inline float16 cpu_float2half_rn()

in gloo/types.h [251:310]

• 47 lines of code
• 9 McCabe index (conditional complexity)

inline float16 cpu_float2half_rn(float f) {
  float16 ret;

  static_assert(
      sizeof(unsigned int) == sizeof(float),
      "Programming error sizeof(unsigned int) != sizeof(float)");

  unsigned* xp = reinterpret_cast<unsigned int*>(&f);
  unsigned x = *xp;
  unsigned u = (x & 0x7fffffff), remainder, shift, lsb, lsb_s1, lsb_m1;
  unsigned sign, exponent, mantissa;

  // Get rid of +NaN/-NaN case first.
  if (u > 0x7f800000) {
    ret.x = 0x7fffU;
    return ret;
  }

  sign = ((x >> 16) & 0x8000);

  // Get rid of +Inf/-Inf, +0/-0.
  if (u > 0x477fefff) {
    ret.x = sign | 0x7c00U;
    return ret;
  }
  if (u < 0x33000001) {
    ret.x = (sign | 0x0000);
    return ret;
  }

  exponent = ((u >> 23) & 0xff);
  mantissa = (u & 0x7fffff);

  if (exponent > 0x70) {
    shift = 13;
    exponent -= 0x70;
  } else {
    shift = 0x7e - exponent;
    exponent = 0;
    mantissa |= 0x800000;
  }
  lsb = (1 << shift);
  lsb_s1 = (lsb >> 1);
  lsb_m1 = (lsb - 1);

  // Round to nearest even.
  remainder = (mantissa & lsb_m1);
  mantissa >>= shift;
  if (remainder > lsb_s1 || (remainder == lsb_s1 && (mantissa & 0x1))) {
    ++mantissa;
    if (!(mantissa & 0x3ff)) {
      ++exponent;
      mantissa = 0;
    }
  }

  ret.x = (sign | (exponent << 10) | mantissa);

  return ret;
}