Brainfuck interpreter in C

This is my bare-bones Brainfuck interpreter in C using lots of unixisms. What improvements can I make (with respect to the clarity of code, or obvious features to add)?

```
#include
#include
#include
#include
#include
#include
#include
#include
#include

void error(char *msg) {
fprintf(stderr, "Error: %s\n", msg);
}

enum { MEMSIZE = 30000 };

//unsigned char *mem;
unsigned char mem[MEMSIZE];
unsigned char *ptr;
unsigned char *prog;
size_t progsize;

int init(char *progname) {
int f,r;
struct stat fs;
ptr = mem;// = calloc(MEMSIZE, 1);
f = open(progname, O_RDONLY);
assert(f != -1);
r = fstat(f, &fs);
assert(r == 0);
prog = mmap(NULL, progsize = fs.st_size, PROT_READ, MAP_PRIVATE, f, 0);
assert(prog != NULL);
return 0;
}

/* As requested, a little more commentary on this, admittedly bizarre, function.
findmatch receives the current instruction-pointer and a bracket character
for which the "match" is desired. It returns a new instruction-pointer.
*/
int findmatch(int ip, char src){
char q, p="[]";
int i, defer, dir[]= { 1, -1 };
i = strchr(p,src)-p; // at this point, if(src=='[') i=0; else if(src==']') i=1;
ip+=dir[i]; // ie. if(src=='[') ++ip else if(src==']') --ip
// so dir[i] tells us which direction we're going
// next, we reuse the same idiom to check each character as we scan.
// defer counts up or down as we encounter [ and ] and finally reaches 0
// when the match is found.
for (defer=dir[i]; defer!=0; ip+=dir[i]) {
if (ip=progsize) error("mismatch"); // check exceeded bounds
if (q = strchr(p,prog[ip])) { // if the char is a bracket
int j = q-p; // j is 0 or 1
defer+=dir[j]; // adjust the 'defer' level
}
}
return ip - dir[i]; // return new ip value (one past the matched bracket)
}

int run() {
int ip;
for(ip = 0; ip>=0 && ip': ++ptr; break;

My biggest complaint on readability would be your findmatch() function. There are too many non-descriptive variables (i.e. i, j, p, etc). Changing the names to be more descriptive, or adding some comments to elaborate on what you're trying to do would help a lot.

StackExchange Code Review Q#25934, answer score: 8