Initial Spring 2016 commit.

userland/lib/libc/stdlib/qsort.c

@@ -0,0 +1,145 @@
+/*
+ * Copyright (c) 2014
+ *	The President and Fellows of Harvard College.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+/*
+ * qsort() for OS/161, where it isn't in libc.
+ */
+void
+qsort(void *vdata, unsigned num, size_t size,
+      int (*f)(const void *, const void *))
+{
+	unsigned pivot, head, tail;
+	char *data = vdata;
+	char tmp[size];
+
+#define COMPARE(aa, bb) \
+		((aa) == (bb) ? 0 : f(data + (aa) * size, data + (bb) * size))
+#define EXCHANGE(aa, bb) \
+		memcpy(tmp, data + (aa) * size, size);			\
+		memcpy(data + (aa) * size, data + (bb) * size, size);	\
+		memcpy(data + (bb) * size, tmp, size)
+
+
+	if (num <= 1) {
+		return;
+	}
+	if (num == 2) {
+		if (COMPARE(0, 1) > 0) {
+			EXCHANGE(0, 1);
+			return;
+		}
+	}
+
+	/*
+	 * 1. Pick a pivot value. For simplicity, always use the
+	 * middle of the array.
+	 */
+	pivot = num / 2;
+
+	/*
+	 * 2. Shift all values less than or equal to the pivot value
+	 * to the front of the array.
+	 */
+	head = 0;
+	tail = num - 1;
+
+	while (head < tail) {
+		if (COMPARE(head, pivot) <= 0) {
+			head++;
+		}
+		else if (COMPARE(tail, pivot) > 0) {
+			tail--;
+		}
+		else {
+			EXCHANGE(head, tail);
+			if (pivot == head) {
+				pivot = tail;
+			}
+			else if (pivot == tail) {
+				pivot = head;
+			}
+			head++;
+			tail--;
+		}
+	}
+
+	/*
+	 * 3. If there's an even number of elements and we swapped the
+	 * last two, the head and tail indexes will cross. In this
+	 * case the first entry on the tail side is tail+1. If there's
+	 * an odd number of elements, we stop with head == tail, and
+	 * the first entry on the tail side is this value (hence,
+	 * tail) if it's is greater than the pivot value, and the next
+	 * element (hence, tail+1) if it's less than or equal to the
+	 * pivot value.
+	 *
+	 * Henceforth use "tail" to hold the index of the first entry
+	 * of the back portion of the array.
+	 */
+	if (head > tail || COMPARE(head, pivot) <= 0) {
+		tail++;
+	}
+
+	/*
+	 * 4. If we got a bad pivot that gave us only one partition,
+	 * because of the order of the advances in the loop above it
+	 * will always put everything in the front portion of the
+	 * array (so tail == num). This happens if we picked the
+	 * largest value. Move the pivot to the end, if necessary, lop
+	 * off all values equal to it, and recurse on the rest.  (If
+	 * there is no rest, the array is already sorted and we're
+	 * done.)
+	 */
+	if (tail == num) {
+		if (pivot < num - 1) {
+			if (COMPARE(pivot, num - 1) > 0) {
+				EXCHANGE(pivot, num - 1);
+			}
+		}
+		tail = num - 1;
+		while (tail > 0 && COMPARE(tail - 1, tail) == 0) {
+			tail--;
+		}
+		if (tail > 0) {
+			qsort(vdata, tail, size, f);
+		}
+		return;
+	}
+	assert(tail > 0 && tail < num);
+
+	/*
+	 * 5. Recurse on each subpart of the array.
+	 */
+	qsort(vdata, tail, size, f);
+	qsort((char *)vdata + tail * size, num - tail, size, f);
+}