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Overview
Comment:Change the OP_IfNotZero opcode so that it decrements register P1 by 1 rather than the value in P3, and so that it only decrements if originally positive. This avoids decrementing the smallest 64-bit signed integer.
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SHA1:165c044686212fbf7182dd560ad1e57eb4cc9838
User & Date: drh 2016-12-18 17:42:00
Context
2016-12-21
19:45
Simplifications to the way UnpackedRecord objects are allocated. Smaller and faster code that also fixes a subtle (currently unreachable) bug. check-in: f7ab01f2 user: drh tags: trunk
2016-12-18
17:42
Change the OP_IfNotZero opcode so that it decrements register P1 by 1 rather than the value in P3, and so that it only decrements if originally positive. This avoids decrementing the smallest 64-bit signed integer. check-in: 165c0446 user: drh tags: trunk
2016-12-17
21:07
Refinements to the new dbfuzz test program. check-in: 50325abe user: drh tags: trunk
Changes
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Changes to src/select.c.

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  if( iLimit ){
    int addr;
    int r1 = 0;
    /* Fill the sorter until it contains LIMIT+OFFSET entries.  (The iLimit
    ** register is initialized with value of LIMIT+OFFSET.)  After the sorter
    ** fills up, delete the least entry in the sorter after each insert.
    ** Thus we never hold more than the LIMIT+OFFSET rows in memory at once */
    addr = sqlite3VdbeAddOp3(v, OP_IfNotZero, iLimit, 0, 1); VdbeCoverage(v);
    sqlite3VdbeAddOp1(v, OP_Last, pSort->iECursor);
    if( pSort->bOrderedInnerLoop ){
      r1 = ++pParse->nMem;
      sqlite3VdbeAddOp3(v, OP_Column, pSort->iECursor, nExpr, r1);
      VdbeComment((v, "seq"));
    }
    sqlite3VdbeAddOp1(v, OP_Delete, pSort->iECursor);







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  if( iLimit ){
    int addr;
    int r1 = 0;
    /* Fill the sorter until it contains LIMIT+OFFSET entries.  (The iLimit
    ** register is initialized with value of LIMIT+OFFSET.)  After the sorter
    ** fills up, delete the least entry in the sorter after each insert.
    ** Thus we never hold more than the LIMIT+OFFSET rows in memory at once */
    addr = sqlite3VdbeAddOp1(v, OP_IfNotZero, iLimit); VdbeCoverage(v);
    sqlite3VdbeAddOp1(v, OP_Last, pSort->iECursor);
    if( pSort->bOrderedInnerLoop ){
      r1 = ++pParse->nMem;
      sqlite3VdbeAddOp3(v, OP_Column, pSort->iECursor, nExpr, r1);
      VdbeComment((v, "seq"));
    }
    sqlite3VdbeAddOp1(v, OP_Delete, pSort->iECursor);

Changes to src/vdbe.c.

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    pOut->u.i = -1;
  }else{
    pOut->u.i = x;
  }
  break;
}

/* Opcode: IfNotZero P1 P2 P3 * *
** Synopsis: if r[P1]!=0 then r[P1]-=P3, goto P2
**
** Register P1 must contain an integer.  If the content of register P1 is
** initially nonzero, then subtract P3 from the value in register P1 and

** jump to P2.  If register P1 is initially zero, leave it unchanged
** and fall through.
*/
case OP_IfNotZero: {        /* jump, in1 */
  pIn1 = &aMem[pOp->p1];
  assert( pIn1->flags&MEM_Int );
  VdbeBranchTaken(pIn1->u.i<0, 2);
  if( pIn1->u.i ){
     pIn1->u.i -= pOp->p3;
     goto jump_to_p2;
  }
  break;
}

/* Opcode: DecrJumpZero P1 P2 * * *
** Synopsis: if (--r[P1])==0 goto P2







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    pOut->u.i = -1;
  }else{
    pOut->u.i = x;
  }
  break;
}

/* Opcode: IfNotZero P1 P2 * * *
** Synopsis: if r[P1]!=0 then r[P1]--, goto P2
**
** Register P1 must contain an integer.  If the content of register P1 is
** initially greater than zero, then decrement the value in register P1.
** If it is non-zero (negative or positive) and then also jump to P2.  
** If register P1 is initially zero, leave it unchanged and fall through.

*/
case OP_IfNotZero: {        /* jump, in1 */
  pIn1 = &aMem[pOp->p1];
  assert( pIn1->flags&MEM_Int );
  VdbeBranchTaken(pIn1->u.i<0, 2);
  if( pIn1->u.i ){
     if( pIn1->u.i>0 ) pIn1->u.i--;
     goto jump_to_p2;
  }
  break;
}

/* Opcode: DecrJumpZero P1 P2 * * *
** Synopsis: if (--r[P1])==0 goto P2