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author | Michael Brown | 2006-07-20 01:38:05 +0200 |
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committer | Michael Brown | 2006-07-20 01:38:05 +0200 |
commit | 2c0eb6eb1dc2b3828adad19ff46aeffae95b0102 (patch) | |
tree | 37de4267c2cf9d1df9fd233de0dab9b7fa57df4d /src/net/tcpip_if.c | |
parent | udp_open() takes ports in network-endian order. (diff) | |
download | ipxe-2c0eb6eb1dc2b3828adad19ff46aeffae95b0102.tar.gz ipxe-2c0eb6eb1dc2b3828adad19ff46aeffae95b0102.tar.xz ipxe-2c0eb6eb1dc2b3828adad19ff46aeffae95b0102.zip |
Correct TCP/IP checksum generation.
Diffstat (limited to 'src/net/tcpip_if.c')
-rw-r--r-- | src/net/tcpip_if.c | 65 |
1 files changed, 50 insertions, 15 deletions
diff --git a/src/net/tcpip_if.c b/src/net/tcpip_if.c index 80d69268..98d64804 100644 --- a/src/net/tcpip_if.c +++ b/src/net/tcpip_if.c @@ -105,21 +105,56 @@ int trans_tx ( struct pk_buff *pkb, struct tcpip_protocol *tcpip, } /** - * Calculate internet checksum + * Calculate continued TCP/IP checkum * - * @v b Pointer to the data - * @v len Length of data to be checksummed - * @ret result 16 bit internet checksum + * @v partial Checksum of already-summed data, in network byte order + * @v data Data buffer + * @v len Length of data buffer + * @ret cksum Updated checksum, in network byte order + * + * Calculates a TCP/IP-style 16-bit checksum over the data block. The + * checksum is returned in network byte order. + * + * This function may be used to add new data to an existing checksum. + * The function assumes that both the old data and the new data start + * on even byte offsets; if this is not the case then you will need to + * byte-swap either the input partial checksum, the output checksum, + * or both. Deciding which to swap is left as an exercise for the + * interested reader. + */ +unsigned int tcpip_continue_chksum ( unsigned int partial, const void *data, + size_t len ) { + unsigned int cksum = ( ( ~partial ) & 0xffff ); + unsigned int value; + unsigned int i; + + for ( i = 0 ; i < len ; i++ ) { + value = * ( ( uint8_t * ) data + i ); + if ( i & 1 ) { + /* Odd bytes: swap on little-endian systems */ + value = be16_to_cpu ( value ); + } else { + /* Even bytes: swap on big-endian systems */ + value = le16_to_cpu ( value ); + } + cksum += value; + if ( cksum > 0xffff ) + cksum -= 0xffff; + } + + return ( ( ~cksum ) & 0xffff ); +} + +/** + * Calculate TCP/IP checkum + * + * @v data Data buffer + * @v len Length of data buffer + * @ret cksum Checksum, in network byte order + * + * Calculates a TCP/IP-style 16-bit checksum over the data block. The + * checksum is returned in network byte order. */ -uint16_t calc_chksum(void *b, int len) { - uint16_t *buf = b, result; - uint16_t sum=0; - for ( sum = 0; len > 1; len -= 2 ) /* Sum all 16b words */ - sum += *buf++; - if ( len == 1 ) /* If any stray bytes, */ - sum += *(unsigned char*)buf; /* add to sum */ - sum = (sum >> 16) + (sum & 0xffff); /* Add the carry */ - sum += (sum >> 16); /* (again) */ - result = ~sum; /* Take the one's complement */ - return result; /* Return 16b value */ +unsigned int tcpip_chksum ( const void *data, size_t len ) { + return tcpip_continue_chksum ( 0xffff, data, len ); } |