[PATCH] 2.6.6 add qsort library function (UPDATED PATCH, symbol exported _GPL)

[Chris Wedgwood]

 [ This is an updated patch where the symbol is exported GPL only
   recognized the GPL origin in the code used.  Thanks for those
   people who pointed this out. ]

This is a rehash of a patch from Andreas Gruenbacher <agruen@xxxxxxx>
to add qsort as a kernel library function.  Right now the only user of
this is XFS others users are expected.

The stack utilization is fairly modest and the function is not
recursive.

I stupidly took the gnu-formatted function and ran Lindent over it
which made a bit of a mess (I manually fixed most of this and am
guilty of editing the diff...)


   --cw


 include/linux/kernel.h |    2
 lib/Kconfig            |    3
 lib/Makefile           |    1
 lib/qsort.c            |  239 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 245 insertions(+)



diff -Nru a/include/linux/kernel.h b/include/linux/kernel.h
--- a/include/linux/kernel.h	Sun May  9 20:27:15 2004
+++ b/include/linux/kernel.h	Sun May  9 20:27:15 2004
@@ -80,6 +80,8 @@
 	__attribute__ ((format (scanf,2,3)));
 extern int vsscanf(const char *, const char *, va_list);
 
+extern void qsort(void *, size_t, size_t, int (*)(const void *,const void *));
+
 extern int get_option(char **str, int *pint);
 extern char *get_options(const char *str, int nints, int *ints);
 extern unsigned long long memparse(char *ptr, char **retptr);
diff -Nru a/lib/Kconfig b/lib/Kconfig
--- a/lib/Kconfig	Sun May  9 20:27:15 2004
+++ b/lib/Kconfig	Sun May  9 20:27:15 2004
@@ -21,6 +21,9 @@
 	  require M here.  See Castagnoli93.
 	  Module will be libcrc32c.
 
+config QSORT
+	bool "Quick Sort"
+
 #
 # compression support is select'ed if needed
 #
diff -Nru a/lib/Makefile b/lib/Makefile
--- a/lib/Makefile	Sun May  9 20:27:15 2004
+++ b/lib/Makefile	Sun May  9 20:27:15 2004
@@ -20,6 +20,7 @@
 
 obj-$(CONFIG_CRC32)	+= crc32.o
 obj-$(CONFIG_LIBCRC32C)	+= libcrc32c.o
+obj-$(CONFIG_QSORT)	+= qsort.o
 
 obj-$(CONFIG_ZLIB_INFLATE) += zlib_inflate/
 obj-$(CONFIG_ZLIB_DEFLATE) += zlib_deflate/
diff -Nru a/lib/qsort.c b/lib/qsort.c
--- /dev/null	Wed Dec 31 16:00:00 1969
+++ b/lib/qsort.c	Sun May  9 20:27:15 2004
@@ -0,0 +1,239 @@
+/*
+ * qsort implementation for the Linux kernel.
+ *
+ * Original implementation taken form glibc and credited to Douglas
+ * C. Schmidt (schmidt@xxxxxxxxxxx).
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2.  See the file COPYING for more details.
+ */
+
+/*
+ * If you consider tuning this algorithm, you should consult first:
+ * Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
+ * Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993.
+ */
+
+# include <linux/module.h>
+# include <linux/slab.h>
+# include <linux/string.h>
+
+MODULE_LICENSE("GPL");
+
+/* Byte-wise swap two items of size SIZE. */
+#define SWAP(a, b, size)		      \
+  do {					      \
+      size_t __size = (size);		      \
+      char *__a = (a), *__b = (b);	      \
+      do {				      \
+	  char __tmp = *__a;		      \
+	  *__a++ = *__b;		      \
+	  *__b++ = __tmp;		      \
+	} while (--__size > 0);		      \
+    } while (0)
+
+/* Discontinue quicksort algorithm when partition gets below this
+   size.  This particular magic number was chosen to work best on a
+   Sun 4/260. */
+#define MAX_THRESH 4
+
+/* Stack node declarations used to store unfulfilled partition
+ * obligations. */
+typedef struct {
+	char *lo;
+	char *hi;
+} stack_node;
+
+/* The next 5 #defines implement a very fast in-line stack
+ * abstraction.  The stack needs log (total_elements) entries (we
+ * could even subtract log(MAX_THRESH)).  Since total_elements has
+ * type size_t, we get as upper bound for log (total_elements): bits
+ * per byte (CHAR_BIT) * sizeof(size_t).  */
+
+#define CHAR_BIT 8
+#define STACK_SIZE	(CHAR_BIT * sizeof(size_t))
+#define PUSH(low, high)	((top->lo = (low)), (top->hi = (high)), ++top)
+#define	POP(low, high)	(--top, (low = top->lo), (high = top->hi))
+#define	STACK_NOT_EMPTY	(stack < top)
+
+/* Order size using quicksort.  This implementation incorporates four
+   optimizations discussed in Sedgewick:
+
+   1. Non-recursive, using an explicit stack of pointer that store the
+   next array partition to sort.  To save time, this maximum amount
+   of space required to store an array of SIZE_MAX is allocated on
+   the stack.  Assuming a 32-bit (64 bit) integer for size_t, this
+   needs only 32 * sizeof(stack_node) == 256 bytes (for 64 bit:
+   1024 bytes).  Pretty cheap, actually.
+
+   2. Chose the pivot element using a median-of-three decision tree.
+   This reduces the probability of selecting a bad pivot value and
+   eliminates certain extraneous comparisons.
+
+   3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
+   insertion sort to order the MAX_THRESH items within each
+   partition.  This is a big win, since insertion sort is faster
+   for small, mostly sorted array segments.
+
+   4. The larger of the two sub-partitions is always pushed onto the
+   stack first, with the algorithm then concentrating on the
+   smaller partition.  This *guarantees* no more than log
+   (total_elems) stack size is needed (actually O(1) in this case)!
+*/
+
+void
+qsort(void *const pbase, size_t total_elems, size_t size,
+      int (*cmp)(const void*, const void*))
+{
+	char *base_ptr = (char *)pbase;
+
+	const size_t max_thresh = MAX_THRESH * size;
+
+	/* Avoid lossage with unsigned arithmetic below.  */
+	if (total_elems == 0) {
+		return;
+	}
+
+	if (total_elems > MAX_THRESH) {
+		char *lo = base_ptr;
+		char *hi = &lo[size * (total_elems - 1)];
+		stack_node stack[STACK_SIZE];
+		stack_node *top = stack + 1;
+
+		while (STACK_NOT_EMPTY) {
+			char *left_ptr;
+			char *right_ptr;
+
+			/* Select median value from among LO, MID, and
+			   HI. Rearrange LO and HI so the three values
+			   are sorted. This lowers the probability of
+			   picking a pathological pivot value and
+			   skips a comparison for both the LEFT_PTR
+			   and RIGHT_PTR in the while loops. */
+
+			char *mid = lo + size * ((hi - lo) / size >> 1);
+
+			if ((*cmp)((void*)mid, (void*)lo) < 0)
+				SWAP(mid, lo, size);
+			if ((*cmp)((void*)hi, (void*)mid) < 0)
+				SWAP(mid, hi, size);
+			else
+				goto jump_over;
+			if ((*cmp)((void*)mid, (void*)lo) < 0)
+				SWAP(mid, lo, size);
+		jump_over:
+
+			left_ptr = lo + size;
+			right_ptr = hi - size;
+
+			/* Here's the famous ``collapse the walls''
+			   section of quicksort.  Gotta like those
+			   tight inner loops!  They are the main
+			   reason that this algorithm runs much faster
+			   than others. */
+			do {
+				while ((*cmp)((void*)left_ptr, (void*)mid) < 0)
+					left_ptr += size;
+
+				while ((*cmp)((void*)mid, (void*)right_ptr) < 0)
+					right_ptr -= size;
+
+				if (left_ptr < right_ptr) {
+					SWAP(left_ptr, right_ptr, size);
+					if (mid == left_ptr)
+						mid = right_ptr;
+					else if (mid == right_ptr)
+						mid = left_ptr;
+					left_ptr += size;
+					right_ptr -= size;
+				} else if (left_ptr == right_ptr) {
+					left_ptr += size;
+					right_ptr -= size;
+					break;
+				}
+			}
+			while (left_ptr <= right_ptr);
+
+			/* Set up pointers for next iteration.  First
+			   determine whether left and right partitions
+			   are below the threshold size.  If so,
+			   ignore one or both.  Otherwise, push the
+			   larger partition's bounds on the stack and
+			   continue sorting the smaller one. */
+
+			if ((size_t) (right_ptr - lo) <= max_thresh) {
+				if ((size_t) (hi - left_ptr) <= max_thresh)
+					/* Ignore both small partitions. */
+					POP(lo, hi);
+				else
+					/* Ignore small left partition. */
+					lo = left_ptr;
+			} else if ((size_t) (hi - left_ptr) <= max_thresh)
+				/* Ignore small right partition. */
+				hi = right_ptr;
+			else if ((right_ptr - lo) > (hi - left_ptr)) {
+				/* Push larger left partition indices. */
+				PUSH(lo, right_ptr);
+				lo = left_ptr;
+			} else {
+				/* Push larger right partition indices. */
+				PUSH(left_ptr, hi);
+				hi = right_ptr;
+			}
+		}
+	}
+
+	/* Once the BASE_PTR array is partially sorted by quicksort
+	   the rest is completely sorted using insertion sort, since
+	   this is efficient for partitions below MAX_THRESH
+	   size. BASE_PTR points to the beginning of the array to
+	   sort, and END_PTR points at the very last element in the
+	   array (*not* one beyond it!). */
+
+	{
+		char *end_ptr = &base_ptr[size * (total_elems - 1)];
+		char *tmp_ptr = base_ptr;
+		char *thresh = min(end_ptr, base_ptr + max_thresh);
+		char *run_ptr;
+
+		/* Find smallest element in first threshold and place
+		   it at the array's beginning.  This is the smallest
+		   array element, and the operation speeds up
+		   insertion sort's inner loop. */
+
+		for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
+			if ((*cmp)((void*)run_ptr, (void*)tmp_ptr) < 0)
+				tmp_ptr = run_ptr;
+
+		if (tmp_ptr != base_ptr)
+			SWAP(tmp_ptr, base_ptr, size);
+
+		/* Insertion sort, running from left-hand-side up to
+		 * right-hand-side.  */
+
+		run_ptr = base_ptr + size;
+		while ((run_ptr += size) <= end_ptr) {
+			tmp_ptr = run_ptr - size;
+			while ((*cmp)((void*)run_ptr, (void*)tmp_ptr) < 0)
+				tmp_ptr -= size;
+
+			tmp_ptr += size;
+			if (tmp_ptr != run_ptr) {
+				char *trav;
+
+				trav = run_ptr + size;
+				while (--trav >= run_ptr) {
+					char c = *trav;
+					char *hi, *lo;
+
+					for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
+						*hi = *lo;
+					*hi = c;
+				}
+			}
+		}
+	}
+}
+
+EXPORT_SYMBOL_GPL(qsort);
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