#include <stdio.h>
#include <stdlib.h>
#include "binread.h"

/* in-place byte swapping */
#define  SWAP(a,b)    (b)^=(a); (a)^=(b); (b)^=(a)
#define  FLIP4(b)     SWAP((b)[0],(b)[3]); SWAP((b)[1],(b)[2])
#define  FLIP8(b)     SWAP((b)[0],(b)[7]); SWAP((b)[1],(b)[6]); \
                      SWAP((b)[2],(b)[5]); SWAP((b)[3],(b)[4])


Vec *binread(const char *bfname, int *n)
{
  FILE *f;
  Vec *v = NULL;
  long startvec, endvec;
  int isflipped = 0;

  if (sizeof(int) != 4) {
    fprintf(stderr, "type 'int' has unexpected size %d\n", (int) sizeof(int));
    return NULL;
  }
  if (bfname == NULL) return NULL;
  if ((f = fopen(bfname,"r")) == NULL) return NULL;
  if (fread(n, sizeof(int), 1, f) != 1) return NULL;
  if ((startvec = ftell(f)) == -1L) return NULL;
  if (fseek(f, 0L, SEEK_END) != 0) return NULL;
  if ((endvec = ftell(f)) == -1L) return NULL;
  if (*n * sizeof(Vec) != endvec - startvec) {
    isflipped = 1;
    FLIP4((unsigned char *)n);
    if (*n * sizeof(Vec) != endvec - startvec) {
      fprintf(stderr, "length of file does not match number of atoms\n");
      return NULL;
    }
  }
  if (fseek(f, 4L, SEEK_SET) != 0) return NULL;
  if ((v = (Vec *) malloc(*n * sizeof(Vec))) == NULL) return NULL;
  if (fread(v, sizeof(Vec), *n, f) != *n) {
    free(v);
    return NULL;
  }
  if (fclose(f) != 0) return v;
  if (isflipped) {
    Vec *p;
    int i;
    for (p = v, i = 0;  i < *n;  i++, p++) {
      FLIP8((unsigned char *)&(p->x));
      FLIP8((unsigned char *)&(p->y));
      FLIP8((unsigned char *)&(p->z));
    }
  }
  return v;
}