1 /*---------------------------------------------------------------------------
2  *
3  * Common routines for Ryu floating-point output.
4  *
5  * Portions Copyright (c) 2018-2020, PostgreSQL Global Development Group
6  *
7  * IDENTIFICATION
8  *	  src/common/ryu_common.h
9  *
10  * This is a modification of code taken from github.com/ulfjack/ryu under the
11  * terms of the Boost license (not the Apache license). The original copyright
12  * notice follows:
13  *
14  * Copyright 2018 Ulf Adams
15  *
16  * The contents of this file may be used under the terms of the Apache
17  * License, Version 2.0.
18  *
19  *     (See accompanying file LICENSE-Apache or copy at
20  *      http://www.apache.org/licenses/LICENSE-2.0)
21  *
22  * Alternatively, the contents of this file may be used under the terms of the
23  * Boost Software License, Version 1.0.
24  *
25  *     (See accompanying file LICENSE-Boost or copy at
26  *      https://www.boost.org/LICENSE_1_0.txt)
27  *
28  * Unless required by applicable law or agreed to in writing, this software is
29  * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
30  * KIND, either express or implied.
31  *
32  *---------------------------------------------------------------------------
33  */
34 #ifndef RYU_COMMON_H
35 #define RYU_COMMON_H
36 
37 /*
38  * Upstream Ryu's output is always the shortest possible. But we adjust that
39  * slightly to improve portability: we avoid outputting the exact midpoint
40  * value between two representable floats, since that relies on the reader
41  * getting the round-to-even rule correct, which seems to be the common
42  * failure mode.
43  *
44  * Defining this to 1 would restore the upstream behavior.
45  */
46 #define STRICTLY_SHORTEST 0
47 
48 #if SIZEOF_SIZE_T < 8
49 #define RYU_32_BIT_PLATFORM
50 #endif
51 
52 /*  Returns e == 0 ? 1 : ceil(log_2(5^e)). */
53 static inline uint32
54 pow5bits(const int32 e)
55 {
56 	/*
57 	 * This approximation works up to the point that the multiplication
58 	 * overflows at e = 3529.
59 	 *
60 	 * If the multiplication were done in 64 bits, it would fail at 5^4004
61 	 * which is just greater than 2^9297.
62 	 */
63 	Assert(e >= 0);
64 	Assert(e <= 3528);
65 	return ((((uint32) e) * 1217359) >> 19) + 1;
66 }
67 
68 /*  Returns floor(log_10(2^e)). */
69 static inline int32
70 log10Pow2(const int32 e)
71 {
72 	/*
73 	 * The first value this approximation fails for is 2^1651 which is just
74 	 * greater than 10^297.
75 	 */
76 	Assert(e >= 0);
77 	Assert(e <= 1650);
78 	return (int32) ((((uint32) e) * 78913) >> 18);
79 }
80 
81 /*  Returns floor(log_10(5^e)). */
82 static inline int32
83 log10Pow5(const int32 e)
84 {
85 	/*
86 	 * The first value this approximation fails for is 5^2621 which is just
87 	 * greater than 10^1832.
88 	 */
89 	Assert(e >= 0);
90 	Assert(e <= 2620);
91 	return (int32) ((((uint32) e) * 732923) >> 20);
92 }
93 
94 static inline int
95 copy_special_str(char *const result, const bool sign, const bool exponent, const bool mantissa)
96 {
97 	if (mantissa)
98 	{
99 		memcpy(result, "NaN", 3);
100 		return 3;
101 	}
102 	if (sign)
103 	{
104 		result[0] = '-';
105 	}
106 	if (exponent)
107 	{
108 		memcpy(result + sign, "Infinity", 8);
109 		return sign + 8;
110 	}
111 	result[sign] = '0';
112 	return sign + 1;
113 }
114 
115 static inline uint32
116 float_to_bits(const float f)
117 {
118 	uint32		bits = 0;
119 
120 	memcpy(&bits, &f, sizeof(float));
121 	return bits;
122 }
123 
124 static inline uint64
125 double_to_bits(const double d)
126 {
127 	uint64		bits = 0;
128 
129 	memcpy(&bits, &d, sizeof(double));
130 	return bits;
131 }
132 
133 #endif							/* RYU_COMMON_H */
134