コード例 #1
0
ファイル: invert.c プロジェクト: AaronNGray/texlive-libs
void
mpn_invert (mp_ptr ip, mp_srcptr dp, mp_size_t n, mp_ptr scratch)
{
  ASSERT (n > 0);
  ASSERT (dp[n-1] & GMP_NUMB_HIGHBIT);
  ASSERT (! MPN_OVERLAP_P (ip, n, dp, n));
  ASSERT (! MPN_OVERLAP_P (ip, n, scratch, mpn_invertappr_itch(n)));
  ASSERT (! MPN_OVERLAP_P (dp, n, scratch, mpn_invertappr_itch(n)));

  if (n == 1)
    invert_limb (*ip, *dp);
  else if (BELOW_THRESHOLD (n, INV_APPR_THRESHOLD))
    {
	/* Maximum scratch needed by this branch: 2*n */
	mp_size_t i;
	mp_ptr xp;

	xp = scratch;				/* 2 * n limbs */
	/* n > 1 here */
	i = n;
	do
	  xp[--i] = GMP_NUMB_MAX;
	while (i);
	mpn_com (xp + n, dp, n);
	if (n == 2) {
	  mpn_divrem_2 (ip, 0, xp, 4, dp);
	} else {
	  gmp_pi1_t inv;
	  invert_pi1 (inv, dp[n-1], dp[n-2]);
	  /* FIXME: should we use dcpi1_div_q, for big sizes? */
	  mpn_sbpi1_div_q (ip, xp, 2 * n, dp, n, inv.inv32);
	}
    }
  else { /* Use approximated inverse; correct the result if needed. */
      mp_limb_t e; /* The possible error in the approximate inverse */

      ASSERT ( mpn_invert_itch (n) >= mpn_invertappr_itch (n) );
      e = mpn_ni_invertappr (ip, dp, n, scratch);

      if (UNLIKELY (e)) { /* Assume the error can only be "0" (no error) or "1". */
	/* Code to detect and correct the "off by one" approximation. */
	mpn_mul_n (scratch, ip, dp, n);
	e = mpn_add_n (scratch, scratch, dp, n); /* FIXME: we only need e.*/
	if (LIKELY(e)) /* The high part can not give a carry by itself. */
	  e = mpn_add_nc (scratch + n, scratch + n, dp, n, e); /* FIXME:e */
	/* If the value was wrong (no carry), correct it (increment). */
	e ^= CNST_LIMB (1);
	MPN_INCR_U (ip, n, e);
      }
  }
}
コード例 #2
0
ファイル: invert.c プロジェクト: AlexeiSheplyakov/gmp.pkg
void
mpn_invert (mp_ptr ip, mp_srcptr dp, mp_size_t n, mp_ptr scratch)
{
  ASSERT (n > 0);
  ASSERT (dp[n-1] & GMP_NUMB_HIGHBIT);
  ASSERT (! MPN_OVERLAP_P (ip, n, dp, n));
  ASSERT (! MPN_OVERLAP_P (ip, n, scratch, mpn_invertappr_itch(n)));
  ASSERT (! MPN_OVERLAP_P (dp, n, scratch, mpn_invertappr_itch(n)));

  if (n == 1)
    invert_limb (*ip, *dp);
  else {
    TMP_DECL;

    TMP_MARK;
    if (BELOW_THRESHOLD (n, INV_APPR_THRESHOLD))
      {
	/* Maximum scratch needed by this branch: 2*n */
	mp_size_t i;
	mp_ptr xp;

	xp = scratch;				/* 2 * n limbs */
	for (i = n - 1; i >= 0; i--)
	  xp[i] = GMP_NUMB_MAX;
	mpn_com (xp + n, dp, n);
	if (n == 2) {
	  mpn_divrem_2 (ip, 0, xp, 4, dp);
	} else {
	  gmp_pi1_t inv;
	  invert_pi1 (inv, dp[n-1], dp[n-2]);
	  /* FIXME: should we use dcpi1_div_q, for big sizes? */
	  mpn_sbpi1_div_q (ip, xp, 2 * n, dp, n, inv.inv32);
	}
      }
    else { /* Use approximated inverse; correct the result if needed. */
      mp_limb_t e; /* The possible error in the approximate inverse */

      ASSERT ( mpn_invert_itch (n) >= mpn_invertappr_itch (n) );
      e = mpn_ni_invertappr (ip, dp, n, scratch);

      if (UNLIKELY (e)) { /* Assume the error can only be "0" (no error) or "1". */
	/* Code to detect and correct the "off by one" approximation. */
	mpn_mul_n (scratch, ip, dp, n);
	ASSERT_NOCARRY (mpn_add_n (scratch + n, scratch + n, dp, n));
	if (! mpn_add (scratch, scratch, 2*n, dp, n))
	  MPN_INCR_U (ip, n, 1); /* The value was wrong, correct it.  */
      }
    }
    TMP_FREE;
  }
}