Added first pass at shrinkler example

tools/external/shrinkler/SizeMeasuringCoder.h

@@ -0,0 +1,60 @@
+// Copyright 1999-2015 Aske Simon Christensen. See LICENSE.txt for usage terms.
+
+/*
+
+A dummy entropy coder which estimates the size of coded symbols based on
+counts from a CountingCoder.
+
+*/
+
+#pragma once
+
+#include <vector>
+
+using std::vector;
+
+#include "CountingCoder.h"
+
+struct ContextSizes {
+	unsigned short sizes[2];
+};
+
+class SizeMeasuringCoder : public Coder {
+	static const int MIN_SIZE = 2;
+	static const int MAX_SIZE = 12 << BIT_PRECISION;
+
+	vector<ContextSizes> context_sizes;
+
+	int sizeForCount(int count, int total) {
+		int size = (int) floor(0.5 + log(total / (double) count) / log(2.0) * (1 << BIT_PRECISION));
+		if (size < MIN_SIZE) size = MIN_SIZE;
+		if (size > MAX_SIZE) size = MAX_SIZE;
+		return size;
+	}
+
+public:
+	SizeMeasuringCoder(int n_contexts) {
+		struct ContextSizes default_sizes = { { 1 << BIT_PRECISION, 1 << BIT_PRECISION } };
+		context_sizes.resize(n_contexts, default_sizes);
+		setCacheable(true);
+	}
+
+	SizeMeasuringCoder(CountingCoder *counting_coder) {
+		context_sizes.resize(counting_coder->context_counts.size());
+		for (int i = 0 ; i < counting_coder->context_counts.size() ; i++) {
+			struct ContextSizes s;
+			struct ContextCounts c = counting_coder->context_counts[i];
+			int count0 = 1 + c.counts[0];
+			int count1 = 1 + c.counts[1];
+			int sum = count0 + count1;
+			s.sizes[0] = sizeForCount(count0, sum);
+			s.sizes[1] = sizeForCount(count1, sum);
+			context_sizes[i] = s;
+		}
+		setCacheable(true);
+	}
+
+	virtual int code(int context_index, int bit) {
+		return context_sizes[context_index].sizes[bit];
+	}
+};