crlib: reduce hashmap memory usage.

build: fixed clang build.

ext/crlib/cr-hashmap.h

@@ -103,8 +103,15 @@ private:
       return hash_ (key) % length;
    }
 
-   void rehash () {
-      auto capacity = (capacity_ << 1);
+   void rehash (size_t targetCapacity) {
+      if (length_ + targetCapacity < capacity_) {
+         return;
+      }
+      auto capacity = capacity_ ? capacity_ : 3;
+
+      while (length_ + targetCapacity > capacity) {
+         capacity *= 2;
+      }
       auto contents = cr::makeUnique <Entries> (capacity);
 
       for (size_t i = 0; i < capacity_; ++i) {
@@ -188,7 +195,7 @@ public:
       for (size_t i = 0; i < capacity_; ++i) {
          contents_[i].used = false;
       }
-      rehash ();
+      rehash (0);
    }
 
    void foreach (Lambda <void (const K &, const V &)> callback) {
@@ -201,8 +208,8 @@ public:
 
 public:
    V &operator [] (const K &key) {
-      if ((length_ << 1) > capacity_) {
-         rehash ();
+      if (length_ >= capacity_) {
+         rehash (length_ << 1);
       }
       auto result = put (key, contents_, capacity_);