Re: [TUHS] v7 source code for sh

[Will Senn <will.senn@gmail.com>]

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Thanks Bakul, that's interesting.

Impetus for the obfuscated c contest?! The same contest where a guy 
wrote a pdp11 emulator capable of running v0, v6, and 2.9bsd in 50 lines 
of c (Mills, 2018)? I still get a kick out of that code. Particularly 
because you can run Mullender's 1984 entry on the 2.9 bsd instance it 
hosts (it also works in v7, but it's too fast, even with stty 300).

Thankfully, macros, while adding an additional layer of complexity, 
aren't as impenetrable as the ioccc stuff:

    mills's prog.c snippet:
    struct timeval F,G; struct termios H,U={ T} ; enum{
    N=64,a=N<<7,b=a-1,c=a*32,d
    =c-1,    e=c/    2,f=    a*2,    g=a/2,h =g/2,j =h/ 2,Q=V*j*5} ;
    char*s=P,K,M;
    int*      p,      l[      a]      ,m,n,J,o=A,
    O=j,E,R,i,k,t,r,q,u,v,w,x,y,z
    ,B,C,    *D,Z    ;int    main    (){ for(D=mmap...

    mullender's mullender.c in it's entirety (requires v7 or better and
    pdp11):
    short main[] = {
         277, 04735, -4129, 25, 0, 477, 1019, 0xbef, 0, 12800,
         -113, 21119, 0x52d7, -1006, -7151, 0, 0x4bc, 020004,
         14880, 10541, 2056, 04010, 4548, 3044, -6716, 0x9,
         4407, 6, 5568, 1, -30460, 0, 0x9, 5570, 512, -30419,
         0x7e82, 0760, 6, 0, 4, 02400, 15, 0, 4, 1280, 4, 0,
         4, 0, 0, 0, 0x8, 0, 4, 0, ',', 0, 12, 0, 4, 0, '#',
         0, 020, 0, 4, 0, 30, 0, 026, 0, 0x6176, 120, 25712,
         'p', 072163, 'r', 29303, 29801, 'e'
    };

Later,

Will



On 2/19/22 10:06 AM, Bakul Shah wrote:
> https://research.swtch.com/shmacro
>
>> On Feb 19, 2022, at 7:44 AM, Will Senn <will.senn@gmail.com> wrote:
>>
>>  I have been poring through the v7 source code lately, and came 
>> across an oddity I would like to know more about. Specifically, in 
>> sh. The code for sh is c, but it makes *extensive* use of of macros, 
>> for example:
>>
>>     /usr/src/cmd/sh/word.c
>>     ...
>>     WHILE (c=nextc(0), space(c)) DONE
>>     ...
>>
>> The macros for sh are defined in mac.h:
>>
>>     /usr/src/cmd/sh/mac.h
>>     ...
>>     #define BEGIN   {
>>     #define END     }
>>     #define SWITCH  switch(
>>     #define IN      ){
>>     #define ENDSW   }
>>     #define FOR     for(
>>     #define WHILE   while(
>>     #define DO      ){
>>     #define OD      ;}
>>     #define REP     do{
>>     #define PER     }while(
>>     #define DONE    );
>>     ...
>>
>> I can read the resultant code through the lens of my experience 
>> coding c, but I'm curious why the macros and how this came about? In 
>> v6, the sh source is straight up c. Is there a story behind it worth 
>> knowing?
>>
>> Thanks,
>>
>> Will

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