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-- This file is part of 'Finite Field Arithmetic', aka 'FFA'.               --
--                                                                          --
-- (C) 2019 Stanislav Datskovskiy ( www.loper-os.org )                      --
-- http://wot.deedbot.org/17215D118B7239507FAFED98B98228A001ABFFC7.html     --
--                                                                          --
-- You do not have, nor can you ever acquire the right to use, copy or      --
-- distribute this software ; Should you use this software for any purpose, --
-- or copy and distribute it to anyone or in any manner, you are breaking   --
-- the laws of whatever soi-disant jurisdiction, and you promise to         --
-- continue doing so for the indefinite future. In any case, please         --
-- always : read and understand any software ; verify any PGP signatures    --
-- that you use - for any purpose.                                          --
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-- See also http://trilema.com/2015/a-new-software-licensing-paradigm .     --
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with FZ_Type; use FZ_Type;


-- "Low Multiplication" computes only the bottom half of the product XY.
-- Presently, it is used solely in Barrett's Modular Reduction.

package FZ_LoMul is
   
   pragma Pure;
   
   -- Threshhold for Low Mul - at or below this many Words, we use Comba mult.
   Low_Mul_Thresh : constant Indices := 8;
   
   -- Multiply. (CAUTION: UNBUFFERED)
   procedure FZ_Low_Multiply_Unbuffered(X     : in  FZ;
                                        Y     : in  FZ;
                                        XY    : out FZ);
   pragma Inline_Always(FZ_Low_Multiply_Unbuffered);
   
   -- Comba's multiplier. (CAUTION: UNBUFFERED)
   procedure FZ_Low_Mul_Comba(X     : in  FZ;
                              Y     : in  FZ;
                              XY    : out FZ);
   pragma Inline_Always(FZ_Low_Mul_Comba);
   
   -- Low Multiplier. (CAUTION: UNBUFFERED)
   procedure Low_Mul(X  : in  FZ;
                     Y  : in  FZ;
                     XY : out FZ)
     with Pre => X'Length = Y'Length and
     XY'Length = X'Length and
     X'Length mod 2 = 0;
   -- CAUTION: Inlining prohibited for Low_Mul !
   
   -- Low-Only Multiplier. Preserves the inputs.
   procedure FZ_Low_Multiply_Buffered(X     : in  FZ;
                                      Y     : in  FZ;
                                      XY    : out FZ)
     with Pre => X'Length = Y'Length and
     XY'Length = X'Length and
     X'Length mod 2 = 0;
   
end FZ_LoMul;