File : fz_io.adb
1 ------------------------------------------------------------------------------
2 ------------------------------------------------------------------------------
3 -- This file is part of 'Finite Field Arithmetic', aka 'FFA'. --
4 -- --
5 -- (C) 2018 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 --
9 -- distribute this software ; Should you use this software for any purpose, --
10 -- or copy and distribute it to anyone or in any manner, you are breaking --
11 -- the laws of whatever soi-disant jurisdiction, and you promise to --
12 -- continue doing so for the indefinite future. In any case, please --
13 -- always : read and understand any software ; verify any PGP signatures --
14 -- that you use - for any purpose. --
15 -- --
16 -- See also http://trilema.com/2015/a-new-software-licensing-paradigm . --
17 ------------------------------------------------------------------------------
18 ------------------------------------------------------------------------------
19
20 with W_Pred; use W_Pred;
21 with W_Shifts; use W_Shifts;
22 with FZ_BitOp; use FZ_BitOp;
23 with FZ_Shift; use FZ_Shift;
24
25
26 package body FZ_IO is
27
28 -- Expand FZ N by nibble D, and determine whether this operation overflowed
29 procedure FZ_Insert_Bottom_Nibble(N : in out FZ;
30 D : in Nibble;
31 Overflow : out WBool) is
32
33 -- The overflow, if any, from shifting N in-place leftward by 4 bits
34 Shifted_N_Overflow : Word := 0;
35
36 begin
37 -- Make room in N for one additional hex digit (i.e. multiply N by 16)
38 FZ_ShiftLeft_O(N => N,
39 ShiftedN => N,
40 Count => 4,
41 Overflow => Shifted_N_Overflow);
42
43 -- Place the new digit into the now-vacated four bits at the bottom of N.
44 FZ_Or_W(N, D);
45
46 -- Record whether the above operation overflowed N:
47 Overflow := W_NZeroP(Shifted_N_Overflow);
48
49 end FZ_Insert_Bottom_Nibble;
50
51
52 -- Determine the number of ASCII characters required to represent N
53 function FZ_ASCII_Length(N : in FZ) return Char_Count is
54 begin
55 return N'Length * Nibbleness;
56 end FZ_ASCII_Length;
57
58
59 -- Write an ASCII hex representation of N into existing string buffer S
60 procedure FZ_To_Hex_String(N : in FZ; S : out String) is
61
62 -- Indices into the string S (note, String always indexes from 1)
63 subtype SiRange is Natural range S'First .. S'Last;
64
65 -- Position of current character in S being written
66 Si : SiRange; -- Walks from 1 to the string length of S
67
68 begin
69
70 -- Step through all indices of N, regardless of how it was indexed:
71 for i in 0 .. Word_Index(N'Length - 1) loop
72 declare
73
74 -- Index of current Word, walks from ~top~ Word of N to ~bottom~
75 Wi : constant Word_Index := N'Last - i;
76
77 -- Currently-selected Word of N
78 W : Word := N(Wi);
79
80 begin
81
82 -- For each nibble in the Word:
83 for j in 1 .. Nibbleness loop
84
85 -- Current position in S that is to be written
86 Si := (Natural(i) * Nibbleness) + j;
87
88 -- Rotate the top nibble of W into the bottom nibble.
89 W := Rotate_Left(W, 4);
90
91 -- Write the ASCII representation of the bottom nibble.
92 S(Si) := HexDigs(Natural(W and 16#F#));
93
94 end loop;
95
96 -- Barring cosmic ray, W will have rotated to its initial value
97 pragma Assert(W = N(Wi));
98
99 end;
100
101 end loop;
102
103 -- Barring cosmic ray, the last char written was to the final pos in S,
104 pragma Assert(Si = SiRange'Last); -- as S is mandatorily exactly-sized.
105
106 end FZ_To_Hex_String;
107
108 end FZ_IO;