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This archive contains a quick & dirty implementation of the IEEE Standard
1180-1990 accuracy test for inverse DCT.  It is not guaranteed to be
correct ... but if you find any bugs, please let me know (by email to

The test harness consists of the C program ieeetest.c and shell script
doieee.  For comparison purposes I have also supplied a copy of jrevdct.c,
the inverse DCT routine from release 4 of the Independent JPEG Group's
free JPEG software.  (jrevdct.c is slightly modified from the IJG release
so that it will compile without the IJG include files.)  jrevdct.c passes
the 1180 test --- or at least, this program thinks so.  jrevdct.out is
the output from a test run.

Note that numerical results may vary somewhat across machines.  This appears
to be mostly due to differing results from the cosine function.

  Check the Makefile, change CC and CFLAGS if needed.  Then say "make".
If your C compiler is non-ANSI, you may need to change includes and/or
function headers.

  To test a different IDCT routine, link with that routine instead of
jrevdct.o.  You will need to modify dct.h and/or ieeetest.c if your
routine's calling convention is not in-place modification of an array
of 64 "short"s.

  The standard test procedure is
        doieee ieeetest >outputfile
Expect it to take a while (almost 80 minutes on my old 68030 box).
Each of the six passes will emit a row of 100 dots as it runs.

You can grep the output for the word FAILS if you just want to know
yea or nay.

  I hereby release the test harness to the public domain.
                        Thomas G. Lane, 22 Nov 1993

IMPORTANT: jrevdct.c is NOT public domain, but is copyrighted free software
(not the same thing at all).  It is subject to IJG's distribution terms, which
primarily state that if you incorporate it into a program you must acknowledge
IJG's contribution in your program documentation.  For more details and the
complete IJG software, see the IJG FTP archive at, in directory

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