inline float manhattan_distance()

in src/annoylib.h [236:259]

• 22 lines of code
• 4 McCabe index (conditional complexity)

inline float manhattan_distance<float>(const float* x, const float* y, int f) {
  float result = 0;
  int i = f;
  if (f > 7) {
    __m256 manhattan = _mm256_setzero_ps();
    __m256 minus_zero = _mm256_set1_ps(-0.0f);
    for (; i > 7; i -= 8) {
      const __m256 x_minus_y = _mm256_sub_ps(_mm256_loadu_ps(x), _mm256_loadu_ps(y));
      const __m256 distance = _mm256_andnot_ps(minus_zero, x_minus_y); // Absolute value of x_minus_y (forces sign bit to zero)
      manhattan = _mm256_add_ps(manhattan, distance);
      x += 8;
      y += 8;
    }
    // Sum all floats in manhattan register.
    result = hsum256_ps_avx(manhattan);
  }
  // Don't forget the remaining values.
  for (; i > 0; i--) {
    result += fabsf(*x - *y);
    x++;
    y++;
  }
  return result;
}