---

---

 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;