Simple AVX2-enabled version of ASCII-only wc util

ascii_wc_avx2.c

/*
 * zlib License, see https://en.wikipedia.org/wiki/Zlib_License
 *
 * Copyright (c) 2020 Leonid Yuriev <leo@yuriev.ru>,
 * Simple portable optimized ASCII-only version of wc tool.
 * Just for fun &
 * https://en.wikipedia.org/wiki/The_Computer_Language_Benchmarks_Game
 *
 * This software is provided 'as-is', without any express or implied
 * warranty. In no event will the authors be held liable for any damages
 * arising from the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software. If you use this software
 *    in a product, an acknowledgement in the product documentation would be
 *    appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 *
 */
#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>

#include <x86intrin.h>

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

static unsigned process_chunk(const unsigned char *text, const size_t bytes,
                              _Bool was_space) {
  result.chars += bytes;
  /* This loop was copied from the https://habr.com/ru/post/489898/ article
   * with minor changes */
  for (size_t i = 0; i < bytes; i += 32) {
    _mm_prefetch(text + i + 32 * 64, _MM_HINT_NTA);

    __m256i const c = _mm256_load_si256((__m256i *)(text + i));
    uint32_t is_newline_mask =
        _mm256_movemask_epi8(_mm256_cmpeq_epi8(c, _mm256_set1_epi8('\n')));

    uint32_t is_space_mask = _mm256_movemask_epi8(
        _mm256_andnot_si256(c, _mm256_sub_epi8(c, _mm256_set1_epi8(' ' + 1))));
    uint32_t was_space_mask = (was_space ? 1 : 0) | (is_space_mask << 1);

    result.lines += _mm_popcnt_u32(is_newline_mask);
    result.words += _mm_popcnt_u32(is_space_mask & ~was_space_mask);
    was_space = is_space_mask & 0x80000000;
  }

  return was_space;
}

/******************************************************************************/

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, ' ', (32 - chunk) & 31);
    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;
}