Defer the {quote: MoveTo}

opcode in VDBE until the data is actually needed.  Sometimes
the data is never needed, resulting in a performance increase.  On an indexed
order search with a large OFFSET, queries times can be an order of magnitude
faster. (CVS 1165)

FossilOrigin-Name: d3e96da20d269a068188915b3cc0eb02d330d316

src/vdbeaux.c

@@ -992,3 +992,51 @@ void sqliteVdbeDelete(Vdbe *p){
   p->magic = VDBE_MAGIC_DEAD;
   sqliteFree(p);
 }
+
+/*
+** Convert an integer in between the native integer format and
+** the bigEndian format used as the record number for tables.
+**
+** The bigEndian format (most significant byte first) is used for
+** record numbers so that records will sort into the correct order
+** even though memcmp() is used to compare the keys.  On machines
+** whose native integer format is little endian (ex: i486) the
+** order of bytes is reversed.  On native big-endian machines
+** (ex: Alpha, Sparc, Motorola) the byte order is the same.
+**
+** This function is its own inverse.  In other words
+**
+**         X == byteSwap(byteSwap(X))
+*/
+int sqliteVdbeByteSwap(int x){
+  union {
+     char zBuf[sizeof(int)];
+     int i;
+  } ux;
+  ux.zBuf[3] = x&0xff;
+  ux.zBuf[2] = (x>>8)&0xff;
+  ux.zBuf[1] = (x>>16)&0xff;
+  ux.zBuf[0] = (x>>24)&0xff;
+  return ux.i;
+}
+
+/*
+** If a MoveTo operation is pending on the given cursor, then do that
+** MoveTo now.  Return an error code.  If no MoveTo is pending, this
+** routine does nothing and returns SQLITE_OK.
+*/
+int sqliteVdbeCursorMoveto(Cursor *p){
+  if( p->deferredMoveto ){
+    int res;
+    extern int sqlite_search_count;
+    sqliteBtreeMoveto(p->pCursor, (char*)&p->movetoTarget, sizeof(int), &res);
+    p->lastRecno = keyToInt(p->movetoTarget);
+    p->recnoIsValid = res==0;
+    if( res<0 ){
+      sqliteBtreeNext(p->pCursor, &res);
+    }
+    sqlite_search_count++;
+    p->deferredMoveto = 0;
+  }
+  return SQLITE_OK;
+}