malachite_float/conversion/string/
from_string.rs

1// Copyright © 2025 Mikhail Hogrefe
2//
3// This file is part of Malachite.
4//
5// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
6// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
7// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.
8
9use crate::Float;
10use alloc::string::{String, ToString};
11use core::str::FromStr;
12use malachite_base::num::basic::traits::{Infinity, NaN, NegativeInfinity, NegativeZero, Zero};
13use malachite_base::num::conversion::string::options::FromSciStringOptions;
14use malachite_base::num::conversion::traits::{FromSciString, FromStringBase};
15use malachite_base::rounding_modes::RoundingMode::*;
16use malachite_q::Rational;
17
18fn reduce_exponent_in_hex_string(s: &str) -> Option<(String, i32)> {
19    if let Some(exp_index) = s.find('E') {
20        let tail = &s[exp_index + 1..];
21        let hash_index = tail.find('#').unwrap();
22        let tail = &tail[..hash_index];
23        let original_exponent = i32::from_str(tail).unwrap();
24        if original_exponent.unsigned_abs() < 20 {
25            return None;
26        }
27        let mut new_s = s[..=exp_index].to_string();
28        new_s += "+20";
29        new_s += &s[exp_index + hash_index + 1..];
30        Some((new_s, (original_exponent << 2) - 80))
31    } else {
32        None
33    }
34}
35
36fn from_hex_string(s: &str) -> Float {
37    match s {
38        "NaN" => Float::NAN,
39        "Infinity" => Float::INFINITY,
40        "-Infinity" => Float::NEGATIVE_INFINITY,
41        "0x0.0" => Float::ZERO,
42        "-0x0.0" => Float::NEGATIVE_ZERO,
43        s => {
44            let (s, sign) = if let Some(s) = s.strip_prefix('-') {
45                (s, false)
46            } else {
47                (s, true)
48            };
49            let s = s.strip_prefix("0x").unwrap();
50            let hash_index = s.find('#').unwrap();
51            let precision = u64::from_str(&s[hash_index + 1..]).unwrap();
52            let mut options = FromSciStringOptions::default();
53            options.set_base(16);
54            let x = if let Some((alt_s, exp_offset)) = reduce_exponent_in_hex_string(s) {
55                let hash_index = alt_s.find('#').unwrap();
56                Float::from_rational_prec_round(
57                    Rational::from_sci_string_with_options(&alt_s[..hash_index], options).unwrap(),
58                    precision,
59                    Exact,
60                )
61                .0 << exp_offset
62            } else {
63                Float::from_rational_prec_round(
64                    Rational::from_sci_string_with_options(&s[..hash_index], options).unwrap(),
65                    precision,
66                    Exact,
67                )
68                .0
69            };
70            if sign { x } else { -x }
71        }
72    }
73}
74
75impl FromStringBase for Float {
76    fn from_string_base(base: u8, s: &str) -> Option<Self> {
77        assert_eq!(base, 16);
78        Some(from_hex_string(s))
79    }
80}
malachite_float/conversion/string/from_string.rs

malachite_float/conversion/string/
from_string.rs
