// hash mining in multiple threads
//
#include <stdio.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>

void error( const char *msg) { perror(msg); exit(1); }

#define offset_basis 2166136261U
#define FNV_prime 16777619U

// FNV hash from http://www.isthe.com/chongo/tech/comp/fnv/
//
unsigned int fnv1a( unsigned char *d, size_t n) {
  unsigned int hash = offset_basis;
  while( n--) { hash ^= *d++; hash *= FNV_prime; }
  return hash & 0xFFFFFF; // bottom 24 bits
}


unsigned int ans = 0xabcdef; // desired hash output

typedef struct { // per-thread data
  int tn;
  unsigned int start, stop;
} Data;

#define NT 1 // number of threads

Data d[NT];
  
void *f(void *p) { // thread worker
  Data *d = p;
  printf( "f %i %u %u\n", d->tn, d->start, d->stop);
  // *** unsigned overflow bug here if stop=UINT_MAX
  for( unsigned int x = d->start; x <= d->stop; ++x) {
    char buf[BUFSIZ]; sprintf( buf, "%08x", x);
    // unsigned int h = fnv1a( (unsigned char *) &x, sizeof(x) );
    // if( h == ans) { printf( "f x %08x ans %x\n", x, h); break; }
    unsigned int h = fnv1a( (unsigned char *) buf, 8 );
    if( h == ans) { printf( "f x %s ans %x\n", buf, h); break; }
  }
  return 0;
}

int main( void) {
  setbuf( stdout, 0);
  int fd[2]; if( pipe(fd) < 0) perror("pipe");
  dup2(fd[0],0); // connect stdin to pipe
  dup2(fd[1],1); // connect stdout to pipe
  close(fd[0]); close(fd[1]); // close unneeded descriptors

  // *** unsigned overflow bug here if NT=1
  unsigned int start = 0, count = (UINT_MAX+1ULL)/NT;
  for( int i = 0; i < NT; ++i) {
    d[i].tn = i;
    d[i].start = start;
    d[i].stop = (i == NT-1) ? UINT_MAX : start + (count - 1);
    start += count;
  }

  pthread_t t[NT];
  for( int i = 0; i < NT; ++i)
    if( pthread_create( &t[i], 0, f, &d[i]) != 0)
       error( "pthread_create");

  char msg[BUFSIZ];
  while( fgets(msg,BUFSIZ,stdin)) { // read from the pipe
    fprintf( stderr, "main got: %s", msg); // write to terminal
    if( strstr( msg, "ans") ) break; // *** stuck in loop here if ans never found
  }
}