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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT LIBRARY COMPONENTS                          --

--                                                                          --

--       G N A T . S E C U R E _ H A S H E S . S H A 2 _ C O M M O N        --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--           Copyright (C) 2009, Free Software Foundation, Inc.             --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

package body GNAT.Secure_Hashes.SHA2_Common is

   ---------------

   -- Transform --

   ---------------

   procedure Transform

     (H_St : in out Hash_State.State;

      M_St : in out Message_State)

   is

      use System;

      subtype Word is Hash_State.Word;

      use type Hash_State.Word;

      function Ch (X, Y, Z : Word) return Word;

      function Maj (X, Y, Z : Word) return Word;

      pragma Inline (Ch, Maj);

      --  Elementary functions from FIPS PUB 180-3

      --------

      -- Ch --

      --------

      function Ch (X, Y, Z : Word) return Word is

      begin

         return (X and Y) xor ((not X) and Z);

      end Ch;

      ---------

      -- Maj --

      ---------

      function Maj (X, Y, Z : Word) return Word is

      begin

         return (X and Y) xor (X and Z) xor (Y and Z);

      end Maj;

      type Words is array (Natural range <>) of Word;

      X : Words (0 .. 15);

      for X'Address use M_St.Buffer'Address;

      pragma Import (Ada, X);

      W : Words (0 .. Rounds - 1);

      A, B, C, D, E, F, G, H, T1, T2 : Word;

   --  Start of processing for Transform

   begin

      if Default_Bit_Order /= High_Order_First then

         for J in X'Range loop

            Hash_State.Swap (X (J)'Address);

         end loop;

      end if;

      --  1. Prepare message schedule

      W (0 .. 15) := X;

      for T in 16 .. Rounds - 1 loop

         W (T) := S1 (W (T - 2)) + W (T - 7) + S0 (W (T - 15)) + W (T - 16);

      end loop;

      --  2. Initialize working variables

      A := H_St (0);

      B := H_St (1);

      C := H_St (2);

      D := H_St (3);

      E := H_St (4);

      F := H_St (5);

      G := H_St (6);

      H := H_St (7);

      --  3. Perform transformation rounds

      for T in 0 .. Rounds - 1 loop

         T1 := H + Sigma1 (E) + Ch (E, F, G) + K (T) + W (T);

         T2 := Sigma0 (A) + Maj (A, B, C);

         H := G;

         G := F;

         F := E;

         E := D + T1;

         D := C;

         C := B;

         B := A;

         A := T1 + T2;

      end loop;

      --  4. Update hash state

      H_St (0) := A + H_St (0);

      H_St (1) := B + H_St (1);

      H_St (2) := C + H_St (2);

      H_St (3) := D + H_St (3);

      H_St (4) := E + H_St (4);

      H_St (5) := F + H_St (5);

      H_St (6) := G + H_St (6);

      H_St (7) := H + H_St (7);

   end Transform;

end GNAT.Secure_Hashes.SHA2_Common;