WSJT-X/lib/fst4/get_crc24.f90
2020-07-23 12:48:50 -05:00

26 lines
665 B
Fortran

subroutine get_crc24(mc,len,ncrc)
!
! 1. To calculate 24-bit CRC, mc(1:len-24) is the message and mc(len-23:len) are zero.
! 2. To check a received CRC, mc(1:len) is the received message plus CRC.
! ncrc will be zero if the received message/CRC are consistent.
!
character c24*24
integer*1 mc(len)
integer*1 r(25),p(25)
integer ncrc
! polynomial for 24-bit CRC 0x100065b
data p/1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,0,0,1,0,1,1,0,1,1/
! divide by polynomial
r=mc(1:25)
do i=0,len-25
r(25)=mc(i+25)
r=mod(r+r(1)*p,2)
r=cshift(r,1)
enddo
write(c24,'(24b1)') r(1:24)
read(c24,'(b24.24)') ncrc
end subroutine get_crc24