adding btree delete

Author: xtaci

include/btree.h

@@ -29,9 +29,10 @@
 #include <memory>
 
 #define BLOCKSIZE4096
-#define T 255
-#define LEAF 0x0001
-#define ONDISK0x0002
+#define T 255
+#define LEAF 0x0001
+#define ONDISK0x0002
+#define MARKFREE0x0004
 
 namespace alg {
 class BTree {
@@ -217,7 +218,7 @@ namespace alg {
 }
 
 /**
- * recursion deletion
+ * recursive deletion.
  */
 void delete_op(node x, int32_t k) {
 int32_t i;
@@ -240,22 +241,53 @@ namespace alg {
 node y= READ(x, i-1);
 if (y->n >= T) {// case 2a
 x->key[i] = y->key[y->n-1];// subsitute the key with predecessor
+WRITE(x);
+
 delete_op(y, x->key[i]);
 free(y);
 return;
 }
+free(y);
 
 node z = READ(x, i+1);
 if (z->n >= T) {// case 2b
 x->key[i] = z->key[0];
+WRITE(x);
 delete_op(z, x->key[i]);
 return;
 }
+free(z);
 
 // case 2c:
 if (y->n == T-1 && z->n == T-1) {
+// merge k & z into y
+y->key[y->n] = k;
 
+int j;
+for (j=0;j<z->n;j++) {// merge n keys, k already in 
+y->key[y->n+j+1] = z->key[j];
+}
+for (j=0;j<z->n+1;j++) {// merge n+1 childs
+y->c[y->n+j+1] = z->key[j];
+}
+// mark free this node
+z->flag |= MARKFREE;
+y->n = y->n + z->n + 1; // size after merge
+WRITE(z);
+WRITE(y);
+
+// shift x
+for (j=i;j<x->n-1;j++) {
+x->key[i] = x->key[i+1];
+}
+x->n = x->n - 1;
+WRITE(x);
+
+// recursive delete k
+delete_op(y, k);
+return;
 }
+
 delete_case3(x);
 }
 }