Function decimal_round

strings/decimal.c:1561–1766

*/

int
decimal_round(const decimal_t *from, decimal_t *to, int scale,
              decimal_round_mode mode)
{
  int frac0=scale>0 ? ROUND_UP(scale) : (scale + 1)/DIG_PER_DEC1,
    frac1=ROUND_UP(from->frac), UNINIT_VAR(round_digit),
    intg0=ROUND_UP(from->intg), error=E_DEC_OK, len=to->len;

  dec1 *buf0=from->buf, *buf1=to->buf, x, y, carry=0;
  int first_dig;

  sanity(to);

  switch (mode) {
  case HALF_UP:
  case HALF_EVEN:       round_digit=5; break;
  case CEILING:         round_digit= from->sign ? 10 : 0; break;
  case FLOOR:           round_digit= from->sign ? 0 : 10; break;
  case TRUNCATE:        round_digit=10; break;
  default: DBUG_ASSERT(0);
  }

  /*
    For my_decimal we always use len == DECIMAL_BUFF_LENGTH == 9
    For internal testing here (ifdef MAIN) we always use len == 100/4
   */
  DBUG_ASSERT(from->len == to->len);

  if (unlikely(frac0+intg0 > len))
  {
    frac0=len-intg0;
    scale=frac0*DIG_PER_DEC1;
    error=E_DEC_TRUNCATED;
  }

  if (scale+from->intg < 0)
  {
    decimal_make_zero(to);
    return E_DEC_OK;
  }

  if (to != from)
  {
    dec1 *p0= buf0 + intg0 + MY_MAX(frac1, frac0);
    dec1 *p1= buf1 + intg0 + MY_MAX(frac1, frac0);

    DBUG_ASSERT(p0 - buf0 <= len);
    DBUG_ASSERT(p1 - buf1 <= len);

    while (buf0 < p0)
      *(--p1) = *(--p0);

    buf0=to->buf;
    buf1=to->buf;
    to->sign=from->sign;
    to->intg= MY_MIN(intg0, len) * DIG_PER_DEC1;
  }