GC count in c but allocating the correc file size

gc_ds_wholefile_tbl_parallel_size.c

#include <stdio.h>
#include <stdlib.h>
#define MAXFLEN 2600000000 /* Larger than the file. */
#include <sys/stat.h>

int main()
{
  char tablegc[256];
  char tableat[256];
  int gc=0;
  int at=0;
  char fn[] =  "Homo_sapeins.GR37.dba_rm.chromsome.Y.fa";
  FILE *f=fopen(fn,"r");
  struct stat st;
  int len=MAXFLEN;
  if (stat(fn, &st) == 0)
           len = st.st_size;
  char *m=malloc(len);
  int items=fread(m,1,len,f); /* Read the whole file into memory. */
  char *ptr=m;
  int nums, i;
  while (*ptr++!='\n'); /* Find end of first line. */
  for (i=0; i<256; i++)
    tablegc[i]=0;
  for (i=0; i<256; i++)
    tableat[i]=0;
  tableat['A']=1;
  tableat['T']=1;
  tablegc['C']=1;
  tablegc['G']=1;
  nums=items-(ptr-m);
#pragma omp parallel for private(i),reduction(+:gc),reduction(+:at)
  for (i=0; i<nums; i++) {
    char c=ptr[i];
    at+=tableat[(int)c];
    gc+=tablegc[(int)c];
  }
  fclose(f);
  free(m);
  int total = at + gc;
  printf("%.10f\n",(100.*gc)/total);
  return 0;
}