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

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

diff --git a/mingwrt/mingwex/insque.c b/mingwrt/mingwex/insque.c
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+/*
+ * insque.c
+ *
+ * POSIX.1-1996 compatible doubly-linked list management API; provides the
+ * insque() function, for element insertion at 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
+ * arguments specified as pointers to structures of the preceding type,
+ * offers a conventient mechanism for mapping the generic pointers of
+ * the public API to the minimal required form.
+ */
+__CRT_ALIAS void do_insque( struct qnode *element, struct qnode *pred )
+{
+  /* Insert "element" into the list containing "pred", with insertion
+   * point immediately following "pred"; becomes a no-op, if "element"
+   * is specified as NULL...
+   */
+  if( element != NULL )
+  {
+    /* ...otherwise, sets the forward link of "element" to the current
+     * forward link of "pred", (or to NULL, if "pred" is NULL), and the
+     * backward link of the successor to "pred", if any, to point back
+     * to "element"...
+     */
+    if( (element->fwdlink = (pred != NULL) ? pred->fwdlink : NULL) != NULL )
+      element->fwdlink->bkwdlink = element;
+
+    /* ...and completes the linking, by setting the backward link of
+     * "element" to point to "pred", and the forward link of "pred",
+     * (if "pred" isn't NULL), to point to "element".
+     */
+    if( (element->bkwdlink = pred) != NULL )
+      pred->fwdlink = element;
+  }
+}
+
+/* The public API simply expands the inline implementation, mapping
+ * the generic pointer arguments to the minimally specified structure.
+ */
+void insque( void *element, void *pred )
+{ do_insque( (struct qnode *)(element), (struct qnode *)(pred) ); }
+
+/* $RCSfile$: end of file */