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ffa_ch9_exodus.kv       1 ------------------------------------------------------------------------------
ffa_ch9_exodus.kv       2 ------------------------------------------------------------------------------
ffa_ch9_exodus.kv       3 -- This file is part of 'Finite Field Arithmetic', aka 'FFA'.               --
ffa_ch9_exodus.kv       4 --                                                                          --
ffa_ch9_exodus.kv       5 -- (C) 2018 Stanislav Datskovskiy ( www.loper-os.org )                      --
ffa_ch9_exodus.kv       6 -- http://wot.deedbot.org/17215D118B7239507FAFED98B98228A001ABFFC7.html     --
ffa_ch9_exodus.kv       7 --                                                                          --
ffa_ch9_exodus.kv       8 -- You do not have, nor can you ever acquire the right to use, copy or      --
ffa_ch9_exodus.kv       9 -- distribute this software ; Should you use this software for any purpose, --
ffa_ch9_exodus.kv      10 -- or copy and distribute it to anyone or in any manner, you are breaking   --
ffa_ch9_exodus.kv      11 -- the laws of whatever soi-disant jurisdiction, and you promise to         --
ffa_ch9_exodus.kv      12 -- continue doing so for the indefinite future. In any case, please         --
ffa_ch9_exodus.kv      13 -- always : read and understand any software ; verify any PGP signatures    --
ffa_ch9_exodus.kv      14 -- that you use - for any purpose.                                          --
ffa_ch9_exodus.kv      15 --                                                                          --
ffa_ch9_exodus.kv      16 -- See also http://trilema.com/2015/a-new-software-licensing-paradigm .     --
ffa_ch9_exodus.kv      17 ------------------------------------------------------------------------------
ffa_ch9_exodus.kv      18 ------------------------------------------------------------------------------
ffa_ch9_exodus.kv      19 
ffa_ch9_exodus.kv      20 with W_Shifts; use W_Shifts;
ffa_ch9_exodus.kv      21 
ffa_ch9_exodus.kv      22 
ffa_ch9_exodus.kv      23 package body W_Mul is
ffa_ch9_exodus.kv      24    
ffa_ch9_exodus.kv      25    -- Multiply half-words X and Y, producing a Word-sized product
ffa_ch9_exodus.kv      26    function Mul_HalfWord(X : in HalfWord; Y : in HalfWord) return Word is
ffa_ch9_exodus.kv      27       
ffa_ch9_exodus.kv      28       -- X-Slide
ffa_ch9_exodus.kv      29       XS : Word := X;
ffa_ch9_exodus.kv      30       
ffa_ch9_exodus.kv      31       -- Y-Slide
ffa_ch9_exodus.kv      32       YS : Word := Y;
ffa_ch9_exodus.kv      33       
ffa_ch9_exodus.kv      34       -- Gate Mask
ffa_ch9_exodus.kv      35       GM : Word;
ffa_ch9_exodus.kv      36       
ffa_ch9_exodus.kv      37       -- The Product
ffa_ch9_exodus.kv      38       XY : Word := 0;
ffa_ch9_exodus.kv      39       
ffa_ch9_exodus.kv      40       -- Performed for each bit of HalfWord's bitness:
ffa_ch9_exodus.kv      41       procedure Bit is
ffa_ch9_exodus.kv      42       begin
ffa_ch9_exodus.kv      43          
ffa_ch9_exodus.kv      44          -- Compute the gate mask
ffa_ch9_exodus.kv      45          GM := 0 - (YS and 1);
ffa_ch9_exodus.kv      46          
ffa_ch9_exodus.kv      47          -- Perform the gated addition
ffa_ch9_exodus.kv      48          XY := XY + (XS and GM);
ffa_ch9_exodus.kv      49          
ffa_ch9_exodus.kv      50          -- Crank the next Y-slide bit into position
ffa_ch9_exodus.kv      51          YS := Shift_Right(YS, 1);
ffa_ch9_exodus.kv      52          
ffa_ch9_exodus.kv      53          -- Advance the X-slide by 1 bit
ffa_ch9_exodus.kv      54          XS := Shift_Left(XS, 1);
ffa_ch9_exodus.kv      55          
ffa_ch9_exodus.kv      56       end Bit;
ffa_ch9_exodus.kv      57       pragma Inline_Always(Bit);
ffa_ch9_exodus.kv      58       
ffa_ch9_exodus.kv      59    begin
ffa_ch9_exodus.kv      60       
ffa_ch9_exodus.kv      61       -- For each bit of the Y-Slide (unrolled) :
ffa_ch9_exodus.kv      62       for b in 1 .. HalfByteness loop
ffa_ch9_exodus.kv      63          
ffa_ch9_exodus.kv      64          Bit; Bit; Bit; Bit; Bit; Bit; Bit; Bit;
ffa_ch9_exodus.kv      65          
ffa_ch9_exodus.kv      66       end loop;
ffa_ch9_exodus.kv      67       
ffa_ch9_exodus.kv      68       -- Return the Product
ffa_ch9_exodus.kv      69       return XY;
ffa_ch9_exodus.kv      70       
ffa_ch9_exodus.kv      71    end Mul_HalfWord;
ffa_ch9_exodus.kv      72    pragma Inline_Always(Mul_HalfWord);
ffa_ch9_exodus.kv      73    
ffa_ch9_exodus.kv      74    
ffa_ch9_exodus.kv      75    -- Get the bottom half of a Word
ffa_ch9_exodus.kv      76    function BottomHW(W : in Word) return HalfWord is
ffa_ch9_exodus.kv      77    begin
ffa_ch9_exodus.kv      78       return W and (2**HalfBitness - 1);
ffa_ch9_exodus.kv      79    end BottomHW;
ffa_ch9_exodus.kv      80    pragma Inline_Always(BottomHW);
ffa_ch9_exodus.kv      81    
ffa_ch9_exodus.kv      82    
ffa_ch9_exodus.kv      83    -- Get the top half of a Word
ffa_ch9_exodus.kv      84    function TopHW(W : in Word) return HalfWord is
ffa_ch9_exodus.kv      85    begin
ffa_ch9_exodus.kv      86       return Shift_Right(W, HalfBitness);
ffa_ch9_exodus.kv      87    end TopHW;
ffa_ch9_exodus.kv      88    pragma Inline_Always(TopHW);
ffa_ch9_exodus.kv      89    
ffa_ch9_exodus.kv      90    
ffa_ch9_exodus.kv      91    -- Carry out X*Y mult, return lower word XY_LW and upper word XY_HW.
ffa_ch9_exodus.kv      92    procedure Mul_Word(X       : in  Word;
ffa_ch9_exodus.kv      93                       Y       : in  Word;
ffa_ch9_exodus.kv      94                       XY_LW   : out Word;
ffa_ch9_exodus.kv      95                       XY_HW   : out Word) is
ffa_ch9_exodus.kv      96       
ffa_ch9_exodus.kv      97       -- Bottom half of multiplicand X
ffa_ch9_exodus.kv      98       XL : constant HalfWord := BottomHW(X);
ffa_ch9_exodus.kv      99       
ffa_ch9_exodus.kv     100       -- Top half of multiplicand X
ffa_ch9_exodus.kv     101       XH : constant HalfWord := TopHW(X);
ffa_ch9_exodus.kv     102       
ffa_ch9_exodus.kv     103       -- Bottom half of multiplicand Y
ffa_ch9_exodus.kv     104       YL : constant HalfWord := BottomHW(Y);
ffa_ch9_exodus.kv     105       
ffa_ch9_exodus.kv     106       -- Top half of multiplicand Y
ffa_ch9_exodus.kv     107       YH : constant HalfWord := TopHW(Y);
ffa_ch9_exodus.kv     108       
ffa_ch9_exodus.kv     109       -- XL * YL
ffa_ch9_exodus.kv     110       LL : constant Word := Mul_HalfWord(XL, YL);
ffa_ch9_exodus.kv     111       
ffa_ch9_exodus.kv     112       -- XL * YH
ffa_ch9_exodus.kv     113       LH : constant Word := Mul_HalfWord(XL, YH);
ffa_ch9_exodus.kv     114       
ffa_ch9_exodus.kv     115       -- XH * YL
ffa_ch9_exodus.kv     116       HL : constant Word := Mul_HalfWord(XH, YL);
ffa_ch9_exodus.kv     117       
ffa_ch9_exodus.kv     118       -- XH * YH
ffa_ch9_exodus.kv     119       HH : constant Word := Mul_HalfWord(XH, YH);
ffa_ch9_exodus.kv     120       
ffa_ch9_exodus.kv     121       -- Carry
ffa_ch9_exodus.kv     122       CL : constant Word := TopHW(TopHW(LL) + BottomHW(LH) + BottomHW(HL));
ffa_ch9_exodus.kv     123       
ffa_ch9_exodus.kv     124    begin
ffa_ch9_exodus.kv     125       
ffa_ch9_exodus.kv     126       -- Get the bottom half of the Product:
ffa_ch9_exodus.kv     127       XY_LW := LL + Shift_Left(LH + HL, HalfBitness);
ffa_ch9_exodus.kv     128       
ffa_ch9_exodus.kv     129       -- Get the top half of the Product:
ffa_ch9_exodus.kv     130       XY_HW := HH + TopHW(HL) + TopHW(LH) + CL;
ffa_ch9_exodus.kv     131       
ffa_ch9_exodus.kv     132    end Mul_Word;
ffa_ch9_exodus.kv     133    pragma Inline_Always(Mul_Word);
ffa_ch9_exodus.kv     134    
ffa_ch9_exodus.kv     135 end W_Mul;