added a simple implementation for priority queues.

src/runtime/c/Makefile.am

@@ -14,6 +14,7 @@ libpgf_la_SOURCES = \
 	pgf/text.h \
 	pgf/vector.cxx \
 	pgf/vector.h \
+	pgf/heap.h \
 	pgf/pgf.cxx \
 	pgf/reader.cxx \
 	pgf/reader.h \

src/runtime/c/pgf/heap.h

@@ -0,0 +1,78 @@
+#ifndef HEAP_H
+#define HEAP_H
+
+template <class A>
+class PGF_INTERNAL_DECL Heap {
+public:
+    Heap() {
+        len   = 0;
+        avail = 0;
+    }
+
+    ~Heap() { free(values); }
+
+    void push(A value) {
+        if (len >= avail) {
+            avail = get_next_padovan(len);
+            A *new_values = (A *) realloc(values, sizeof(A)*avail);
+            if (new_values == NULL)
+                throw pgf_systemerror(errno);
+            values = new_values;
+        }
+        siftdown(value, 0, len);
+        len++;
+    }
+
+    bool is_empty() { return (len == 0); }
+    
+    A top() { return values[0]; }
+
+    A pop() {
+        A top = values[0];
+        siftup(&values[len-1],0);
+        len--;
+        return top;
+    }
+
+private:
+    size_t len;
+    size_t avail;
+    A *values;
+
+    void siftdown(A value, size_t startpos, size_t pos) {
+        while (pos > startpos) {
+            size_t parentpos = (pos - 1) >> 1;
+            A parent = values[parentpos];
+
+            if (value >= parent)
+                break;
+
+            values[pos] = parent;
+            pos = parentpos;
+        }
+
+        values[pos] = value;
+    }
+    
+    void siftup(A *pvalue, size_t pos) {
+        size_t startpos = pos;
+        size_t endpos   = len;
+
+        size_t childpos = 2*pos + 1;
+        while (childpos < endpos) {
+            size_t rightpos = childpos + 1;
+            if (rightpos < endpos &&
+                values[childpos] >= values[rightpos]) {
+                childpos = rightpos;
+            }
+
+            values[pos] = values[childpos];
+            pos = childpos;
+            childpos = 2*pos + 1;
+       }
+       
+       siftdown(*pvalue, startpos, pos);
+    }
+};
+
+#endif