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diff --git a/src/common/ryu_common.h b/src/common/ryu_common.h
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+/*---------------------------------------------------------------------------
+ *
+ * Common routines for Ryu floating-point output.
+ *
+ * Portions Copyright (c) 2018-2020, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/common/ryu_common.h
+ *
+ * This is a modification of code taken from github.com/ulfjack/ryu under the
+ * terms of the Boost license (not the Apache license). The original copyright
+ * notice follows:
+ *
+ * Copyright 2018 Ulf Adams
+ *
+ * The contents of this file may be used under the terms of the Apache
+ * License, Version 2.0.
+ *
+ *     (See accompanying file LICENSE-Apache or copy at
+ *      http://www.apache.org/licenses/LICENSE-2.0)
+ *
+ * Alternatively, the contents of this file may be used under the terms of the
+ * Boost Software License, Version 1.0.
+ *
+ *     (See accompanying file LICENSE-Boost or copy at
+ *      https://www.boost.org/LICENSE_1_0.txt)
+ *
+ * Unless required by applicable law or agreed to in writing, this software is
+ * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.
+ *
+ *---------------------------------------------------------------------------
+ */
+#ifndef RYU_COMMON_H
+#define RYU_COMMON_H
+
+/*
+ * Upstream Ryu's output is always the shortest possible. But we adjust that
+ * slightly to improve portability: we avoid outputting the exact midpoint
+ * value between two representable floats, since that relies on the reader
+ * getting the round-to-even rule correct, which seems to be the common
+ * failure mode.
+ *
+ * Defining this to 1 would restore the upstream behavior.
+ */
+#define STRICTLY_SHORTEST 0
+
+#if SIZEOF_SIZE_T < 8
+#define RYU_32_BIT_PLATFORM
+#endif
+
+/*  Returns e == 0 ? 1 : ceil(log_2(5^e)). */
+static inline uint32
+pow5bits(const int32 e)
+{
+	/*
+	 * This approximation works up to the point that the multiplication
+	 * overflows at e = 3529.
+	 *
+	 * If the multiplication were done in 64 bits, it would fail at 5^4004
+	 * which is just greater than 2^9297.
+	 */
+	Assert(e >= 0);
+	Assert(e <= 3528);
+	return ((((uint32) e) * 1217359) >> 19) + 1;
+}
+
+/*  Returns floor(log_10(2^e)). */
+static inline int32
+log10Pow2(const int32 e)
+{
+	/*
+	 * The first value this approximation fails for is 2^1651 which is just
+	 * greater than 10^297.
+	 */
+	Assert(e >= 0);
+	Assert(e <= 1650);
+	return (int32) ((((uint32) e) * 78913) >> 18);
+}
+
+/*  Returns floor(log_10(5^e)). */
+static inline int32
+log10Pow5(const int32 e)
+{
+	/*
+	 * The first value this approximation fails for is 5^2621 which is just
+	 * greater than 10^1832.
+	 */
+	Assert(e >= 0);
+	Assert(e <= 2620);
+	return (int32) ((((uint32) e) * 732923) >> 20);
+}
+
+static inline int
+copy_special_str(char *const result, const bool sign, const bool exponent, const bool mantissa)
+{
+	if (mantissa)
+	{
+		memcpy(result, "NaN", 3);
+		return 3;
+	}
+	if (sign)
+	{
+		result[0] = '-';
+	}
+	if (exponent)
+	{
+		memcpy(result + sign, "Infinity", 8);
+		return sign + 8;
+	}
+	result[sign] = '0';
+	return sign + 1;
+}
+
+static inline uint32
+float_to_bits(const float f)
+{
+	uint32		bits = 0;
+
+	memcpy(&bits, &f, sizeof(float));
+	return bits;
+}
+
+static inline uint64
+double_to_bits(const double d)
+{
+	uint64		bits = 0;
+
+	memcpy(&bits, &d, sizeof(double));
+	return bits;
+}
+
+#endif							/* RYU_COMMON_H */