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      --
   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 Word_Ops; use Word_Ops;
  21 
  22 
  23 package body FZ_Basic is
  24    
  25    ---------------------------------------------------------------------------
  26    -- Fundamental Operations on FZ (finite integers)
  27    ---------------------------------------------------------------------------
  28    
  29    -- Determine the Bitness of N
  30    function FZ_Bitness(N : in FZ) return Bit_Count is
  31    begin
  32       return N'Length * Words.Bitness;
  33    end FZ_Bitness;
  34    
  35    
  36    -- Determine the Bitness of the given FZ's Length
  37    function FZ_Bitness_Log2(N : in FZ) return Positive is
  38       W : Bit_Count := N'Length;
  39       R : Positive  := 1;
  40    begin
  41       while W > 1 loop
  42          W := W / 2;
  43          R := R + 1;
  44       end loop;
  45       return R - 1;
  46    end FZ_Bitness_Log2;
  47    
  48    
  49    -- N := 0
  50    procedure FZ_Clear(N : out FZ) is
  51    begin
  52       N := (others => 0);
  53    end FZ_Clear;
  54    
  55    
  56    -- Set given FZ to a given truth value
  57    procedure WBool_To_FZ(V : in WBool; N : out FZ) is
  58    begin
  59       FZ_Clear(N);
  60       FZ_Set_Head(N, V);
  61    end WBool_To_FZ;
  62    
  63    
  64    -- First word of N := Source
  65    procedure FZ_Set_Head(N : out FZ; Source : in Word) is
  66    begin
  67       N(N'First) := Source;
  68    end FZ_Set_Head;
  69    
  70    
  71    -- First word of N
  72    function FZ_Get_Head(N : in FZ) return Word is
  73    begin
  74       return N(N'First);
  75    end FZ_Get_Head;
  76    
  77    
  78    -- Exchange X and Y
  79    procedure FZ_Swap(X : in out FZ; Y : in out FZ) is
  80       T : FZ(X'Range);
  81    begin
  82       T := X;
  83       X := Y;
  84       Y := T;
  85    end FZ_Swap;
  86    
  87    
  88    -- Constant-time MUX: Sel = 0: Result := X; Sel = 1: Result := Y
  89    procedure FZ_Mux(X : in FZ; Y : in FZ; Result : out FZ; Sel : in WBool) is
  90    begin
  91       for i in X'Range loop
  92          Result(i) := W_Mux(X(i), Y(i), Sel);
  93       end loop;
  94    end FZ_Mux;
  95    
  96 end FZ_Basic;