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1 | // Copyright 2015 The Rust Project Developers. See the COPYRIGHT |
2 | // file at the top-level directory of this distribution and at | |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
11 | //! Extended precision "soft float", for internal use only. | |
12 | ||
cc61c64b | 13 | // This module is only for dec2flt and flt2dec, and only public because of coretests. |
b039eaaf SL |
14 | // It is not intended to ever be stabilized. |
15 | #![doc(hidden)] | |
16 | #![unstable(feature = "core_private_diy_float", | |
17 | reason = "internal routines only exposed for testing", | |
18 | issue = "0")] | |
19 | ||
20 | /// A custom 64-bit floating point type, representing `f * 2^e`. | |
21 | #[derive(Copy, Clone, Debug)] | |
22 | #[doc(hidden)] | |
23 | pub struct Fp { | |
24 | /// The integer mantissa. | |
25 | pub f: u64, | |
26 | /// The exponent in base 2. | |
27 | pub e: i16, | |
28 | } | |
29 | ||
30 | impl Fp { | |
31 | /// Returns a correctly rounded product of itself and `other`. | |
32 | pub fn mul(&self, other: &Fp) -> Fp { | |
33 | const MASK: u64 = 0xffffffff; | |
34 | let a = self.f >> 32; | |
35 | let b = self.f & MASK; | |
36 | let c = other.f >> 32; | |
37 | let d = other.f & MASK; | |
38 | let ac = a * c; | |
39 | let bc = b * c; | |
40 | let ad = a * d; | |
41 | let bd = b * d; | |
42 | let tmp = (bd >> 32) + (ad & MASK) + (bc & MASK) + (1 << 31) /* round */; | |
43 | let f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); | |
44 | let e = self.e + other.e + 64; | |
45 | Fp { f: f, e: e } | |
46 | } | |
47 | ||
48 | /// Normalizes itself so that the resulting mantissa is at least `2^63`. | |
49 | pub fn normalize(&self) -> Fp { | |
50 | let mut f = self.f; | |
51 | let mut e = self.e; | |
c30ab7b3 SL |
52 | if f >> (64 - 32) == 0 { |
53 | f <<= 32; | |
54 | e -= 32; | |
55 | } | |
56 | if f >> (64 - 16) == 0 { | |
57 | f <<= 16; | |
58 | e -= 16; | |
59 | } | |
60 | if f >> (64 - 8) == 0 { | |
61 | f <<= 8; | |
62 | e -= 8; | |
63 | } | |
64 | if f >> (64 - 4) == 0 { | |
65 | f <<= 4; | |
66 | e -= 4; | |
67 | } | |
68 | if f >> (64 - 2) == 0 { | |
69 | f <<= 2; | |
70 | e -= 2; | |
71 | } | |
72 | if f >> (64 - 1) == 0 { | |
73 | f <<= 1; | |
74 | e -= 1; | |
75 | } | |
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76 | debug_assert!(f >= (1 >> 63)); |
77 | Fp { f: f, e: e } | |
78 | } | |
79 | ||
80 | /// Normalizes itself to have the shared exponent. | |
81 | /// It can only decrease the exponent (and thus increase the mantissa). | |
82 | pub fn normalize_to(&self, e: i16) -> Fp { | |
83 | let edelta = self.e - e; | |
84 | assert!(edelta >= 0); | |
85 | let edelta = edelta as usize; | |
86 | assert_eq!(self.f << edelta >> edelta, self.f); | |
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87 | Fp { |
88 | f: self.f << edelta, | |
89 | e: e, | |
90 | } | |
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91 | } |
92 | } |