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Annotation of 42BSD/ingres/source/ctlmod/init_qt.c, revision 1.1.1.1

1.1       root        1: # include      "ctlmod.h"
                      2: # include      <ingres.h>
                      3: # include      <aux.h>
                      4: # include      <tree.h>
                      5: # include      <sccs.h>
                      6: 
                      7: SCCSID(@(#)init_qt.c   7.1     2/5/81)
                      8: 
                      9: /*
                     10: **  INIT_QT -- initialize query tree
                     11: **
                     12: **     This routine saves and initializes the global portion
                     13: **     of a query tree.  It must be called before doing any
                     14: **     creation of a query tree which depends on or modifies
                     15: **     the global portion of a query tree.
                     16: **
                     17: **     The global portion of a query tree includes the range
                     18: **     table, the query mode, etc.
                     19: **
                     20: **     The algorithm for saving the query tree global portion
                     21: **     ("Qt") is somewhat obscure.  To understand it, it is
                     22: **     critical to be clear that every query tree is associated
                     23: **     with a context, but not every context is associated with
                     24: **     a query tree.  We further constrain that a context
                     25: **     is associated with at most one query tree; if more than
                     26: **     one is needed in a single context, it is always safe
                     27: **     to reuse the previous one.
                     28: **
                     29: **     When we allocate a new context (in 'initp'), the current
                     30: **     Qt (if in use) is associated with the save image of the
                     31: **     context.  When we call init_qt, we check to see if such
                     32: **     an association exists.  If so, we save Qt, and adjust
                     33: **     the old context to point to the save image of Qt.  When
                     34: **     we call init_qt again, Qt will be active, but not
                     35: **     associated with a context save image; thus, we do not
                     36: **     save Qt.  On context restore, if it has a pointer to a
                     37: **     saved Qt, we restore that also.
                     38: **
                     39: **     Parameters:
                     40: **             none.
                     41: **     
                     42: **     Returns:
                     43: **             none
                     44: **     
                     45: **     Side Effects:
                     46: **             Qt possibly gets saved in an area set up by
                     47: **                     calling malloc.
                     48: **     
                     49: **     Trace Flags:
                     50: **             none
                     51: */
                     52: 
                     53: init_qt()
                     54: {
                     55:        extern char     *malloc();
                     56:        register char   *p;
                     57: 
                     58:        /*
                     59:        **  Save Qt if associated with a saved context.
                     60:        */
                     61: 
                     62:        if (Qt.qt_ctx != NULL)
                     63:        {
                     64:                p = malloc(sizeof Qt);
                     65:                if (p == NULL)
                     66:                        syserr("init_qt: no mem");
                     67:                bmove((char *)&Qt, p, sizeof Qt);
                     68:                ((ctx_t *)Qt.qt_ctx)->ctx_qt = p;
                     69:                Qt.qt_ctx = NULL;
                     70:        }
                     71: 
                     72:        /* mark the Qt as active */
                     73:        Qt.qt_active++;
                     74: }

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