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diff --git a/ryg_rans/renormalize.h b/ryg_rans/renormalize.h
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+#ifndef RENORMALIZE_H_INCLUDED
+#define RENORMALIZE_H_INCLUDED
+
+// Optimal renormalization of a frequency table down to a more coarse-grained
+// table; through a combination of heuristics and memoization, finds the
+// rounding that produces the fewest amount of bits needed to encode, while
+// making sure no symbol gets a frequency of zero. Primarily useful for when
+// your precision is low enough that loss is a real problem; compared to direct
+// rounding, it tends to cut the overhead about in half.
+//
+// This operation is cheap but not free; it seems to use 1–2 ms on a Haswell 2.1 GHz
+// for 256 symbols (the speed is mostly dependent on number of symbols, although
+// number of bits also matters some).
+
+#include <stdint.h>
+
+void OptimalRenormalize(uint32_t *cum_freqs, uint32_t num_syms, uint32_t target_total);
+
+#endif // RENORMALIZE_H_INCLUDED