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Subject[PATCH] 2.6.6 add qsort library function
This is a rehash of a patch from Andreas Gruenbacher <agruen@suse.de>
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@ics.uci.edu).
+ *
+ * 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(qsort);
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