#include "silleee.h"

silleee silleee_sub(silleee x, silleee y) {
  y ^= 0x80000000;
  return silleee_add(x, y);
}

silleee shift_and_round(int val, int bits) {
  static unsigned masks[24]= {
    0, 1, 3, 7, 0xf, 0x1f, 0x3f, 0x7f, 0xff, 0x1ff, 0x3ff, 0x7ff, 0xfff,
    0x1fff, 0x3fff, 0x7fff, 0xffff, 0x1ffff, 0x3ffff, 0x7ffff, 0xfffff,
    0x1fffff, 0x3fffff, 0x7fffff
  };

  static unsigned masks_ho[24] = {
    0, 1, 2, 4, 8, 0x10, 0x20, 0x40, 0x80, 0x100, 0x200, 0x400, 0x800, 0x1000,
    0x2000, 0x4000, 0x8000, 0x10000, 0x20000, 0x40000, 0x80000, 0x100000,
    0x200000, 0x400000
  };

  int so = val & masks[bits];

  val >>= bits;

  if (so > masks_ho[bits]) val++;
  else if(so == masks_ho[bits]) val += val&1;

  return val;
}

silleee silleee_add(silleee x, silleee y) {
  int dexp;
  long unsigned dmant;
  int dsign;

  int xexp = exponent(x);
  long unsigned xmant = mantissa(x);
  int xsign = sign(x);

  int yexp = exponent(y);
  long unsigned ymant = mantissa(y);
  int ysign = sign(y);

  if (xexp == 127) {
    if (!xmant) {
      if (yexp == 127) {
        if(!ymant) return xsign == ysign ? y : 0x7fc00000;
        else return y;
      }
    } else {
      return x;
    }
  } else if (yexp == 127) {
    return y;
  }

  dexp = yexp;

  if (yexp > xexp) {
    xmant = shift_and_round(xmant, yexp-xexp);
  } else if (yexp < xexp) {
    ymant = shift_and_round(ymant, xexp-yexp);
    dexp = xexp;
  }

  if (ysign ^ xsign) {
    if (xmant > ymant) {
      dmant = xmant - ymant;
      dsign = xmant;
    } else {
      dmant = ymant - xmant;
      dsign = ysign;
    }
  } else {
    dsign = xsign;
    dmant = xmant + ymant;
  }

  if (dmant >= 0x1000000) {
    dmant = shift_and_round(dmant, 1);
    ++dexp;
  } else {
    if (dmant) {
      while ((dmant < 0x800000) && (dexp > -127)) {
        dmant <<= 1;
        --dexp;
      }
    } else {
      dsign = 0;
      dexp = 0;
    }
  }

  return pack_silleee(dsign, dexp, dmant);
}