multibit, fatbit: make _size build-time only

This commit makes mmbit_size() and fatbit_size compile-time only, and
adds a resource limit for very large multibits.

src/util/multibit_build.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, Intel Corporation
+ * Copyright (c) 2015-2016, Intel Corporation
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -34,6 +34,7 @@
 #include "scatter.h"
 #include "ue2common.h"
 #include "rose/rose_build_scatter.h"
+#include "util/compile_error.h"
 
 #include <cassert>
 #include <cstring> // for memset
@@ -45,6 +46,32 @@ using namespace std;
 
 namespace ue2 {
 
+u32 mmbit_size(u32 total_bits) {
+    if (total_bits > MMB_MAX_BITS) {
+        throw ResourceLimitError();
+    }
+
+    // Flat model multibit structures are just stored as a bit vector.
+    if (total_bits <= MMB_FLAT_MAX_BITS) {
+        return ROUNDUP_N(total_bits, 8) / 8;
+    }
+
+    u64a current_level = 1; // Number of blocks on current level.
+    u64a total = 0;         // Total number of blocks.
+    while (current_level * MMB_KEY_BITS < total_bits) {
+        total += current_level;
+        current_level <<= MMB_KEY_SHIFT;
+    }
+
+    // Last level is a one-for-one bit vector. It needs room for total_bits
+    // elements, rounded up to the nearest block.
+    u64a last_level = ((u64a)total_bits + MMB_KEY_BITS - 1) / MMB_KEY_BITS;
+    total += last_level;
+
+    assert(total * sizeof(MMB_TYPE) <= UINT32_MAX);
+    return (u32)(total * sizeof(MMB_TYPE));
+}
+
 namespace {
 struct TreeNode {
     MMB_TYPE mask = 0;
@@ -133,6 +160,7 @@ void mmbBuildSparseIterator(vector<mmbit_sparse_iter> &out,
     assert(out.empty());
     assert(!bits.empty());
     assert(total_bits > 0);
+    assert(total_bits <= MMB_MAX_BITS);
 
     DEBUG_PRINTF("building sparse iter for %zu of %u bits\n",
                  bits.size(), total_bits);