Move wikisort/grailsort common code to a shared header

1 files changed, 107 insertions, 0 deletions

diff --git a/common.h b/common.h
new file mode 100644
index 0000000..984d890
--- /dev/null
+++ b/common.h
@@ -0,0 +1,107 @@
+#include <stddef.h>
+#include <stdint.h>
+
+#include "sorters.h"
+
+static void swap(char *a, char *b, size_t width)
+{
+	while (width--) {
+		char tmp = *a;
+		*a++ = *b;
+		*b++ = tmp;
+	}
+}
+
+static void reverse(char *base, size_t nmel, size_t width)
+{
+	char *last = base + (nmel - 1) * width;
+	while (last > base) {
+		swap(base, last, width);
+		base += width;
+		last -= width;
+	}
+}
+
+/* rotates left */
+static void rotate(char *base, size_t nmel, size_t width, size_t shift)
+{
+	reverse(base, shift, width);
+	reverse(base + shift * width, nmel - shift, width);
+	reverse(base, nmel, width);
+}
+
+/* If a matching element exists, returns index of one of them.
+   If none exists, returns index where such an element should be inserted. */
+static size_t binary_search(const char *needle, char *haystack, size_t nmel, size_t width, cmpfun cmp)
+{
+	size_t baseidx = 0;
+	while (nmel) {
+		size_t tryidx = baseidx + nmel / 2;
+		char *try = haystack + tryidx * width;
+		int sign = cmp(try, needle);
+		if (!sign) return tryidx;
+		else if (sign < 0) {
+			baseidx = tryidx + 1;
+			nmel -= nmel / 2 + 1;
+		}
+		else {
+			nmel /= 2;
+		}
+	}
+	return baseidx;
+}
+
+static void distribute_buffer(char *base, size_t bufnmel, size_t sortnmel, size_t width, cmpfun cmp)
+{
+	char *sorted = base + bufnmel * width;
+	while (bufnmel) {
+		char *last = sorted - width;
+		size_t equals;
+		for (equals = 1; equals < bufnmel; equals++) {
+			if (cmp(last, last - equals * width)) break;
+		}
+
+		size_t insertpos = binary_search(last, sorted, sortnmel, width, cmp);
+		rotate(sorted - equals * width, insertpos + equals, width, equals);
+
+		bufnmel  -= equals;
+		sortnmel += equals;
+		sorted   -= equals * width;
+	}
+}
+
+#define MAX_SORTNET 8
+
+static const uint8_t sortnet[][2] = {
+	/* 0: index =  0 */
+	/* 1: index =  0 */
+	/* 2: index =  0 */
+	{0,1},
+	/* 3: index =  1 */
+	{0,1}, {0,2}, {1,2},
+	/* 4: index =  4 */
+	{0,1}, {2,3}, {0,2}, {1,3}, {1,2},
+	/* 5: index =  9 */
+	{0,1}, {3,4}, {2,4}, {2,3}, {1,4}, {0,3}, {0,2}, {1,3}, {1,2},
+	/* 6: index = 18 */
+	{1,2}, {4,5}, {0,2}, {3,5}, {0,1}, {3,4}, {2,5}, {0,3}, {1,4}, {2,4},
+	{1,3}, {2,3},
+	/* 7: index = 30 */
+	{1,2}, {3,4}, {5,6}, {0,2}, {3,5}, {4,6}, {0,1}, {4,5}, {2,6}, {0,4},
+	{1,5}, {0,3}, {2,5}, {1,3}, {2,4}, {2,3},
+	/* 8: index = 46 */
+	{0,1}, {2,3}, {4,5}, {6,7}, {0,2}, {1,3}, {4,6}, {5,7}, {1,2}, {5,6},
+	{0,4}, {3,7}, {1,5}, {2,6}, {1,4}, {3,6}, {2,4}, {3,5}, {3,4},
+	/* 9: index = 65, if we used a sorting network this large */
+};
+
+static const uint8_t sortnet_index[] = { 0, 0, 0, 1, 4, 9, 18, 30, 46, 65 };
+
+static void sorting_network(char *base, size_t nmel, size_t width, cmpfun cmp)
+{
+	for (int i = sortnet_index[nmel]; i < sortnet_index[nmel+1]; i++) {
+		char *elem1 = base + sortnet[i][0] * width;
+		char *elem2 = base + sortnet[i][1] * width;
+		if (cmp(elem1, elem2) > 0) swap(elem1, elem2, width);
+	}
+}