ifが遅いなんて誰が言ったのだろう？

count.c

#include <stdio.h>
#include <stdlib.h>
#define LIST_MAX_LINE 10000
#define MAX_LEN 256

int same_char(const char *s, const char *t);

int main(void)
{
	char *list = (char *)malloc(LIST_MAX_LINE * MAX_LEN);
	int line = LIST_MAX_LINE;
	for (int i = 0; i < LIST_MAX_LINE; i++) {
		char *result = fgets(list + (i * MAX_LEN), MAX_LEN, stdin);
		if (result == NULL) {
			line = i + 1;
			break;
		}
	}
	int total_count = 0;
	for (int i = 0; i < line; i++) {
		for (int j = i; j < line; j++) {
			total_count += same_char(list + (i * MAX_LEN),
						 list + (j * MAX_LEN));
		}
	}
	printf("line: %d, total count: %d\n", line, total_count);
	free(list);
	return 0;
}

count_bench.rb

# frozen_string_literal: true

require 'benchmark'

def make_test(io)
  len = 80
  line_len = 10000
  list = ('a'..'z').to_a
  size = list.size

  line_len.times do
    str = +''
    len.times { str << list[rand(size)] }
    io.puts str
  end
end

list = %w[
  count_eq
  count_if
  count_if_after
  count_if_null
  count_r_eq
  count_r_if
  count_r_if_after
  count_r_if_null
]

main_prog = 'count'
system("gcc -O2 -Wall -std=c11 -c #{main_prog}.c -o #{main_prog}.o")
list.each do |name|
  system("gcc -O2 -Wall -std=c11 -c #{name}.c -o #{name}.o")
  system("gcc -o #{name} #{main_prog}.o #{name}.o")
end

test_text = 'test.txt'
open(test_text, 'w') do |io|
  make_test(io)
end

result = nil
Benchmark.bm(16) do |x|
  list.each do |name|
    current = nil
    x.report(name) do
      current = `#{name} < #{test_text}`
    end
    if result
      if result != current
        raise "not same result... maybe the program have a bug: #{name}.c"
      end
    else
      result = current
    end
  end
end
puts "result -> #{result}"

count_eq.c

int same_char(const char *s, const char *t)
{
	int count = 0;
	while (*s && *t) {
		count += (*s++ == *t++);
	}
	return count;
}

count_if.c

int same_char(const char *s, const char *t)
{
	int count = 0;
	while (*s && *t) {
		if (*s++ == *t++) count++;
	}
	return count;
}

count_if_after.c

int same_char(const char *s, const char *t)
{
	int count = 0;
	while (*s && *t) {
		if (*s == *t) count++;
		s++;
		t++;
	}
	return count;
}

count_if_null.c

int same_char(const char *s, const char *t)
{
	int count = 0;
	while (*s != '\0' && *t != '\0') {
		if (*s == *t) count++;
		s++;
		t++;
	}
	return count;
}

count_r_eq.c

int same_char(const char *restrict s, const char *restrict t)
{
	int count = 0;
	while (*s && *t) {
		count += (*s++ == *t++);
	}
	return count;
}

count_r_if.c

int same_char(const char *restrict s, const char *restrict t)
{
	int count = 0;
	while (*s && *t) {
		if (*s++ == *t++) count++;
	}
	return count;
}

count_r_if_after.c

int same_char(const char *restrict s, const char *restrict t)
{
	int count = 0;
	while (*s && *t) {
		if (*s == *t) count++;
		s++;
		t++;
	}
	return count;
}

count_r_if_null.c

int same_char(const char *restrict s, const char *restrict t)
{
	int count = 0;
	while (*s != '\0' && *t != '\0') {
		if (*s == *t) count++;
		s++;
		t++;
	}
	return count;
}