srpenndo@uokmax.UUCP (Sean Richard Penndorf) (11/01/88)
Our company is currently working on a BBS program for the Macintosh. We will be including XMODEM and YMODEM (and possibly ZMODEM and KERMIT) transfer protocols. However, I can't seem to get a working CRC-16 routine. We are working in Pascal, so I would prefer the routines in Pascal but will take C sources as well. Please, any help would be appreciated. Either a "byte-at-a-time" routine or a 256 Table routine would be great. If you have these sources OR you have information on where I can get these sources, please leave mail to srpenndo@uokmax.UUCP Thanks in advance. SIDE NOTE: If you have comments on what you would like to see (as a user or as a sysop) in a BBS program, you can mail your comments to the same address above. All comments welcome. Sean R. Penndorf Ultimatum Software
dick@venera.isi.edu (Richard Gillmann) (11/02/88)
Here is a version of the CRC calculation as used by XMODEM, YMODEM, etc.
It is written in Microsoft Pascal. The umulok routine is a library call
that does an unsigned multiply and allows overflow. It's used to
simulate a shift and check of the carry bit. Of course, this could be
much speeded up by writing in assembler or using tables.
{Computes a 16-bit circular redundancy check. Initialize your variable for
crc_value to 0, then call this routine for each byte.}
procedure crc_16(c : char; var crc_value : word);
begin
crc_value := crc_value xor (wrd(c)*256);
for var i := 1 to 8 do
if not umulok(crc_value,2,crc_value) then {hi bit was a 1}
crc_value := crc_value xor 16#1021; {X^15+X^12+X^5+1}
end {crc_16};beard@ux1.lbl.gov (Patrick C Beard) (11/08/88)
In article <6672@venera.isi.edu> dick@venera.isi.edu.UUCP (Richard Gillmann) writes: > >Here is a version of the CRC calculation as used by XMODEM, YMODEM, etc. >It is written in Microsoft Pascal. The umulok routine is a library call >that does an unsigned multiply and allows overflow. It's used to >simulate a shift and check of the carry bit. Of course, this could be >much speeded up by writing in assembler or using tables. > >{Computes a 16-bit circular redundancy check. Initialize your variable for > crc_value to 0, then call this routine for each byte.} >procedure crc_16(c : char; var crc_value : word); >begin > crc_value := crc_value xor (wrd(c)*256); > for var i := 1 to 8 do > if not umulok(crc_value,2,crc_value) then {hi bit was a 1} > crc_value := crc_value xor 16#1021; {X^15+X^12+X^5+1} >end {crc_16}; Here is a table driven version (in C, sorry). crc should be set to zero before using COMPUTE_CRC. /* crc.c -- routine for calculating a CRC-16. Put together by Patrick Beard, from Xmodem.3.6 distribution, by */ /* CRC-16 constants. From Usenet contribution by Mark G. Mendel, Network Systems Corp. (ihnp4!umn-cs!hyper!mark) */ /* the CRC polynomial. */ #define P 0x1021 /* number of bits in CRC */ #define W 16 /* the number of bits per char */ #define B 8 /* CRC-16 constant array... from Usenet contribution by Mark G. Mendel, Network Systems Corp. (ihnp4!umn-cs!hyper!mark) */ /* crctab as calculated by initcrctab() */ unsigned short crctab[1<<B] = { 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6, 0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d, 0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823, 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, 0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a, 0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70, 0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f, 0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e, 0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d, 0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634, 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3, 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a, 0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1, 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0 }; #define COMPUTE_CRC(crc,byte) \ crc = (crc<<B) ^ crctab[(crc>>(W-B)) ^ byte];