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diff --git a/miniany/doc/www.bell-labs.com_usr_dmr_www_primevalC.txt b/miniany/doc/www.bell-labs.com_usr_dmr_www_primevalC.txt new file mode 100644 index 0000000..e7bcff2 --- /dev/null +++ b/miniany/doc/www.bell-labs.com_usr_dmr_www_primevalC.txt @@ -0,0 +1,188 @@ + 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. + + [new.gif] information: Warren Toomey, now at Bond University, has + managed to make one of the compilers (last1120c, see below) compile + itself using a First/Second edition Unix emulator for the PDP-11; see + his [1]ftp-available directory. More generally, it's worth looking into + the [2]PDP-11 Unix Preservation Society pages for sources and + simulators. + + As described in the [3]C History paper, 1972-73 were the truly + formative years in the development of the C language: this is when the + transition from typeless B to weakly typed C took place, mediated by + the (Neanderthal?) NB language, of which no source seems to survive. It + was also the period in which Unix was rewritten in C. + + In looking over this material, I have mixed emotions; so much of this + stuff is immature and not well-done, and there is an element of + embarrassment about displaying it. But at the same time it does capture + two moments in a period of creativeness and may have some historical + interest. + + Two tapes are present here; the first is labeled "last1120c", the + second "prestruct-c". I know from distant memory what these names mean: + the first is a saved copy of the compiler preserved just as we were + abandoning the PDP-11/20, which did not have multiply or divide + instructions, but instead a separate, optional unit that did these + operations (and also shifts) by storing the operands into memory + locations. (A [4]story about using this hardware is told elsewhere.) + + "prestruct-c" is a copy of the compiler just before I started changing + it to use structures itself. + + 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 . and -> for specifying members of a structure itself and + members of a pointed-to structure are both there. + + 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). These + would appear, though, by 5th or 6th edition Unix (say 1975), as + described (in Postscript) in the [5]C manual a couple of years after + these versions. + + Instead, pointer declarations were written in the style int ip[];. 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. + (Evolving compilers written in their own language are careful not to + take advantage of their own latest features.) + + It's interesting to note that the earlier compiler has a commented-out + preparation for a "long" keyword; the later one takes over its slot for + "struct." Implementation of long was a few years away. + + Aside from their small size, perhaps the most striking thing about + these programs is their primitive construction, particularly the many + constants strewn throughout; they are used for names of tokens, for + example. 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; in + the later, the start is simply taken to be 0. 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. (See the + [6]Unix History paper). In one of the files (prestruct-c/c10.c) the + kludgery is especially evident. + + Links to the source of the compilers are listed below. The files named + c0?.c are the first passes, which parse source and writes syntax trees + intermingled with some text on an intermediate file. The c1?.c files + are the code generators, which read the trees and generate code. The + format is straight text (with just NL characters separating lines; the + browsers I've tried cope with this). + + The code generation technique uses tables of instruction prototypes; a + parse tree is recursively matched against the part of the table + corresponding to its root operator. Restrictions on the types and + complexity of the operands can be expressed, and the table is searched + sequentially for the earliest matching fragment. Following each + restriction specification is the expansion specification; lower case + letters are literal, upper case things are replaced by things from the + operands in the tree. This is described in more detail in the paper + [7]A Tour through the PDP-11 Compiler. (This reference is troff source; + it can also be found in Postscript or PDF forms, though bundled with + other papers, under the [8]7th Edition Manual's home page). But do note + that this Tour describes the state of things after several years had + passed. + + There are four tables specifying how to compile an expression to a + register, to compile only for side effects, to compile only to test + condition codes, and to compile to push on the stack (used for function + arguments, or for temporaries). They were saved only with the + "last1120c" compiler; the tables for the later one would have been + similar. + + The source for the last1120c compiler also has a subsidiary table for + each pass with a bit of stuff that was not in the library, and some + encoding of facts about various operators as .s (assembler language) + files. + + Finally, there is the cvopt program, used to convert the nonce-language + expression template tables into assembler. With a lot of handwork, + there is probably enough material to construct a working version of the + last1120c compiler, where "works" means "turns source into PDP-11 + assembler." (See the [9]top of the page for one who succeeded.) + + The links for the files are: + + last1120c + + [10]c00.c + [11]c01.c + [12]c02.c + [13]c03.c + [14]c0t.s + [15]c10.c + [16]c11.c + [17]c1t.s + [18]regtab.s + [19]cctab.s + [20]sptab.s + [21]efftab.s + [22]cvopt.c + + prestruct-c + + [23]c00.c + [24]c01.c + [25]c02.c + [26]c03.c + [27]c10.c + [28]c11.c + +References + + 1. ftp://minnie.tuhs.org/pub/PDP-11/Sims/Apout/ + 2. http://minnie.tuhs.org/PUPS + 3. https://www.bell-labs.com/usr/dmr/www/chist.html + 4. https://www.bell-labs.com/usr/dmr/www/odd.html + 5. https://www.bell-labs.com/usr/dmr/www/cman.ps + 6. https://www.bell-labs.com/usr/dmr/www/hist.html + 7. http://plan9.bell-labs.com/7thEdMan/vol2/ctour.bun + 8. http://plan9.bell-labs.com/7thEdMan/index.html + 9. https://www.bell-labs.com/usr/dmr/www/primevalC.html#works + 10. https://www.bell-labs.com/usr/dmr/www/last1120c/c00.c + 11. https://www.bell-labs.com/usr/dmr/www/last1120c/c01.c + 12. https://www.bell-labs.com/usr/dmr/www/last1120c/c02.c + 13. https://www.bell-labs.com/usr/dmr/www/last1120c/c03.c + 14. https://www.bell-labs.com/usr/dmr/www/last1120c/c0t.s + 15. https://www.bell-labs.com/usr/dmr/www/last1120c/c10.c + 16. https://www.bell-labs.com/usr/dmr/www/last1120c/c11.c + 17. https://www.bell-labs.com/usr/dmr/www/last1120c/c1t.s + 18. https://www.bell-labs.com/usr/dmr/www/last1120c/regtab.s + 19. https://www.bell-labs.com/usr/dmr/www/last1120c/cctab.s + 20. https://www.bell-labs.com/usr/dmr/www/last1120c/sptab.s + 21. https://www.bell-labs.com/usr/dmr/www/last1120c/efftab.s + 22. https://www.bell-labs.com/usr/dmr/www/last1120c/cvopt.c + 23. https://www.bell-labs.com/usr/dmr/www/prestruct-c/c00.c + 24. https://www.bell-labs.com/usr/dmr/www/prestruct-c/c01.c + 25. https://www.bell-labs.com/usr/dmr/www/prestruct-c/c02.c + 26. https://www.bell-labs.com/usr/dmr/www/prestruct-c/c03.c + 27. https://www.bell-labs.com/usr/dmr/www/prestruct-c/c10.c + 28. https://www.bell-labs.com/usr/dmr/www/prestruct-c/c11.c |