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diff --git a/src/ieee_float.h b/src/ieee_float.h
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+++ b/src/ieee_float.h
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+/*
+  Copyright 2019-2020 David Robillard <http://drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#ifndef SERD_IEEE_FLOAT_H
+#define SERD_IEEE_FLOAT_H
+
+#include <float.h>
+#include <math.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+static const int      dbl_physical_mant_dig = DBL_MANT_DIG - 1;
+static const uint64_t dbl_mant_mask         = 0x000FFFFFFFFFFFFFull;
+static const uint64_t dbl_expt_mask         = 0x7FF0000000000000ul;
+static const uint64_t dbl_hidden_bit        = 0x0010000000000000ul;
+static const int      dbl_expt_bias         = 0x3FF + DBL_MANT_DIG - 1;
+static const int      dbl_subnormal_expt    = -0x3FF - DBL_MANT_DIG + 2;
+
+/// Return the raw representation of a double
+static inline uint64_t
+double_to_rep(const double d)
+{
+	uint64_t rep;
+	memcpy(&rep, &d, sizeof(rep));
+	return rep;
+}
+
+/// Return true if the lower boundary is closer than the upper boundary
+static inline bool
+double_lower_boundary_is_closer(const double d)
+{
+	const uint64_t rep          = double_to_rep(d);
+	const uint64_t mant         = rep & dbl_mant_mask;
+	const uint64_t expt         = rep & dbl_expt_mask;
+	const bool     is_subnormal = expt == 0;
+
+	// True when f = 2^(p-1) (except for the smallest normal)
+	return !is_subnormal && mant == 0;
+}
+
+#endif // SERD_IEEE_FLOAT_H