QND tool for comparing two histograms of equal and known bin count.

histdiff.c

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

int main(int argc, char * argv[])
{
	if (argc != 4)
	{
		fprintf(stderr, "usage: histdiff <size> <file1> <file2>\n");
		return -1;
	}
	
	int size = atoi(argv[1]);
	
	FILE * f1, * f2;
	f1 = fopen(argv[2], "r");
	if (! f1)
	{
		perror(argv[2]);
		return -1;
	}
	f2 = fopen(argv[3], "r");
	if (! f2)
	{
		perror(argv[3]);
		return -1;
	}
	
	int differences = 0;
	int totalA = 0;
	int totalB = 0;
	for (int i = 0; i < size; ++ i)
	{
		int binA, binB;
		int countA, countB;
		fscanf(f1, "%d, %d\n", & binA, & countA);
		fscanf(f2, "%d, %d\n", & binB, & countB);
		differences += abs(countA - countB);
		totalA += countA;
		totalB += countB;
	}
	if (totalA != totalB)
		printf("Histogram totals differ! %d %d\n", totalA, totalB);
	printf("%d of %d values in wrong bin.\n", differences, totalA);
	printf("%.6f%% error\n", differences / (double) totalA * 100.0);
	return 0;
}