www.cs.bell-labs.com/~dmr/primevalC.html -> www.cs.bell-labs.com/who/dmr/primevalC.html
Very early C compilers and language Several years ago, Paul Vixie and Keith Bostic found a DECtape drive, attached it to a VAX, and offered to read old DECtapes. Even at the time, this was an antiquarian pursuit, and it presented an opportunity to mine beneath the raised floor of the computer room and unearth some of the DECtapes we'd stored since the early 1970s. Gradually, I've been curating some of this, and here offer some of the artifacts. Unfortunately existing tapes lack interesting things like earliest Unix OS source, but some indicative fossils have been prepared for exhibition.
It's a bit hard to get really accurate dates for these compilers, except that they are certainly 1972-73. There are date bits on the tape image, but they suffer from a possible off-by-a-year error because we changed epochs more than once during this era, and also because the files may have been copied or fiddled after they were the source for the compiler in contemporaneous use. The earlier compiler does not know about structures at all: the string "struct" does not appear anywhere. The second tape has a compiler that does implement structures in a way that begins to approach their current meaning. Their declaration syntax seems to use () instead of {}, but . Neither compiler yet handled the general declaration syntax of today or even K&R I, with its compound declarators like the one in int **ipp; The compilers have not yet evolved the notion of compounding of type constructors ("array of pointers to functions", for example).
A fossil from this era survives even in modern C, where the notation can be used in declarations of arguments. On the other hand, the later of the two does accept the * notation, even though it doesn't use it. Aside from their small size, perhaps the most striking thing about these programs is their primitive construction, particularly the many constants strewn throughout; This is because the preprocessor didn't exist at the time. A second, less noticeable, but astonishing peculiarity is the space allocation: temporary storage is allocated that deliberately overwrites the beginning of the program, smashing its initialization code to save space. The two compilers differ in the details in how they cope with this. In the earlier one, the start is found by naming a function; This indicates that the first compiler was written before we had a machine with memory mapping, so the origin of the program was not at location 0, whereas by the time of the second, we had a PDP-11 that did provide mapping.
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