Watch this space.
a.out(V), UNIX Programmer's Manual First Edition, 3 November 1971.
UNIX historian and archivist.
Occasional Rust standard library contributor.
| Site | https://thalia.dev |
| GitHub | https://github.com/thaliaarchi |
Thalia Archibald
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Computer science PhD student at the University of Utah, researching compiler verification with @regehr.
UNIX historian and archivist.
Occasional Rust standard library contributor.
UNIX historian and archivist.
Occasional Rust standard library contributor.
This snippet deliberately triggers a "Bus error -- Core dumped":
int o1[];
o1 = -3;
*o1;
From Dennis_Tapes/dmr/cgd/cg1.c:expr.
Another strange pattern from the same program.
This one reassigns the address of an array, `int nlist[250]`, in char increments. Arrays are no longer lvalues, so this doesn't work anymore. Also, the address is unaligned every other iteration.
lbp;
nlist[250];
getnam()
{
extern nlist, lbp;
char nlist[], lbp[], c;
loop:
c = *lbp++;
if (c==';' | c=='\n')
goto el;
*nlist++ = c;
goto loop;
el:
*nlist++ = '\0';
}
Somewhat simplified from Dennis_Tapes/dmr/cgd/cg1.c:getnam.
This snippet appears in cvft, a compiler for translating Fortran threaded code to machine code from June 1972, which is notably derived from the early C code generator. See putchar (and also getcha) in dmr/cgd/cvft.c.
The earliest extant C compiler is last1120c from July 1972, the last C version for the PDP-11/20, before they migrated to the PDP-11/45. This version still has the label lvalue behavior of B seen in cvft. Then, it was changed to the modern behavior by the time of prestruct-c from December 1972. That version supports structures, but does not yet use them itself.
All three can be found in Dennis_Tapes: https://www.tuhs.org/Archive/Applications/Dennis_Tapes
At the time, C was rapidly evolving into what we recognize today.
It started as B, an untyped and interpreted language that only had one kind of value, a word. This was a perfect fit for the PDP-7 that UNIX started on, with 18-bit words, but as they transitioned to the PDP-11, with 16-bit words and 8-bit addressing, this became a limitation.
Soon, types were added, to distinguish char, int, and pointers, and it became known as NB ("New B"). But, B wasn't particularly fast, as it was interpreted (well, threaded).
Once it was rewritten to be compiled, the language became known as C (perhaps initially as NC). For a short while, everything in C was an lvalue like B, giving the above snippet, but this was dropped a few months later, presumably for efficiency.
Some UNIX utilities had been written in B/C from the start, but efforts to rewrite the kernel itself in B/C had failed. Finally, once structs were added to C, it was powerful enough to support the kernel and it was rewritten in C over the summer of 1973, culminating in the release of UNIX V4.
A cursed feature of C in 1972: Labels and functions were reassignable (i.e., lvalues)!
For example, this is a clever way to initialize once:
goto init;
init:
ouptr = oubuf;
init = init1;
init1:
which is compiled to:
jmp *4120
mov 4136,4144
mov 4122,4120
Note the indirect jump and assignment to that address. All gotos used indirect jumps. This apparently would have also worked with functions.
Happy Star Trek day!
In the original Star Trek pilot, the ship printed the distress call on paper—a technology dropped in the rest of the franchise. In 1965, computing was on paper, so even this printer was futuristic, with laser sounds instead of loud impact printing. This clip also shows a video intercom.
Star Trek: The Original Series S1E11 “The Menagerie, Part I” (34:11) and pilot “The Cage”
#retrocomputing #vintagecomputing #startrek #computingincinema
My talk at VCF PNW yesterday went well! Thanks for all the great questions.
Recording forthcoming.
