xref: /dragonfly/contrib/mpfr/src/add1sp.c (revision ab6d115f)

/* mpfr_add1sp -- internal function to perform a "real" addition
   All the op must have the same precision

Copyright 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
Contributed by the AriC and Caramel projects, INRIA.

This file is part of the GNU MPFR Library.

The GNU MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.

The GNU MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */

#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"

/* Check if we have to check the result of mpfr_add1sp with mpfr_add1 */
#ifdef WANT_ASSERT
# if WANT_ASSERT >= 2

int mpfr_add1sp2 (mpfr_ptr, mpfr_srcptr, mpfr_srcptr, mpfr_rnd_t);
int mpfr_add1sp (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode)
{
  mpfr_t tmpa, tmpb, tmpc;
  int inexb, inexc, inexact, inexact2;

  mpfr_init2 (tmpa, MPFR_PREC (a));
  mpfr_init2 (tmpb, MPFR_PREC (b));
  mpfr_init2 (tmpc, MPFR_PREC (c));

  inexb = mpfr_set (tmpb, b, MPFR_RNDN);
  MPFR_ASSERTN (inexb == 0);

  inexc = mpfr_set (tmpc, c, MPFR_RNDN);
  MPFR_ASSERTN (inexc == 0);

  inexact2 = mpfr_add1 (tmpa, tmpb, tmpc, rnd_mode);
  inexact  = mpfr_add1sp2 (a, b, c, rnd_mode);

  if (mpfr_cmp (tmpa, a) || inexact != inexact2)
    {
      fprintf (stderr, "add1 & add1sp return different values for %s\n"
               "Prec_a = %lu, Prec_b = %lu, Prec_c = %lu\nB = ",
               mpfr_print_rnd_mode (rnd_mode),
               (unsigned long) MPFR_PREC (a),
               (unsigned long) MPFR_PREC (b),
               (unsigned long) MPFR_PREC (c));
      mpfr_fprint_binary (stderr, tmpb);
      fprintf (stderr, "\nC = ");
      mpfr_fprint_binary (stderr, tmpc);
      fprintf (stderr, "\n\nadd1  : ");
      mpfr_fprint_binary (stderr, tmpa);
      fprintf (stderr, "\nadd1sp: ");
      mpfr_fprint_binary (stderr, a);
      fprintf (stderr, "\nInexact sp = %d | Inexact = %d\n",
               inexact, inexact2);
      MPFR_ASSERTN (0);
    }
  mpfr_clears (tmpa, tmpb, tmpc, (mpfr_ptr) 0);
  return inexact;
}
#  define mpfr_add1sp mpfr_add1sp2
# endif
#endif

/* Debugging support */
#ifdef DEBUG
# undef DEBUG
# define DEBUG(x) (x)
#else
# define DEBUG(x) /**/
#endif

/* compute sign(b) * (|b| + |c|)
   Returns 0 iff result is exact,
   a negative value when the result is less than the exact value,
   a positive value otherwise. */
int
mpfr_add1sp (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode)
{
  mpfr_uexp_t d;
  mpfr_prec_t p;
  unsigned int sh;
  mp_size_t n;
  mp_limb_t *ap, *cp;
  mpfr_exp_t bx;
  mp_limb_t limb;
  int inexact;
  MPFR_TMP_DECL(marker);

  MPFR_TMP_MARK(marker);

  MPFR_ASSERTD(MPFR_PREC(a) == MPFR_PREC(b) && MPFR_PREC(b) == MPFR_PREC(c));
  MPFR_ASSERTD(MPFR_IS_PURE_FP(b));
  MPFR_ASSERTD(MPFR_IS_PURE_FP(c));
  MPFR_ASSERTD(MPFR_GET_EXP(b) >= MPFR_GET_EXP(c));

  /* Read prec and num of limbs */
  p = MPFR_PREC(b);
  n = MPFR_PREC2LIMBS (p);
  MPFR_UNSIGNED_MINUS_MODULO(sh, p);
  bx = MPFR_GET_EXP(b);
  d = (mpfr_uexp_t) (bx - MPFR_GET_EXP(c));

  DEBUG (printf ("New add1sp with diff=%lu\n", (unsigned long) d));

  if (MPFR_UNLIKELY(d == 0))
    {
      /* d==0 */
      DEBUG( mpfr_print_mant_binary("C= ", MPFR_MANT(c), p) );
      DEBUG( mpfr_print_mant_binary("B= ", MPFR_MANT(b), p) );
      bx++;                                /* exp + 1 */
      ap = MPFR_MANT(a);
      limb = mpn_add_n(ap, MPFR_MANT(b), MPFR_MANT(c), n);
      DEBUG( mpfr_print_mant_binary("A= ", ap, p) );
      MPFR_ASSERTD(limb != 0);             /* There must be a carry */
      limb = ap[0];                        /* Get LSB (In fact, LSW) */
      mpn_rshift(ap, ap, n, 1);            /* Shift mantissa A */
      ap[n-1] |= MPFR_LIMB_HIGHBIT;        /* Set MSB */
      ap[0]   &= ~MPFR_LIMB_MASK(sh);      /* Clear LSB bit */
      if (MPFR_LIKELY((limb&(MPFR_LIMB_ONE<<sh)) == 0)) /* Check exact case */
        { inexact = 0; goto set_exponent; }
      /* Zero: Truncate
         Nearest: Even Rule => truncate or add 1
         Away: Add 1 */
      if (MPFR_LIKELY(rnd_mode==MPFR_RNDN))
        {
          if (MPFR_LIKELY((ap[0]&(MPFR_LIMB_ONE<<sh))==0))
            { inexact = -1; goto set_exponent; }
          else
            goto add_one_ulp;
        }
      MPFR_UPDATE_RND_MODE(rnd_mode, MPFR_IS_NEG(b));
      if (rnd_mode==MPFR_RNDZ)
        { inexact = -1; goto set_exponent; }
      else
        goto add_one_ulp;
    }
  else if (MPFR_UNLIKELY (d >= p))
    {
      if (MPFR_LIKELY (d > p))
        {
          /* d > p : Copy B in A */
          /* Away:    Add 1
             Nearest: Trunc
             Zero:    Trunc */
          if (MPFR_LIKELY (rnd_mode==MPFR_RNDN
                           || MPFR_IS_LIKE_RNDZ (rnd_mode, MPFR_IS_NEG (b))))
            {
            copy_set_exponent:
              ap = MPFR_MANT (a);
              MPN_COPY (ap, MPFR_MANT(b), n);
              inexact = -1;
              goto set_exponent;
            }
          else
            {
            copy_add_one_ulp:
              ap = MPFR_MANT(a);
              MPN_COPY (ap, MPFR_MANT(b), n);
              goto add_one_ulp;
            }
        }
      else
        {
          /* d==p : Copy B in A */
          /* Away:    Add 1
             Nearest: Even Rule if C is a power of 2, else Add 1
             Zero:    Trunc */
          if (MPFR_LIKELY(rnd_mode==MPFR_RNDN))
            {
              /* Check if C was a power of 2 */
              cp = MPFR_MANT(c);
              if (MPFR_UNLIKELY(cp[n-1] == MPFR_LIMB_HIGHBIT))
                {
                  mp_size_t k = n-1;
                  do {
                    k--;
                  } while (k>=0 && cp[k]==0);
                  if (MPFR_UNLIKELY(k<0))
                    /* Power of 2: Even rule */
                    if ((MPFR_MANT (b)[0]&(MPFR_LIMB_ONE<<sh))==0)
                      goto copy_set_exponent;
                }
              /* Not a Power of 2 */
              goto copy_add_one_ulp;
            }
          else if (MPFR_IS_LIKE_RNDZ (rnd_mode, MPFR_IS_NEG (b)))
            goto copy_set_exponent;
          else
            goto copy_add_one_ulp;
        }
    }
  else
    {
      mp_limb_t mask;
      mp_limb_t bcp, bcp1; /* Cp and C'p+1 */

      /* General case: 1 <= d < p */
      cp = MPFR_TMP_LIMBS_ALLOC (n);

      /* Shift c in temporary allocated place */
      {
        mpfr_uexp_t dm;
        mp_size_t m;

        dm = d % GMP_NUMB_BITS;
        m = d / GMP_NUMB_BITS;
        if (MPFR_UNLIKELY(dm == 0))
          {
            /* dm = 0 and m > 0: Just copy */
            MPFR_ASSERTD(m!=0);
            MPN_COPY(cp, MPFR_MANT(c)+m, n-m);
            MPN_ZERO(cp+n-m, m);
          }
        else if (MPFR_LIKELY(m == 0))
          {
            /* dm >=1 and m == 0: just shift */
            MPFR_ASSERTD(dm >= 1);
            mpn_rshift(cp, MPFR_MANT(c), n, dm);
          }
        else
          {
            /* dm > 0 and m > 0: shift and zero  */
            mpn_rshift(cp, MPFR_MANT(c)+m, n-m, dm);
            MPN_ZERO(cp+n-m, m);
          }
      }

      DEBUG( mpfr_print_mant_binary("Before", MPFR_MANT(c), p) );
      DEBUG( mpfr_print_mant_binary("B=    ", MPFR_MANT(b), p) );
      DEBUG( mpfr_print_mant_binary("After ", cp, p) );

      /* Compute bcp=Cp and bcp1=C'p+1 */
      if (MPFR_LIKELY (sh > 0))
        {
          /* Try to compute them from C' rather than C */
          bcp = (cp[0] & (MPFR_LIMB_ONE<<(sh-1))) ;
          if (MPFR_LIKELY(cp[0]&MPFR_LIMB_MASK(sh-1)))
            bcp1 = 1;
          else
            {
              /* We can't compute C'p+1 from C'. Compute it from C */
              /* Start from bit x=p-d+sh in mantissa C
                 (+sh since we have already looked sh bits in C'!) */
              mpfr_prec_t x = p-d+sh-1;
              if (MPFR_LIKELY(x>p))
                /* We are already looked at all the bits of c, so C'p+1 = 0*/
                bcp1 = 0;
              else
                {
                  mp_limb_t *tp = MPFR_MANT(c);
                  mp_size_t kx = n-1 - (x / GMP_NUMB_BITS);
                  mpfr_prec_t sx = GMP_NUMB_BITS-1-(x%GMP_NUMB_BITS);
                  DEBUG (printf ("(First) x=%lu Kx=%ld Sx=%lu\n",
                                 (unsigned long) x, (long) kx,
                                 (unsigned long) sx));
                  /* Looks at the last bits of limb kx (if sx=0 does nothing)*/
                  if (tp[kx] & MPFR_LIMB_MASK(sx))
                    bcp1 = 1;
                  else
                    {
                      /*kx += (sx==0);*/
                      /*If sx==0, tp[kx] hasn't been checked*/
                      do {
                        kx--;
                      } while (kx>=0 && tp[kx]==0);
                      bcp1 = (kx >= 0);
                    }
                }
            }
        }
      else /* sh == 0 */
        {
          /* Compute Cp and C'p+1 from C with sh=0 */
          mp_limb_t *tp = MPFR_MANT(c);
          /* Start from bit x=p-d in mantissa C */
          mpfr_prec_t  x = p-d;
          mp_size_t   kx = n-1 - (x / GMP_NUMB_BITS);
          mpfr_prec_t sx = GMP_NUMB_BITS-1-(x%GMP_NUMB_BITS);
          MPFR_ASSERTD(p >= d);
          bcp = tp[kx] & (MPFR_LIMB_ONE<<sx);
          /* Looks at the last bits of limb kx (If sx=0, does nothing)*/
          if (tp[kx]&MPFR_LIMB_MASK(sx))
            bcp1 = 1;
          else
            {
              do {
                kx--;
              } while (kx>=0 && tp[kx]==0);
              bcp1 = (kx>=0);
            }
        }
      DEBUG (printf("sh=%u Cp=%lu C'p+1=%lu\n", sh,
                    (unsigned long) bcp, (unsigned long) bcp1));

      /* Clean shifted C' */
      mask = ~MPFR_LIMB_MASK(sh);
      cp[0] &= mask;

      /* Add the mantissa c from b in a */
      ap = MPFR_MANT(a);
      limb = mpn_add_n (ap, MPFR_MANT(b), cp, n);
      DEBUG( mpfr_print_mant_binary("Add=  ", ap, p) );

      /* Check for overflow */
      if (MPFR_UNLIKELY (limb))
        {
          limb = ap[0] & (MPFR_LIMB_ONE<<sh); /* Get LSB */
          mpn_rshift (ap, ap, n, 1);          /* Shift mantissa*/
          bx++;                               /* Fix exponent */
          ap[n-1] |= MPFR_LIMB_HIGHBIT;       /* Set MSB */
          ap[0]   &= mask;                    /* Clear LSB bit */
          bcp1    |= bcp;                     /* Recompute C'p+1 */
          bcp      = limb;                    /* Recompute Cp */
          DEBUG (printf ("(Overflow) Cp=%lu C'p+1=%lu\n",
                         (unsigned long) bcp, (unsigned long) bcp1));
          DEBUG (mpfr_print_mant_binary ("Add=  ", ap, p));
        }

      /* Round:
          Zero: Truncate but could be exact.
          Away: Add 1 if Cp or C'p+1 !=0
          Nearest: Truncate but could be exact if Cp==0
                   Add 1 if C'p+1 !=0,
                   Even rule else */
      if (MPFR_LIKELY(rnd_mode == MPFR_RNDN))
        {
          if (MPFR_LIKELY(bcp == 0))
            { inexact = MPFR_LIKELY(bcp1) ? -1 : 0; goto set_exponent; }
          else if (MPFR_UNLIKELY(bcp1==0) && (ap[0]&(MPFR_LIMB_ONE<<sh))==0)
            { inexact = -1; goto set_exponent; }
          else
            goto add_one_ulp;
        }
      MPFR_UPDATE_RND_MODE(rnd_mode, MPFR_IS_NEG(b));
      if (rnd_mode == MPFR_RNDZ)
        {
          inexact = MPFR_LIKELY(bcp || bcp1) ? -1 : 0;
          goto set_exponent;
        }
      else
        {
          if (MPFR_UNLIKELY(bcp==0 && bcp1==0))
            { inexact = 0; goto set_exponent; }
          else
            goto add_one_ulp;
        }
    }
  MPFR_ASSERTN(0);

 add_one_ulp:
  /* add one unit in last place to a */
  DEBUG( printf("AddOneUlp\n") );
  if (MPFR_UNLIKELY( mpn_add_1(ap, ap, n, MPFR_LIMB_ONE<<sh) ))
    {
      /* Case 100000x0 = 0x1111x1 + 1*/
      DEBUG( printf("Pow of 2\n") );
      bx++;
      ap[n-1] = MPFR_LIMB_HIGHBIT;
    }
  inexact = 1;

 set_exponent:
  if (MPFR_UNLIKELY(bx > __gmpfr_emax)) /* Check for overflow */
    {
      DEBUG( printf("Overflow\n") );
      MPFR_TMP_FREE(marker);
      MPFR_SET_SAME_SIGN(a,b);
      return mpfr_overflow(a, rnd_mode, MPFR_SIGN(a));
    }
  MPFR_SET_EXP (a, bx);
  MPFR_SET_SAME_SIGN(a,b);

  MPFR_TMP_FREE(marker);
  MPFR_RET (inexact * MPFR_INT_SIGN (a));
}