Inspired by ghc naive C-implementation of wc

ascii_wc_like_ghc.c

#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>

static struct { size_t chars, words, lines; } result;

static _Bool process_chunk(const unsigned char *text, const size_t bytes,
                           _Bool prev) {
  result.chars += bytes;
  for (size_t i = 0; i < bytes;) {
    if (text[i] > ' ') {
      // под-цикл по словам
      result.words += !prev;
      prev = 1;
      while (++i < bytes && text[i] > ' ')
        ;
    } else {
      // под-цикл по пробелам
      prev = 0;
      do {
        _Bool non_space = text[i] != ' ' && text[i] - 9 > 4;
        result.words += !prev && non_space;
        result.lines += text[i] == '\n';
        prev = non_space;
      }
      while (++i < bytes && text[i] <= ' ');
    }
  }
  return prev;
}

static int process_fd(int fd) {
  off_t length = lseek(fd, 0, SEEK_END);
  if (length >= 0 && length <= INTPTR_MAX) {
    void *ptr = mmap(NULL, (size_t)length, PROT_READ, MAP_PRIVATE, fd, 0);
    if (ptr == MAP_FAILED) {
      perror("mmap");
      return EXIT_FAILURE;
    }
    process_chunk((const unsigned char *)ptr, (size_t)length, 0);
    munmap(ptr, length);
    return EXIT_SUCCESS;
  }

  if (length < 0 && errno != ESPIPE) {
    perror("leeek");
    return EXIT_FAILURE;
  }

  _Bool state = 0;
  ssize_t chunk;
  for (;;) {
    unsigned char buf[65536];
    chunk = read(fd, buf, sizeof(buf));
    if (chunk < 1)
      break;
    if (chunk < (int)sizeof(buf))
      memset(buf + chunk, ' ', (8 - chunk) & 7);
    state = process_chunk(buf, chunk, state);
  }

  if (chunk < 0) {
    perror("read");
    return EXIT_FAILURE;
  }
  return EXIT_SUCCESS;
}

int main(int argc, const char *argv[]) {
  int rc = 42;
  if (argc > 1) {
    for (int i = 1; i < argc; ++i) {
      int fd =
          (strcmp(argv[i], "-") == 0) ? STDIN_FILENO : open(argv[1], O_RDONLY);
      if (fd < 0) {
        perror("open");
        return EXIT_FAILURE;
      }
      rc = process_fd(fd);
      close(fd);
      if (rc != EXIT_SUCCESS)
        break;
    }
  } else
    rc = process_fd(STDIN_FILENO);

  struct timespec ts = {0, 0};
  if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts))
    perror("clock_gettime(CLOCK_PROCESS_CPUTIME_ID)");

  if (rc == EXIT_SUCCESS)
    printf("lines %zu, words %zu, chars %zu\ntook %.6f seconds\n", result.lines,
           result.words, result.chars, ts.tv_nsec * 1e-9 + ts.tv_sec);
  return rc;
}