I got inspired by that branchless rust post a couple days ago. Tried it out here and got a ~50% speedup on a 10 million word file. (Averaged over 100 runs). Fi

I got inspired by that branchless rust post a couple days ago. Tried it out here and got a ~50% speedup on a 10 million word file. (Averaged over 100 runs). File IO was the real bottleneck, so I loaded the entire file into RAM and removed the repeated fgetc's so the actual algorithms could be compared. davidkooi@Davids-MacBook-Pro word_count % ./wc_original lorem_ipsum.txt word_counter elapsed time: 0.106370000 seconds The number of words is: 10000000 The number of rows is: 221000 davidkooi@Davids-MacBook-Pro word_count % ./wc_branchless lorem_ipsum.txt word_counter elapsed time: 0.043484000 seconds The number of words is: 10000000 The number of rows is: 221000 How does this work? You're essentially running an edge detector over words so you can for the main loop you can do a psudo-filter over a 2-sample sliding window. This works because isalnum returns an int which is 0 when it's not a alphanumeric character. So logically the input stream becomes _ _ _---_ _ _---_ _ -- where ___ is 0 and --- is > 0. You can detect an edge by having a 2-sample "kernel" [1, 0] which you add with a 2-sample sliding window. That gives us these cases: - no-word section the result is [1, 0] + [0, 0] = [1, 0]. - a rising edge section the result is [1, 0] + [0, >0] = [1, >0] - a word section the result is [1, 0] + [>0, >0] = [>0, >0] - a falling edge section the result is [1, 0] + [>0, 0] = [>0, 0] So we can use the rising edge case to increment the word count. Row count can be incremented without a conditional as well. Resultant loop is: uint32_t i; unsigned char new_ch; int prev_now[2] = {0, 0}; int PREV_IDX = 0; int NOW_IDX = 1; int kernel[2] = {1, 0}; int result[2] = {0, 0}; for (i = 0; i < file_size_bytes; i++){ // Update now new_ch = data[i]; prev_now[NOW_IDX] = isalnum((unsigned char)new_ch); // Edge detect result[0] = prev_now[NOW_IDX] + kernel[0]; result[1] = prev_now[PREV_IDX] + kernel[1]; *w_cnt += result[0] == 1 && result[1] > 0; *r_cnt += new_ch == '\n'; // Shift without a move operation PREV_IDX = 1 - PREV_IDX; NOW_IDX = 1 - NOW_IDX; // Shift with a move operation //prev_now[PREV_IDX] = prev_now[NOW_IDX]; }