-- (c) William Welch 2004
--
-- This software is provided 'as-is', without any express or implied 
-- warranty. In no event will the authors be held liable for any damages 
-- arising from the use of this software.
--
-- Permission is granted to anyone to use this software for any purpose, 
-- including commercial applications, and to alter it and redistribute it 
-- freely, subject to the following restrictions:
--
-- 1. The origin of this software must not be misrepresented; 
--    you must not claim that you wrote the original software. 
--    If you use this software in a product, an acknowledgment in 
--    the product documentation would be appreciated but is not required.
--
-- 2. Altered source versions must be plainly marked as such, and must 
--    not be misrepresented as being the original software.
--
-- 3. This notice may not be removed or altered from any source distribution.
--
-- This license is commonly known as the zlib/libpng License.
--
-- icmp.jal bvwelch 19 may 2004
-- revised 18 march 2005
-- See RFC 792 for details

function icmp_is_echo return bit is
  if (MemRdEx(ip_off , 9) != 1) | (MemRd(icmp_off) != 8) then
    return false
  end if
  return true
end function

procedure icmp_echo_reply is
  var byte n, sum_hi, sum_lo, cnt_hi, cnt_lo

  -- echo reply opcode is 0
  MemWr(icmp_off, 0)

  -- do icmp checksum
  -- note byte swap
  I16_SVL ( IP_LEN , cnt_lo , cnt_hi)
  I16_LDL ( L16 , cnt_hi , cnt_lo )
  I16_SUB8 ( L16, ip_hdrsize )
  I16_SVL ( L16 , cnt_hi , cnt_lo)
  chksum_write(icmp_off, 0, 2, cnt_hi , cnt_lo)

  -- swap IP src and dest
  ip_swap_addr

  -- now do the IP chksum
  n = ( MemRd(ip_off) & 0x0F ) << 2
  chksum_write(ip_off, 0, 10, 0, n)

  -- swap ethernet source and dest
  net_swap_addr

  -- now send pkt
  -- note byte swap
  I16_SVL ( IP_LEN , cnt_lo , cnt_hi)
  I16_LDL ( L16 , cnt_hi , cnt_lo )
  I16_ADD8 ( L16, 14 )
  I16_SVL ( L16 , cnt_hi , cnt_lo)
  net_txpkt(cnt_hi , cnt_lo)
end procedure