float_histogram.c

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#include <stdio.h>
#include <math.h>

#define MAX_VALUE 2000.0
#define STEP 0.1

int main(int argc, char *argv[]) {

  char *histogram_filename = argv[1];
  FILE *histogram_file, *infile;
  int num_entries = MAX_VALUE/STEP;
  double *hist;
  float f;
  double data;
  int i;


  hist = (double *)calloc(num_entries, sizeof(double));

  if ((histogram_file = fopen(histogram_filename, "rb")) != NULL) {
    fread(hist, sizeof(double), num_entries, histogram_file);
    fclose(histogram_file);
  }
  infile = stdin;

  while(fscanf(infile, "%f", &f) != EOF) {
    data = (double)f;
    if (data >= MAX_VALUE) {
      fprintf(stderr, "Value %f greater than max. allowed in histogram (%f)\n", data, MAX_VALUE);
      data = 0.9999*MAX_VALUE;
    }
    i = (int)floor(data/STEP);
    hist[i]++;
  }

  histogram_file = fopen(histogram_filename, "wb");
  fwrite(hist, sizeof(double), num_entries, histogram_file);
  fclose(histogram_file);
}