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The time now is Fri 24 May 2013, 02:32
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 Forum index » Off-Topic Area » Programming
unsorted C macros for small/fast static apps
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technosaurus


Joined: 18 May 2008
Posts: 3843
PostPosted: Thu 06 Dec 2012, 00:33    Post subject:  
just need to figure out how to deal with blah-0041.2 and blah-041.1
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Ibidem

Joined: 25 May 2010
Posts: 248
PostPosted: Thu 06 Dec 2012, 19:24    Post subject:  
technosaurus wrote:
just need to figure out how to deal with blah-0041.2 and blah-041.1

If you look in the manpage, that isn't ambiguous: numbers starting with 0 are considered to have an implied decimal point before the first 0, so the more leading zeros, the smaller.
Since it diverges at 00 vs 04, anything after the decimal point is ignored.

But there is another bug in the version I just posted:
compare 2004 204, and my code assumes it's dealing with a leading 0 Embarassed
I have an idea for fixing it, but haven't done so yet.
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technosaurus


Joined: 18 May 2008
Posts: 3843
PostPosted: Wed 30 Jan 2013, 03:58    Post subject:  
simple qsort example, takes all arguments and prints sorted tab separated list
Code:
#include <string.h>

static inline int cmp(const void *a, const void *b){
   return strcmp(*(const char **)a, *(const char **)b);
}

int main(int argc, char *argv[]){
    qsort(++argv, --argc, sizeof(char *), cmp);
    while (argc){
      write(1,argv[0],strlen(argv[0]));
      write(1,(--argc && argv++)?"\t":"\n",1);
   }
}

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technosaurus


Joined: 18 May 2008
Posts: 3843
PostPosted: Thu 07 Feb 2013, 00:07    Post subject:  
a faster (but bigger) strlen -needs work (misses \0 on multiples of Cool

Code:
size_t strlen(char *s){
size_t *v,ret;
v=(size_t  *)s;
while (!(~((((*v & 0x7F7F7F7F) + 0x7F7F7F7F) | *v) | 0x7F7F7F7F))) v++; /*64bit size_t?*/
ret=(char *)v-s;
while (s[++ret]);
return ret;
}


notes: need to use an unsigned int or 0 is 111111111111.....
maybe use:
((*v>>24)&&(*v&0xFF00FFFF))&&((*v&0xFFFF00FF)&&(*v<<24))
because the compiler can combine some of these operations and/or thread them
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technosaurus


Joined: 18 May 2008
Posts: 3843
PostPosted: Sat 16 Feb 2013, 18:04    Post subject:  
here is a one-liner to generate macros for 300+ syscalls
Code:
grep __NR_ unistd_32.h |awk '
{print "#define " substr($2,6,length($2)) "(...) syscall(" $2 ", __VA_ARGS__ )"}
' | sort > syscalls.h

and now you have a 0kb c "library"

Note: zero-arg functions like fork() may need to be modified on older compilers and all of the types (structs, etc...) will need to be defined and there is absolutely no type checking. If you would like some semblance of type checking, you can later modify the defines to be static inline functions like:

Code:
static inline long mycall(int a, char *b, struct somestruct c){
return syscall(__NR_mycall, a, b, c);
}


There are quite a few other functions in the kernel that would be useful if you wanted to wrap them in a syscall for userspace (all of the crypto stuff and filesystem detection for instance)
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technosaurus


Joined: 18 May 2008
Posts: 3843
PostPosted: Sun 17 Feb 2013, 23:20    Post subject:  
still working on syscalls. Here is a wacked out macro that redefines syscall() based on the number of args.
Code:
#define NARGS(...) NARGS_(__VA_ARGS__, 6, 5, 4, 3, 2, 1, 0)(__VA_ARGS__)
#define NARGS_(dummy, n1, n2, n3, n4, n5, n6, n, ...) syscall##n
#define syscall(...) NARGS(__VA_ARGS__)

thus syscall(__NR_mycall) becomes syscall0(mycall)
while syscall(__NR_mycall,a,b,c,d,e,f) becomes syscall6(mycall,a,b,c,d,e,f)

... and you thought you needed c++ for this Smile
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technosaurus


Joined: 18 May 2008
Posts: 3843
PostPosted: Mon 04 Mar 2013, 01:27    Post subject:  
here is a good link to some try-catch macros
http://www.di.unipi.it/~nids/docs/longjump_try_trow_catch.html
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