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// Returns the number of decimal digits in v, which must not contain more than 9
22// digits.
23#[cfg_attr(feature = "no-panic", inline)]
24pub fn decimal_length9(v: u32) -> u32 {
25 // Function precondition: v is not a 10-digit number.
26 // (f2s: 9 digits are sufficient for round-tripping.)
27 debug_assert!(v < 1000000000);
28
29 if v >= 100000000 {
30 9
31 } else if v >= 10000000 {
32 8
33 } else if v >= 1000000 {
34 7
35 } else if v >= 100000 {
36 6
37 } else if v >= 10000 {
38 5
39 } else if v >= 1000 {
40 4
41 } else if v >= 100 {
42 3
43 } else if v >= 10 {
44 2
45 } else {
46 1
47 }
48}
49
50// Returns e == 0 ? 1 : [log_2(5^e)]; requires 0 <= e <= 3528.
51#[cfg_attr(feature = "no-panic", inline)]
52#[allow(dead_code)]
53pub fn log2_pow5(e: i32) -> i32 /* or u32 -> u32 */ {
54 // This approximation works up to the point that the multiplication
55 // overflows at e = 3529. If the multiplication were done in 64 bits, it
56 // would fail at 5^4004 which is just greater than 2^9297.
57 debug_assert!(e >= 0);
58 debug_assert!(e <= 3528);
59 ((e as u32 * 1217359) >> 19) as i32
60}
61
62// Returns e == 0 ? 1 : ceil(log_2(5^e)); requires 0 <= e <= 3528.
63#[cfg_attr(feature = "no-panic", inline)]
64pub fn pow5bits(e: i32) -> i32 /* or u32 -> u32 */ {
65 // This approximation works up to the point that the multiplication
66 // overflows at e = 3529. If the multiplication were done in 64 bits, it
67 // would fail at 5^4004 which is just greater than 2^9297.
68 debug_assert!(e >= 0);
69 debug_assert!(e <= 3528);
70 (((e as u32 * 1217359) >> 19) + 1) as i32
71}
72
73#[cfg_attr(feature = "no-panic", inline)]
74#[allow(dead_code)]
75pub fn ceil_log2_pow5(e: i32) -> i32 /* or u32 -> u32 */ {
76 log2_pow5(e) + 1
77}
78
79// Returns floor(log_10(2^e)); requires 0 <= e <= 1650.
80#[cfg_attr(feature = "no-panic", inline)]
81pub fn log10_pow2(e: i32) -> u32 /* or u32 -> u32 */ {
82 // The first value this approximation fails for is 2^1651 which is just greater than 10^297.
83 debug_assert!(e >= 0);
84 debug_assert!(e <= 1650);
85 (e as u32 * 78913) >> 18
86}
87
88// Returns floor(log_10(5^e)); requires 0 <= e <= 2620.
89#[cfg_attr(feature = "no-panic", inline)]
90pub fn log10_pow5(e: i32) -> u32 /* or u32 -> u32 */ {
91 // The first value this approximation fails for is 5^2621 which is just greater than 10^1832.
92 debug_assert!(e >= 0);
93 debug_assert!(e <= 2620);
94 (e as u32 * 732923) >> 20
95}
96