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////////////////////////////////////////////////////////////////////////////////

//

// Filename:    ipsum.c

//

// Project:     OpenArty, an entirely open SoC based upon the Arty platform

//

// Purpose:     To calculate (and return) an IP checksum on a section of data.

//              The data must be contiguous in memory, and the checksum field

//      (which is usually a part of it) must be blank when calling this

//      function.

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

////////////////////////////////////////////////////////////////////////////////

//

// Copyright (C) 2015-2016, Gisselquist Technology, LLC

//

// This program is free software (firmware): you can redistribute it and/or

// modify it under the terms of  the GNU General Public License as published

// by the Free Software Foundation, either version 3 of the License, or (at

// your option) any later version.

//

// This program is distributed in the hope that it will be useful, but WITHOUT

// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or

// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

// for more details.

//

// You should have received a copy of the GNU General Public License along

// with this program.  (It's in the $(ROOT)/doc directory, run make with no

// target there if the PDF file isn't present.)  If not, see

// <http://www.gnu.org/licenses/> for a copy.

//

// License:     GPL, v3, as defined and found on www.gnu.org,

//              http://www.gnu.org/licenses/gpl.html

//

//

////////////////////////////////////////////////////////////////////////////////

//

//

#include "zipcpu.h"

#include "ipcksum.h"

#define ASM

unsigned        ipcksum(int len, unsigned *ptr) {

#ifndef ASM

        unsigned        checksum = 0;

        for(int i=0; i<len; i++)

                checksum = checksum + (ptr[i] & 0x0ffff) + (ptr[i] >> 16);

        while(checksum & ~0x0ffff)

                checksum = (checksum & 0x0ffff) + (checksum >> 16);

        return checksum ^ 0x0ffff;

#else

asm(ASMFNSTR("ipcksum")                 // R1 = length (W), R2 = packet pointer

        "\tMOV  R1,R3\n"                // R3 is now the remaining length

        "\tCLR  R1\n"                   // R1 will be our checksum accumulator

".Lloop:\n"

        "\tLW   (R2),R4\n"

        "\tADD  R4,R1\n"

        "\tADD.C        1,R1\n"

        "\tADD  4,R2\n"

        "\tSUB  1,R3\n"

        "\tBZ   .Lexit\n"

        "\tBRA  .Lloop\n"

".Lexit:\n"

        "\tMOV  R1,R3\n"

        "\tAND  0x0ffff,R1\n"

        "\tLSR  16,R3\n"

        "\tADD  R3,R1\n"

        "\tTEST 0xffff0000,R1\n"        // The carry bit can only and will only

        "\tADD.NZ 1,R1\n"               // ever be a one here.  Add it in.

        "\tAND  0x0ffff,R1\n"

        "\tXOR  0x0ffff,R1\n"

        "\tRETN");

#endif

}