raw
ffa_ch5_egypt.kv        1 ------------------------------------------------------------------------------
ffa_ch5_egypt.kv        2 ------------------------------------------------------------------------------
ffa_ch5_egypt.kv        3 -- This file is part of 'Finite Field Arithmetic', aka 'FFA'.               --
ffa_ch5_egypt.kv        4 --                                                                          --
ffa_ch5_egypt.kv        5 -- (C) 2017 Stanislav Datskovskiy ( www.loper-os.org )                      --
ffa_ch5_egypt.kv        6 -- http://wot.deedbot.org/17215D118B7239507FAFED98B98228A001ABFFC7.html     --
ffa_ch5_egypt.kv        7 --                                                                          --
ffa_ch5_egypt.kv        8 -- You do not have, nor can you ever acquire the right to use, copy or      --
ffa_ch5_egypt.kv        9 -- distribute this software ; Should you use this software for any purpose, --
ffa_ch5_egypt.kv       10 -- or copy and distribute it to anyone or in any manner, you are breaking   --
ffa_ch5_egypt.kv       11 -- the laws of whatever soi-disant jurisdiction, and you promise to         --
ffa_ch5_egypt.kv       12 -- continue doing so for the indefinite future. In any case, please         --
ffa_ch5_egypt.kv       13 -- always : read and understand any software ; verify any PGP signatures    --
ffa_ch5_egypt.kv       14 -- that you use - for any purpose.                                          --
ffa_ch5_egypt.kv       15 --                                                                          --
ffa_ch5_egypt.kv       16 -- See also http://trilema.com/2015/a-new-software-licensing-paradigm .     --
ffa_ch5_egypt.kv       17 ------------------------------------------------------------------------------
ffa_ch5_egypt.kv       18 ------------------------------------------------------------------------------
ffa_ch5_egypt.kv       19 
ffa_ch5_egypt.kv       20 with Words;    use Words;
ffa_ch5_egypt.kv       21 with FZ_Basic; use FZ_Basic;
ffa_ch5_egypt.kv       22 with FZ_Pred;  use FZ_Pred;
ffa_ch5_egypt.kv       23 with FZ_Arith; use FZ_Arith;
ffa_ch5_egypt.kv       24 with FZ_Shift; use FZ_Shift;
ffa_ch5_egypt.kv       25 
ffa_ch5_egypt.kv       26 
ffa_ch5_egypt.kv       27 package body FZ_Mul is
ffa_ch5_egypt.kv       28    
ffa_ch5_egypt.kv       29    -- 'Egyptological' multiplier. XY_Lo and XY_Hi hold result of X*Y.
ffa_ch5_egypt.kv       30    procedure FZ_Mul_Egyptian(X     : in  FZ;
ffa_ch5_egypt.kv       31                              Y     : in  FZ;
ffa_ch5_egypt.kv       32                              XY_Lo : out FZ;
ffa_ch5_egypt.kv       33                              XY_Hi : out FZ) is
ffa_ch5_egypt.kv       34       
ffa_ch5_egypt.kv       35       -- Register holding running product
ffa_ch5_egypt.kv       36       XY : FZ(1 .. X'Length + Y'Length);
ffa_ch5_egypt.kv       37       
ffa_ch5_egypt.kv       38       -- X-Slide
ffa_ch5_egypt.kv       39       XS : FZ(1 .. X'Length + Y'Length);
ffa_ch5_egypt.kv       40       
ffa_ch5_egypt.kv       41       -- Y-Slide
ffa_ch5_egypt.kv       42       YS : FZ(Y'Range) := Y;
ffa_ch5_egypt.kv       43       
ffa_ch5_egypt.kv       44    begin
ffa_ch5_egypt.kv       45       -- Product register begins empty
ffa_ch5_egypt.kv       46       FZ_Clear(XY);
ffa_ch5_egypt.kv       47       
ffa_ch5_egypt.kv       48       -- X-Slide initially equals X:
ffa_ch5_egypt.kv       49       XS(1            .. X'Length) := X;
ffa_ch5_egypt.kv       50       XS(X'Length + 1 .. XS'Last)  := (others => 0);
ffa_ch5_egypt.kv       51       
ffa_ch5_egypt.kv       52       -- For each bit of Y:
ffa_ch5_egypt.kv       53       for i in 1 .. FZ_Bitness(Y) loop
ffa_ch5_egypt.kv       54          
ffa_ch5_egypt.kv       55          -- If lowest bit of Y-Slide is 1, X-Slide is added into XY
ffa_ch5_egypt.kv       56          FZ_Add_Gated(X    => XY, Y => XS, Sum => XY,
ffa_ch5_egypt.kv       57                       Gate => FZ_OddP(YS));
ffa_ch5_egypt.kv       58          
ffa_ch5_egypt.kv       59          -- X-Slide := X-Slide * 2
ffa_ch5_egypt.kv       60          FZ_ShiftLeft(XS, XS, 1);
ffa_ch5_egypt.kv       61          
ffa_ch5_egypt.kv       62          -- Y-Slide := Y-Slide / 2
ffa_ch5_egypt.kv       63          FZ_ShiftRight(YS, YS, 1);
ffa_ch5_egypt.kv       64          
ffa_ch5_egypt.kv       65       end loop;
ffa_ch5_egypt.kv       66       
ffa_ch5_egypt.kv       67       -- Write out the Product's lower and upper FZs:
ffa_ch5_egypt.kv       68       XY_Lo := XY(1                .. XY_Lo'Length);
ffa_ch5_egypt.kv       69       XY_Hi := XY(XY_Lo'Length + 1 .. XY'Last);
ffa_ch5_egypt.kv       70       
ffa_ch5_egypt.kv       71    end FZ_Mul_Egyptian;
ffa_ch5_egypt.kv       72    pragma Inline_Always(FZ_Mul_Egyptian);
ffa_ch5_egypt.kv       73 
ffa_ch5_egypt.kv       74 end FZ_Mul;