+From: "Douglas C. Schmidt" <schmidt@dre.vanderbilt.edu>
+To: Robert Roebling <robert.roebling@uni-ulm.de>
+Subject: Re: qsort licence
+Date: Mon, 23 Jul 2007 03:44:25 -0500
+Sender: schmidt@dre.vanderbilt.edu
+Message-Id: <20070723084426.64F511000A8@tango.dre.vanderbilt.edu>
+
+Hi Robert,
+
+> [...] I'm asking if you'd be willing to relicence your code
+> under the wxWindows licence. [...]
+
+That's fine with me [...]
+
+Thanks,
+
+ Doug */
+
+
+/* Byte-wise swap two items of size SIZE. */
+#define SWAP(a, b, size) \
+ do \
+ { \
+ register size_t __size = (size); \
+ register 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 4 #defines implement a very fast in-line stack abstraction. */
+#define STACK_SIZE (8 * sizeof(unsigned long int))
+#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
+#define POP(low, high) ((void) (--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 MAX_INT is allocated on the
+ stack. Assuming a 32-bit integer, this needs only 32 *
+ sizeof(stack_node) == 136 bits. 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 (n)
+ stack size is needed (actually O(1) in this case)! */
+
+void wxQsort(void *const pbase, size_t total_elems,
+ size_t size, CMPFUNCDATA cmp, const void* user_data)
+{
+ register char *base_ptr = (char *) pbase;
+ const size_t max_thresh = MAX_THRESH * size;
+
+ if (total_elems == 0)
+ /* Avoid lossage with unsigned arithmetic below. */
+ return;
+
+ if (total_elems > MAX_THRESH)
projects / wxWidgets.git / blobdiff