP(TYPE,A,B) {TYPE t=A; A=B; B=t;}

/*
** Commute a comparison operator.  Expressions of the form "X op Y"
** are converted into "Y op X".
**
** If a collation sequence is associated with either the left or right
** side of the comparison, it remains associated with the same side after
** the commutation. So "Y collate NOCASE op X" becomes 
** "X collate NOCASE op Y". This is because any collation sequence on
** the left hand side of a comparison overrides any collation sequence 

**
** The context is that we have multiple OR-connected equality terms
** like this:
**
**           a=<expr1> OR  a=<expr2> OR b=<expr3>  OR ...
**
** The pOrTerm input to this routine corresponds to a single term of
** this OR clause.  In order for the term to be a candidate for
** conversion to an IN operator, the following must be true:
**
**     *  The left-hand side of the term must be the column which
**        is identified by iCursor and iColumn.
**
**     *  If the right-hand side is also a column, then the affinities
**        of both right and left sides must be such that no type

**
** Since the last two terms are duplicates, only one of them
** has to qualify in order for the whole phrase to qualify.  When
** this routine is called, we know that pOrTerm did not qualify.
** This routine merely checks to see if pOrTerm has a duplicate that
** might qualify.  If there is a duplicate that has not yet been
** disqualified, then return true.  If there are no duplicates, or
** the duplicate has also been disqualified, return false.
*/
static int orTermHasOkDuplicate(WhereClause *pOr, WhereTerm *pOrTerm){
  if( pOrTerm->flags & TERM_COPIED ){
    /* This is the original term.  The duplicate is to the left had
    ** has not yet been analyzed and thus has not yet been disqualified. */
    return 1;
  }

  }
  return 0;
}

/*
** Prepare a crude estimate of the logarithm of the input value.
** The results need not be exact.  This is only used for estimating
** the total cost of performing operations with O(logN) or O(NlogN)
** complexity.  Because N is just a guess, it is no great tragedy if
** logN is a little off.
*/
static double estLog(double N){
  double logN = 1;
  double x = 10;
  while( N>x ){