1 // Translated from C to Rust. The original C code can be found at
2 // https://github.com/ulfjack/ryu and carries the following license:
3 //
4 // Copyright 2018 Ulf Adams
5 //
6 // The contents of this file may be used under the terms of the Apache License,
7 // Version 2.0.
8 //
9 // (See accompanying file LICENSE-Apache or copy at
10 // http://www.apache.org/licenses/LICENSE-2.0)
11 //
12 // Alternatively, the contents of this file may be used under the terms of
13 // the Boost Software License, Version 1.0.
14 // (See accompanying file LICENSE-Boost or copy at
15 // https://www.boost.org/LICENSE_1_0.txt)
16 //
17 // Unless required by applicable law or agreed to in writing, this software
18 // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
19 // KIND, either express or implied.
20
21 use crate::common::pow5bits;
22
23 pub static DOUBLE_POW5_INV_SPLIT2: [(u64, u64); 15] = [
24 (1, 2305843009213693952),
25 (5955668970331000884, 1784059615882449851),
26 (8982663654677661702, 1380349269358112757),
27 (7286864317269821294, 2135987035920910082),
28 (7005857020398200553, 1652639921975621497),
29 (17965325103354776697, 1278668206209430417),
30 (8928596168509315048, 1978643211784836272),
31 (10075671573058298858, 1530901034580419511),
32 (597001226353042382, 1184477304306571148),
33 (1527430471115325346, 1832889850782397517),
34 (12533209867169019542, 1418129833677084982),
35 (5577825024675947042, 2194449627517475473),
36 (11006974540203867551, 1697873161311732311),
37 (10313493231639821582, 1313665730009899186),
38 (12701016819766672773, 2032799256770390445),
39 ];
40
41 pub static POW5_INV_OFFSETS: [u32; 19] = [
42 0x54544554, 0x04055545, 0x10041000, 0x00400414, 0x40010000, 0x41155555, 0x00000454, 0x00010044,
43 0x40000000, 0x44000041, 0x50454450, 0x55550054, 0x51655554, 0x40004000, 0x01000001, 0x00010500,
44 0x51515411, 0x05555554, 0x00000000,
45 ];
46
47 pub static DOUBLE_POW5_SPLIT2: [(u64, u64); 13] = [
48 (0, 1152921504606846976),
49 (0, 1490116119384765625),
50 (1032610780636961552, 1925929944387235853),
51 (7910200175544436838, 1244603055572228341),
52 (16941905809032713930, 1608611746708759036),
53 (13024893955298202172, 2079081953128979843),
54 (6607496772837067824, 1343575221513417750),
55 (17332926989895652603, 1736530273035216783),
56 (13037379183483547984, 2244412773384604712),
57 (1605989338741628675, 1450417759929778918),
58 (9630225068416591280, 1874621017369538693),
59 (665883850346957067, 1211445438634777304),
60 (14931890668723713708, 1565756531257009982),
61 ];
62
63 pub static POW5_OFFSETS: [u32; 21] = [
64 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x40000000, 0x59695995, 0x55545555, 0x56555515,
65 0x41150504, 0x40555410, 0x44555145, 0x44504540, 0x45555550, 0x40004000, 0x96440440, 0x55565565,
66 0x54454045, 0x40154151, 0x55559155, 0x51405555, 0x00000105,
67 ];
68
69 pub static DOUBLE_POW5_TABLE: [u64; 26] = [
70 1,
71 5,
72 25,
73 125,
74 625,
75 3125,
76 15625,
77 78125,
78 390625,
79 1953125,
80 9765625,
81 48828125,
82 244140625,
83 1220703125,
84 6103515625,
85 30517578125,
86 152587890625,
87 762939453125,
88 3814697265625,
89 19073486328125,
90 95367431640625,
91 476837158203125,
92 2384185791015625,
93 11920928955078125,
94 59604644775390625,
95 298023223876953125,
96 ];
97
98 // Computes 5^i in the form required by Ryū.
99 #[cfg_attr(feature = "no-panic", inline)]
compute_pow5(i: u32) -> (u64, u64)100 pub unsafe fn compute_pow5(i: u32) -> (u64, u64) {
101 let base = i / DOUBLE_POW5_TABLE.len() as u32;
102 let base2 = base * DOUBLE_POW5_TABLE.len() as u32;
103 let offset = i - base2;
104 debug_assert!(base < DOUBLE_POW5_SPLIT2.len() as u32);
105 let mul = *DOUBLE_POW5_SPLIT2.get_unchecked(base as usize);
106 if offset == 0 {
107 return mul;
108 }
109 debug_assert!(offset < DOUBLE_POW5_TABLE.len() as u32);
110 let m = *DOUBLE_POW5_TABLE.get_unchecked(offset as usize);
111 let b0 = m as u128 * mul.0 as u128;
112 let b2 = m as u128 * mul.1 as u128;
113 let delta = pow5bits(i as i32) - pow5bits(base2 as i32);
114 debug_assert!(i / 16 < POW5_OFFSETS.len() as u32);
115 let shifted_sum = (b0 >> delta)
116 + (b2 << (64 - delta))
117 + ((*POW5_OFFSETS.get_unchecked((i / 16) as usize) >> ((i % 16) << 1)) & 3) as u128;
118 (shifted_sum as u64, (shifted_sum >> 64) as u64)
119 }
120
121 // Computes 5^-i in the form required by Ryū.
122 #[cfg_attr(feature = "no-panic", inline)]
compute_inv_pow5(i: u32) -> (u64, u64)123 pub unsafe fn compute_inv_pow5(i: u32) -> (u64, u64) {
124 let base = (i + DOUBLE_POW5_TABLE.len() as u32 - 1) / DOUBLE_POW5_TABLE.len() as u32;
125 let base2 = base * DOUBLE_POW5_TABLE.len() as u32;
126 let offset = base2 - i;
127 debug_assert!(base < DOUBLE_POW5_INV_SPLIT2.len() as u32);
128 let mul = *DOUBLE_POW5_INV_SPLIT2.get_unchecked(base as usize); // 1/5^base2
129 if offset == 0 {
130 return mul;
131 }
132 debug_assert!(offset < DOUBLE_POW5_TABLE.len() as u32);
133 let m = *DOUBLE_POW5_TABLE.get_unchecked(offset as usize); // 5^offset
134 let b0 = m as u128 * (mul.0 - 1) as u128;
135 let b2 = m as u128 * mul.1 as u128; // 1/5^base2 * 5^offset = 1/5^(base2-offset) = 1/5^i
136 let delta = pow5bits(base2 as i32) - pow5bits(i as i32);
137 debug_assert!(base < POW5_INV_OFFSETS.len() as u32);
138 let shifted_sum = ((b0 >> delta) + (b2 << (64 - delta)))
139 + 1
140 + ((*POW5_INV_OFFSETS.get_unchecked((i / 16) as usize) >> ((i % 16) << 1)) & 3) as u128;
141 (shifted_sum as u64, (shifted_sum >> 64) as u64)
142 }
143