As it seems from other posts, the story is not completely true;
there was indeed such an error somewhere sometime with NASA,
but the error that destroyed the Mariner spacecraft was different (a
missing hyphen on
a hand-written variable specification, which had not been translated
correctly to computer code).
I believe that there are similar pitfalls in other languages, too,
although FORTRAN is very special,
because it allows spaces even in the middle of identifiers (and
numbers), such as
DO 3 I = 1 . 10
which in every other programming language would disqualify as an
assignment statement
because of the spaces around the DO symbol.
My favorite PL/1 example from a real world program is this:
IF 9 < ZZ < 20 THEN DO; ...
someone with a math background obviously coded this :-)
the expectation was, that the statement be executed if ZZ is in the
range 10 to 19.
Unfortunately, this is translated by PL/1 as follows:
IF (9 < ZZ) < 20 THEN DO;
9 < ZZ is a result of type BIT(1) and yields '0'B or '1'B, depending on ZZ;
this result is converted to decimal, so that it can be compared to the
decimal constant 20
and the result therefore is ALWAYS FALSE.
This is clearly not what the coder had intended.
We detected this luckily, using a site-written PL/1 diagnosing tool,
which complained because of the
implied type conversion (BIT(1) to decimal). About 2 percent of the
total PL/1 code base
had similar logic errors, which were undetected before we scanned all
the source codes with our
new tool in 2007. After that, we changed the deployment processes, so
that the new tool
runs with every software deployment.
Kind regards
Bernd
Am 29.03.2022 um 17:03 schrieb David Spiegel:
Hi gil,
I remember reading the article approximately 40 years ago.
It was in Datamation, which was an IT magazine.
You've never heard of Datamation before? ... How many years have you
been in this business?
The story was related to an unmanned spaceship (i.e. Venus Probe)
whose trajectory was calculated by a FORTRAN program
with the following statements:
DO 3 I=1.3
.
.
3
Since there was a period between "1" and "3" (instead of a comma), the
loop ran precisely once
and assigned 1.3 to DO3I (FORTRAN removes blanks before compile) a
variable which is automatically declared REAL, because its first letter
is outside the INTEGER Range I-N.
Here is another reference (not Datamation) (which does not mention the
financial loss)
Please see:
IEEE Xplore Full-Text PDF:
<https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4392951>
Page 58
Regards,
David
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