Naive version of wc which is 5x faster than the real wc. (Doesn't handle locales, utf-8, etc., just counts ASCII words).

wc_naive.c

// Something I whipped up in half an hour.
// Depends on strcspn being super fast.

#define __USE_LARGEFILE64
#define _LARGEFILE_SOURCE
#define _LARGEFILE64_SOURCE

#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>

#define PAGE_SIZE 4096
#define READ_SIZE (16384*4)

#define likely(x)       __builtin_expect((x),1)
#define unlikely(x)     __builtin_expect((x),0)

// TODO find the actual list.
char *WORD_SEPARATORS = "\n\r\t ";

#define min(a,b) \
   ({ __typeof__ (a) _a = (a); \
       __typeof__ (b) _b = (b); \
     _a < _b ? _a : _b; })

int64_t fsize(int fd) { 
  struct stat64 stat;
  fstat64(fd, &stat);
  return stat.st_size;
}

#define IN_TOKEN 0
#define IN_SEPARATOR 1

int wc_helper(char *buf, int64_t *ret, int st) {
  while (*buf != 0) {
    if (likely(st == IN_TOKEN)) {
      // advance until we reach the end of a word, incrementing ret
      // (strcspn apparently uses sse intrinsics these days)
      size_t x = strcspn(buf, WORD_SEPARATORS);
      buf += x;
      if (*buf) {
        (*ret)++;
        st = IN_SEPARATOR;
      }
    } else {
      // advance until we hit another word.
      buf += strspn(buf, WORD_SEPARATORS);
      if (*buf) {
        st = IN_TOKEN;
      }
    }
  }
  return st;
}

int64_t wc(char *fname) {
  int fd = open(fname, O_RDONLY);
  int64_t len = fsize(fd);

  char buf[READ_SIZE+1];

  int64_t left = len;
  int64_t ret = 0;

  int st = 0; // whether or not we are in a separator or a token.

  while (1) {
    ssize_t count = min(left, READ_SIZE);
    ssize_t r = read(fd, buf, count);
    if (r < 0) {
      perror("panic");
      return -1;
    }

    if (r == 0) {
      return ret;
    }

    left -= r;

    // add a null terminator so that "str" operations terminate properly
    buf[r] = '\0';

    st = wc_helper(buf, &ret, st);
  }

  return ret;
}

int main(int argc, char **argv) {
  if (argc < 2) {
    fprintf(stderr, "Must have at least one argument!");
    exit(1);
  }

  char *fname = argv[1];

  int64_t res = wc(fname);
  if (res < 0) {
    return res;
  }
  printf("%ld\n", res);
}