Fix a bug where allocator was unable to allocate up to last (n%64) blocks, add tests for it

src/test_allocator.cpp

@@ -2,20 +2,39 @@
 // License: VNPL-1.1 (see README.md for details)
 
 #include <stdio.h>
+#include <stdlib.h>
 #include "allocator.h"
 
+void alloc_all(int size)
+{
+    allocator *a = new allocator(size);
+    for (int i = 0; i < size; i++)
+    {
+        uint64_t x = a->find_free();
+        if (x == UINT64_MAX)
+        {
+            printf("ran out of space %d allocated=%d\n", size, i);
+            exit(1);
+        }
+        if (x != i)
+        {
+            printf("incorrect block allocated: expected %d, got %lu\n", i, x);
+        }
+        a->set(x, true);
+    }
+    uint64_t x = a->find_free();
+    if (x != UINT64_MAX)
+    {
+        printf("extra free space found: %lx (%d)\n", x, size);
+        exit(1);
+    }
+    delete a;
+}
+
 int main(int narg, char *args[])
 {
-    allocator a(8192);
-    for (int i = 0; i < 8192; i++)
-    {
-        uint64_t x = a.find_free();
-        if (x == UINT64_MAX)
-        {
-            printf("ran out of space %d\n", i);
-            return 1;
-        }
-        a.set(x, true);
-    }
+    alloc_all(8192);
+    alloc_all(8062);
+    alloc_all(4096);
     return 0;
 }