Initial import of the CDE 2.1.30 sources from the Open Group.

cde/lib/tt/mini_isam/isbtree3.c

@@ -0,0 +1,326 @@
+/*%%  (c) Copyright 1993, 1994 Hewlett-Packard Company			 */
+/*%%  (c) Copyright 1993, 1994 International Business Machines Corp.	 */
+/*%%  (c) Copyright 1993, 1994 Sun Microsystems, Inc.			 */
+/*%%  (c) Copyright 1993, 1994 Novell, Inc. 				 */
+/*%%  $XConsortium: isbtree3.c /main/3 1995/10/23 11:36:12 rswiston $ 			 				 */
+#ifndef lint
+    static char sccsid[] = "@(#)isbtree3.c 1.5 89/07/17 Copyr 1988 Sun Micro";
+#endif
+
+/*
+ * Copyright (c) 1988 by Sun Microsystems, Inc.
+ */
+
+/*
+ * isbtree3.c
+ *
+ * Description:
+ *	B-tree operations: REMOVE
+ *	
+ */
+
+#include "isam_impl.h"
+
+extern int _iskeycmp();
+static remove_entry();
+
+/* _isbtree_remove() - Remove entry from B-tree ----------------------------*/
+
+void
+_isbtree_remove(btree)
+    register Btree	 *btree;
+{
+    struct keydesc2	*pkeydesc2 = btree->keydesc2;
+    int			nkeys;		     /* Number of keys in the page */
+    register int	i;
+    char		*pkp, *pkp2, *pkp3;
+    struct bufhdr	*kp2bhdr;
+    Blkno		blkno2;
+    int			level;
+    int			capac, halfcapac;
+    int			move_keys;
+    
+    /* Set comparison function. */
+    _iskeycmp_set(pkeydesc2, pkeydesc2->k2_nparts+1); /* +1 for recno field */
+    
+    /*
+     * Main loop.
+     *  Remove he current entry from leaf.
+     *  If it was leftmost entry, propagate new leftmost to upper levels.
+     *  If block has less than capac/2 + 1 entries, either move some entries
+     *  from next left or right block, or merge with next left or right
+     *  block.
+     */
+    
+    for (i = btree->depth - 1; i >= 0; i--) {
+	
+	/* Re-fix the current page for update. */
+	btree->bufhdr[i] = _isdisk_refix(btree->bufhdr[i], ISFIXWRITE);
+	pkp = btree->bufhdr[i]->isb_buffer;
+	
+	level = ldshort(pkp + BT_LEVEL_OFF);
+	capac = ldshort(pkp + BT_CAPAC_OFF); /* Block capacity */
+	nkeys = ldshort(pkp + BT_NKEYS_OFF); /* Number of keys in block */
+	
+	halfcapac = (capac+1) >> 1;	     /* same as capac/2 + 1 */
+	
+	assert(level + i + 1 == btree->depth);
+	assert(i == 0 || nkeys >= halfcapac);
+	
+	/* Remove entry from this page. */
+	remove_entry(btree, pkp, btree->curpos[i]);
+	nkeys--;
+	
+	/* Must propagate new leftmost key up. */
+	if (btree->curpos[i] == 0 && i > 0)
+	    leftkey_up(btree, i);
+	
+	if (nkeys >= halfcapac || i == 0) {
+	    
+	    /*
+	     * Page is still balanced. No changes are necessary.
+	     * Also, no chages are needed if this is root block.
+	     */
+	    
+	    break;
+	}
+	else {
+	    
+	    if(btree->curpos[i-1] > 0) {
+		
+		/*
+		 * Block pkp is not the leftmost descendent of its parent.
+		 * Either merge with left brother, or move a few entries
+		 * from it.
+		 */
+		
+		pkp3 = btree->bufhdr[i-1]->isb_buffer;
+		
+		blkno2 = ldblkno(pkp3 + ISPAGESIZE - 
+			(btree->curpos[i-1]) * BLKNOSIZE);
+		
+		/* Fix the left brother. */
+		kp2bhdr = _isdisk_fix(btree->fcb, btree->fcb->indfd,
+				      blkno2, ISFIXWRITE);
+		pkp2 = kp2bhdr->isb_buffer;
+		
+		if (ldshort(pkp2 + BT_NKEYS_OFF) + nkeys > capac) {
+		    
+		    /*
+		     * Current page cannot be merged with the left brother.
+		     * Move some entries from the left brother into current.
+		     */
+		    
+		    move_keys = (ldshort(pkp2 + BT_NKEYS_OFF) - halfcapac +1)/2;
+		    assert(move_keys > 0);
+		    
+		    move_from_left (btree, pkp2, pkp, move_keys);
+		    
+		    leftkey_up(btree, i);     /* Propagate new leftmost key */
+		    
+		    break;		     /* From main loop */
+		}
+		else {
+		    
+		    /*
+		     * Current page and left brotehr will be merged.
+		     * Move all entries from current into left, and free
+		     * current.
+		     */
+		    
+		    /* Move all entries from current into left. */
+		    move_from_right(btree, pkp2, pkp, nkeys); 
+		    
+		    /* Free current page. */
+		    _isindfreel_free(btree->fcb, btree->bufhdr[i]->isb_blkno);
+		    
+		    btree->bufhdr[i] = kp2bhdr; /* Update search path */
+		    
+		    /* The loop must iterate to delete entry in parent block. */
+		}
+	    }
+	    else {
+		
+		/*
+		 * Block pkp is the leftmost descendent of its parent.
+		 * Either merge with right brother, or move a few entries
+		 * from it.
+		 */
+		
+		pkp3 = btree->bufhdr[i-1]->isb_buffer;
+		
+		blkno2 = ldblkno(pkp3 + ISPAGESIZE - 
+			(btree->curpos[i-1] + 2) * BLKNOSIZE);
+		
+		/* Fix the right brother. */
+		kp2bhdr = _isdisk_fix(btree->fcb, btree->fcb->indfd,
+				      blkno2, ISFIXWRITE);
+		pkp2 = kp2bhdr->isb_buffer;
+		
+		if (ldshort(pkp2 + BT_NKEYS_OFF) + nkeys > capac) {
+		    
+		    /*
+		     * Current page cannot be merged with the right brother.
+		     * Move some entries from the right brother into current.
+		     */
+		    
+		    move_keys = (ldshort(pkp2 + BT_NKEYS_OFF) - halfcapac +1)/2;
+		    assert(move_keys > 0);
+		    
+		    move_from_right(btree, pkp, pkp2, move_keys);
+		    
+		    /* Update search path to go through right brother. */
+		    btree->curpos[i-1]++;
+		    btree->bufhdr[i] = kp2bhdr;
+		    btree->curpos[i] = 0;
+		    leftkey_up(btree, i);     /* Propagate new leftmost key */
+		    
+		    break;		     /* From main loop */
+		}
+		else {
+		    
+		    /*
+		     * Current page and right brother will be merged.
+		     * Move all entries from right into current, and free
+		     * right.
+		     */
+		    
+		    /* Move all entries from right brother into current. */
+		    move_from_right(btree, pkp, pkp2, ldshort(pkp2 + BT_NKEYS_OFF)); 
+		    
+		    /* Free right brother page. */
+		    _isindfreel_free(btree->fcb, kp2bhdr->isb_blkno);
+		    
+		    /* Update search path to point at right brother*/
+		    btree->curpos[i-1]++;
+		    /* The loop must iterate to delete entry in parent block. */
+
+		}
+	    }
+	}
+    }  /* end of main loop */
+    
+    if (btree->depth > 1) {
+	pkp = btree->bufhdr[0]->isb_buffer;
+	
+	if (ldshort(pkp + BT_NKEYS_OFF) < 2) {
+	    
+	    /*
+	     * Root now has only 1 entry and it is not the sole block.
+	     * Replace root with its only descendant, don't change
+	     * root blkno.
+	     */
+	    pkp2 = btree->bufhdr[1]->isb_buffer;
+	    memcpy( pkp,pkp2, ISPAGESIZE);
+	    
+	    /* Free page. */
+	    _isindfreel_free(btree->fcb, btree->bufhdr[1]->isb_blkno);
+	}
+    }
+}
+
+
+/*--------- remove supporting local functions -------------------------------*/
+
+static remove_entry(btree, pkp, pos)
+    register Btree	*btree;
+    char		*pkp;
+    int			pos;
+{
+    int    		keylength = btree->keydesc2->k2_len;
+    int			nkeys = ldshort(pkp + BT_NKEYS_OFF);
+    int			level = ldshort(pkp + BT_LEVEL_OFF);
+    
+    assert(nkeys > 0);
+    assert(pos >= 0 && pos < nkeys);
+    
+    /* Shift nkeys - pos - 1 entries to the left. */
+    memcpy(pkp + BT_KEYS_OFF + pos * keylength,
+	   pkp + BT_KEYS_OFF + (pos + 1) * keylength,
+	   (nkeys - pos - 1) * keylength);
+    
+    /* For non-leaf nodes, remove block number from table of down pointers. */
+    if (level > 0) {
+	
+	memmove(pkp + ISPAGESIZE - (nkeys - 1) * BLKNOSIZE,
+	       pkp + ISPAGESIZE - nkeys * BLKNOSIZE,
+	       (nkeys - pos - 1) * BLKNOSIZE);
+    }
+    
+    stshort((short) (nkeys - 1), pkp + BT_NKEYS_OFF);
+}
+
+move_from_right(btree, l, r, move_keys)
+    Btree	 *btree;
+    char	*l, *r;
+    int		move_keys;
+{
+    int    	keylength = btree->keydesc2->k2_len;
+    int		lnkeys = ldshort(l + BT_NKEYS_OFF);
+    int		rnkeys = ldshort(r + BT_NKEYS_OFF);
+    int		level = ldshort(r + BT_LEVEL_OFF);
+    
+    /* Move move_keys from l into r block. */
+    memcpy( l + BT_KEYS_OFF + lnkeys * keylength,r + BT_KEYS_OFF,
+	  move_keys * keylength);
+    
+    /* Move remaining entries in r to the left side. */
+    memcpy( r + BT_KEYS_OFF,r + BT_KEYS_OFF + move_keys * keylength,
+	  (rnkeys - move_keys) * keylength);
+    
+    /* If non-leaf, move the pointers stored at the end of block. */
+    if (level > 0) {
+	memcpy(l + ISPAGESIZE - (lnkeys + move_keys) * BLKNOSIZE,
+	       r + ISPAGESIZE - move_keys * BLKNOSIZE,
+	       move_keys * BLKNOSIZE);
+
+	memmove(r + ISPAGESIZE - (rnkeys - move_keys) * BLKNOSIZE,
+	       r + ISPAGESIZE - rnkeys * BLKNOSIZE,
+	       (rnkeys - move_keys) * BLKNOSIZE);
+    }
+    
+    lnkeys += move_keys;
+    rnkeys -= move_keys;
+    
+    stshort((short) lnkeys, l + BT_NKEYS_OFF);
+    stshort((short) rnkeys, r + BT_NKEYS_OFF);
+}
+
+move_from_left(btree, l, r, move_keys)
+    Btree	*btree;
+    char	*l, *r;
+    int		move_keys;
+{
+    int    	keylength = btree->keydesc2->k2_len;
+    int		lnkeys = ldshort(l + BT_NKEYS_OFF);
+    int		rnkeys = ldshort(r + BT_NKEYS_OFF);
+    int		level = ldshort(r + BT_LEVEL_OFF);
+    
+    /* Move entries in r to the right side to create space for move_keys. */
+    memmove( r + BT_KEYS_OFF + move_keys * keylength,r + BT_KEYS_OFF,
+	  rnkeys * keylength);
+    
+    /* Move move_keys from l into r block. */
+    memcpy( r + BT_KEYS_OFF,l + BT_KEYS_OFF + (lnkeys - move_keys) * keylength,
+	  move_keys * keylength);
+    
+    /* If non-leaf,  move the pointers stored at the end of block. */
+    if (level > 0) {
+	
+	memcpy(r + ISPAGESIZE - (rnkeys + move_keys) * BLKNOSIZE,
+	       r + ISPAGESIZE - rnkeys * BLKNOSIZE,
+	       rnkeys * BLKNOSIZE);
+	
+	memcpy(r + ISPAGESIZE - move_keys * BLKNOSIZE,
+	       l + ISPAGESIZE - lnkeys * BLKNOSIZE,
+	       move_keys * BLKNOSIZE);
+    }
+    
+    lnkeys -= move_keys;
+    rnkeys += move_keys;
+    
+    stshort((short) lnkeys, l + BT_NKEYS_OFF);
+    stshort((short) rnkeys, r + BT_NKEYS_OFF);
+}
+
+