File : fz_barr.ads
1 ------------------------------------------------------------------------------
2 ------------------------------------------------------------------------------
3 -- This file is part of 'Finite Field Arithmetic', aka 'FFA'. --
4 -- --
5 -- (C) 2019 Stanislav Datskovskiy ( www.loper-os.org ) --
6 -- http://wot.deedbot.org/17215D118B7239507FAFED98B98228A001ABFFC7.html --
7 -- --
8 -- You do not have, nor can you ever acquire the right to use, copy or --
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14 -- that you use - for any purpose. --
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16 -- See also http://trilema.com/2015/a-new-software-licensing-paradigm . --
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18 ------------------------------------------------------------------------------
19
20 with Words; use Words;
21 with FZ_Type; use FZ_Type;
22
23
24 package FZ_Barr is
25
26 pragma Pure;
27
28 -- Precomputed data for Barrett's Modular Reduction
29 type Barretoid(ZXMLength : Indices;
30 BarretoidLength : Indices) is
31 record
32 ZXM : FZ(1 .. ZXMLength); -- Zero-Extended Modulus
33 J : FZBit_Index; -- Jm
34 B : FZ(1 .. BarretoidLength); -- The Barrettoid itself
35 ZSlide : FZBit_Index; -- Amount to slide Z
36 Degenerate : WBool; -- Is it degenerate case?
37 end record;
38
39
40 -- Prepare the precomputed Barrettoid corresponding to a given Modulus
41 procedure FZ_Make_Barrettoid(Modulus : in FZ;
42 Result : out Barretoid)
43 with Pre => Result.B'Length = 2 * Modulus'Length and
44 Result.ZXM'Length = Modulus'Length + 1;
45
46
47 -- Reduce N using the given precomputed Barrettoid.
48 procedure FZ_Barrett_Reduce(X : in FZ;
49 Bar : in Barretoid;
50 XReduced : in out FZ);
51 pragma Inline_Always(FZ_Barrett_Reduce);
52
53 end FZ_Barr;