Implement POSIX.1-1996 linked-list queue management API.

[mingw/mingw-org-wsl.git] / mingwrt / mingwex / remque.c

diff --git a/mingwrt/mingwex/remque.c b/mingwrt/mingwex/remque.c
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+/*
+ * remque.c
+ *
+ * POSIX.1-1996 compatible doubly-linked list management API; provides the
+ * remque() function, for removal of an element from an arbitrary position
+ * within a linear, or circular, doubly-linked list.
+ *
+ *
+ * $Id$
+ *
+ * Written by Keith Marshall <keith@users.osdn.me>
+ * Copyright (C) 2018, MinGW.org Project.
+ *
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice, this permission notice, and the following
+ * disclaimer shall be included in all copies or substantial portions of
+ * the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OF OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ */
+#include <search.h>
+#include <stddef.h>
+
+/* This private structure definition specifies the minimal layout of a
+ * doubly-linked list element; client code will typically append extra
+ * data fields, but the first two fields must be pointers to identical
+ * structures.
+ */
+struct qnode { struct qnode *fwdlink, *bkwdlink; };
+
+/* Providing the actual implementation as an inline function, with its
+ * argument specified as a pointer to a structure of the preceding type,
+ * offers a conventient mechanism for mapping the generic pointer of the
+ * public API to the minimal required form.
+ */
+__CRT_ALIAS void do_remque( struct qnode *element )
+{
+  /* Remove "element" from the list which contains it; becomes a
+   * no-op, if "element" is NULL...
+   */
+  if( element != NULL )
+  {
+    /* ...otherwise, updates the backward link in the successor of
+     * "element", if any, to point to the predecessor of "element"...
+     */
+    if( element->fwdlink != NULL )
+      element->fwdlink->bkwdlink = element->bkwdlink;
+
+    /* ...and the forward link in the predecessor of "element", if
+     * any, to point to the successor of "element".
+     */
+    if( element->bkwdlink != NULL )
+      element->bkwdlink->fwdlink = element->fwdlink;
+  }
+}
+
+/* The public API simply expands the inline implementation, mapping
+ * the generic pointer argument to the minimally specified structure.
+ */
+void remque( void *element )
+{ do_remque( (struct qnode *)(element) ); }
+
+/* $RCSfile$: end of file */