simdasciicheck.h

#ifndef SIMDASCIICHECK_H
#define SIMDASCIICHECK_H

#include <emmintrin.h> // SSE2
#include <stdbool.h>   // c99 bool
#include <stddef.h>    // size_t

// The function returns true (1) if all chars passed in src are
// 7-bit values (0x00..0x7F). Otherwise, it returns false (0).
static bool validate_ascii_fast(const char *src, size_t len) {
  size_t i = 0;
  __m128i has_error = _mm_setzero_si128();
  if (len >= 16) {
    for (; i <= len - 16; i += 16) {
      __m128i current_bytes = _mm_loadu_si128((const __m128i *)(src + i));
      has_error = _mm_or_si128(has_error, current_bytes);
    }
  }
  int error_mask = _mm_movemask_epi8(has_error);

  char tail_has_error = 0;
  for (; i < len; i++) {
    tail_has_error |= src[i];
  }
  error_mask |= (tail_has_error & 0x80);

  return !error_mask;
}

#ifdef __AVX2__
#include <x86intrin.h>
// The function returns true (1) if all chars passed in src are
// 7-bit values (0x00..0x7F). Otherwise, it returns false (0).
static bool validate_ascii_fast_avx(const char *src, size_t len) {
  size_t i = 0;
  __m256i has_error = _mm256_setzero_si256();
  if (len >= 32) {
    for (; i <= len - 32; i += 32) {
      __m256i current_bytes = _mm256_loadu_si256((const __m256i *)(src + i));
      has_error = _mm256_or_si256(has_error, current_bytes);
    }
  }
  int error_mask = _mm256_movemask_epi8(has_error);

  char tail_has_error = 0;
  for (; i < len; i++) {
    tail_has_error |= src[i];
  }
  error_mask |= (tail_has_error & 0x80);

  return !error_mask;
}
#endif

#endif