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::*;
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