mergesort

alglib/src/sort.c

@@ -41,10 +41,12 @@ void upo_insertion_sort(void *base, size_t n, size_t size, upo_sort_comparator_t
 
 void upo_merge_sort(void *base, size_t n, size_t size, upo_sort_comparator_t cmp)
 {
-    /* TO STUDENTS:
-     *  Remove the following two lines and put here your implementation. */
-    fprintf(stderr, "To be implemented!\n");
-    abort();
+    if (n > 1) {
+        void *base2 = (unsigned char *)base + (n / 2) * size;
+        upo_merge_sort(base, n / 2, size, cmp);
+        upo_merge_sort(base2, n - (n / 2), size, cmp);
+        upo_merge_sort_merge(base, n / 2, base2, n - (n / 2), size, cmp);
+    }
 }
 
 void upo_quick_sort(void *base, size_t n, size_t size, upo_sort_comparator_t cmp)

alglib/src/sort_private.c

 #include <assert.h>
 #include "sort_private.h"
+#include <stdlib.h>
+#include <string.h>
 
 void *upo_insertion_sort_insert_pos(
     const void *base,
@@ -17,3 +19,42 @@ void *upo_insertion_sort_insert_pos(
     // unreachable
     assert(0);
 }
+
+void upo_merge_sort_merge(void *base1, size_t n1, void *base2, size_t n2, size_t size, upo_sort_comparator_t cmp)
+{
+    unsigned char *tmp = malloc((n1 + n2) * size);
+
+    size_t i1 = 0;
+    size_t i2 = 0;
+
+    while (i1 < n1 && i2 < n2) {
+        unsigned char *curr1 = (unsigned char *)base1 + i1 * size;
+        unsigned char *curr2 = (unsigned char *)base2 + i2 * size;
+        unsigned char *currtmp = tmp + (i1 + i2) * size;
+        if (cmp(curr1, curr2) < 0) {
+            memcpy(currtmp, curr1, size);
+            ++i1;
+        } else {
+            memcpy(currtmp, curr2, size);
+            ++i2;
+        }
+    }
+
+    while (i1 < n1) {
+        unsigned char *curr = (unsigned char *)base1 + i1 * size;
+        unsigned char *currtmp = tmp + (i1 + i2) * size;
+        memcpy(currtmp, curr, size);
+        ++i1;
+    }
+
+    while (i2 < n2) {
+        unsigned char *curr = (unsigned char *)base2 + i2 * size;
+        unsigned char *currtmp = tmp + (i1 + i2) * size;
+        memcpy(currtmp, curr, size);
+        ++i2;
+    }
+
+    memcpy(base1, tmp, n1 * size);
+    memcpy(base2, tmp + n1 * size, n2 * size);
+    free(tmp);
+}

alglib/src/sort_private.h

@@ -39,6 +39,9 @@ void *upo_insertion_sort_insert_pos(
     upo_sort_comparator_t cmp
 );
 
+void upo_merge_sort_merge(void *base1, size_t n1, void *base2, size_t n2, size_t size, upo_sort_comparator_t cmp);
+
+
 /* TO STUDENTS:
  *
  *  This file is currently "empty".