inline float manhattan_distance()

in src/annoylib.h [312:333]

• 20 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 > 15) {
    __m512 manhattan = _mm512_setzero_ps();
    for (; i > 15; i -= 16) {
      const __m512 x_minus_y = _mm512_sub_ps(_mm512_loadu_ps(x), _mm512_loadu_ps(y));
      manhattan = _mm512_add_ps(manhattan, _mm512_abs_ps(x_minus_y));
      x += 16;
      y += 16;
    }
    // Sum all floats in manhattan register.
    result = _mm512_reduce_add_ps(manhattan);
  }
  // Don't forget the remaining values.
  for (; i > 0; i--) {
    result += fabsf(*x - *y);
    x++;
    y++;
  }
  return result;
}