perm filename SRCCHK[3,2] blob sn#363323 filedate 1978-06-27 generic text, type T, neo UTF8
SRCCHK is a different flavor of  SRCCOM  (SouRCe  COMpare,  i.e.
line-by-line  comparison of text files) based on hashing of full
text lines.  It does not ignore past column 80 like SRCCOM does.
On  the  other hand, it does not attempt to identify the context
of insertions and deletions like SRCCOM does; which is a FEATURE
not  a  deficiency,  it  avoids getting all confused.  The major
uses of SRCCHK are:  (1) after moving a lot of text around in  a
file,  to  see  if  any text as been lost or duplicated, without
being concerned with where text got  moved  to;  (2)  to  get  a
quick-and-dirty  estimate  of  file  changes  after  SRCCOM went
bezerk due to too many pieces of text moved around or  too  much
correlation  between different pages causing mis-match; (3) in a
file that has lines identical through  column  80  but  possibly
different  beyond,  to  see the changes, where SRCCOM claims the
lines aren't changed.   For further discussion, HELP SRCCOM. See
also BINCOM.

N.b., the hashing of strings (i.e. lines of text) is done by the
perturbed-linear-congruential method, just as in  POX.  Although
hashing  conflicts (two nonequal strings with equal 35-bit hash)
have been constructed artificially,  the  chance  of  a  hashing
conflict  in  a  natural file is quite low (the hash numbers are
pseudo-random, expected number of conflicts equals 2↑(-35) times
N*(N-1)/2 where N is the number of different lines in the file).