[1471] | 1 | #include "mit-copyright.h" |
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[1090] | 2 | #include <sys/file.h> |
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| 3 | #include <sys/types.h> |
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| 4 | #include <sys/stat.h> |
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| 5 | #include <netinet/in.h> |
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[1075] | 6 | |
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| 7 | /* I N _ C K S U M |
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| 8 | * |
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| 9 | * Checksum routine for Internet Protocol family headers (C Version). |
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[1471] | 10 | * NOTE: this code is taken from 4.3bsd ping, and modified to read a file. |
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[1075] | 11 | * |
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| 12 | */ |
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[1090] | 13 | unsigned |
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[1075] | 14 | in_cksum( filename, statp) char *filename; struct stat *statp; |
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| 15 | { |
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| 16 | int fd; |
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| 17 | struct stat statbuf; |
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| 18 | static char buf[ 8192]; |
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| 19 | register int nleft; |
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| 20 | register u_short *w; |
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| 21 | register unsigned int sum = 0; |
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| 22 | unsigned int carry = 0; |
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| 23 | |
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| 24 | fd = open( filename, O_RDONLY); |
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| 25 | |
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| 26 | /* get the file's optimal blocksize: |
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| 27 | * we want to call read() as little as possible, |
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| 28 | * because each call spills the register variables. |
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| 29 | */ |
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| 30 | if ( ! statp) { |
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| 31 | statp = &statbuf; |
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| 32 | fstat( fd, statp); |
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| 33 | } |
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| 34 | /* |
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| 35 | * Our algorithm is simple, using a 48 bit accumulator (sum), |
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| 36 | * we add sequential 16 bit words to it, and at the end, fold |
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| 37 | * back all the carry bits from the top 32 bits into the lower |
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| 38 | * 16 bits. |
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| 39 | * this means we can handle files containing 2**32 16-bit words, |
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| 40 | * that is, 2**33 bytes, which is a little more than 8 gigabytes. |
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| 41 | */ |
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| 42 | while ( 0 < ( nleft = read( fd, buf, (*statp).st_blksize))) { |
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| 43 | w = (u_short *) buf; |
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| 44 | while( nleft > 1 ) { |
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| 45 | sum += *w++; |
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| 46 | nleft -= 2; |
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| 47 | } |
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| 48 | |
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| 49 | /* mop up an odd byte, if necessary */ |
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[1090] | 50 | if( nleft == 1 ) { |
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| 51 | ((u_char *)w)[ 1] = '\0'; |
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| 52 | sum += *w; |
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| 53 | } |
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[1075] | 54 | carry += sum >> 16; |
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| 55 | sum &= 0xffff; |
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| 56 | } |
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| 57 | close( fd); |
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| 58 | |
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| 59 | /* |
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| 60 | * add back carry's top 16 bits and low 16 bits. |
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| 61 | * this makes this checksum byte-order independent. |
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| 62 | */ |
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| 63 | sum = sum + (carry >> 16) + (carry & 0xffff); |
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| 64 | sum += (sum >> 16); /* add resulting carry */ |
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[1090] | 65 | return( htons( 0xffff & ~sum)); /* discard last carry. */ |
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[1075] | 66 | /* the ~ (one's complement) isn't really necessary here; |
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| 67 | * it makes a nonzero checksum for a file of zeroes, |
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| 68 | * which is useful for network applications of this algorithm. |
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| 69 | */ |
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| 70 | } |
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