niceSOFT/mpfr | Gitverse

src/cache.c
196 строк6 KB
Vincent Lefèvre
08 янв 2020, 21:11
08 янв 2020, 21:11d4296f9
/* mpfr_cache -- cache interface for multiple-precision constants in MPFR.

Copyright 2004-2020 Free Software Foundation, Inc.
Contributed by the AriC and Caramba 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
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */

#include "mpfr-impl.h"

#if 0 /* this function is not used/documented/tested so far, it could be
         useful if some user wants to add a new constant to mpfr, and
         implement a cache mechanism for that constant */
void
mpfr_init_cache (mpfr_cache_t cache, int (*func)(mpfr_ptr, mpfr_rnd_t))
{
  MPFR_PREC (cache->x) = 0; /* Invalid prec to detect that the cache is not
                               valid. Maybe add a flag? */
  cache->func = func;
}
#endif

void
mpfr_clear_cache (mpfr_cache_t cache)
{
  if (MPFR_UNLIKELY (MPFR_PREC (cache->x) != 0))
    {
      /* Get the cache in read-write mode */
      MPFR_LOCK_WRITE(cache->lock);

      if (MPFR_LIKELY (MPFR_PREC (cache->x) != 0))
        {
          mpfr_clear (cache->x);
          MPFR_PREC (cache->x) = 0;
        }

      /* Free the cache in read-write mode */
      MPFR_UNLOCK_WRITE(cache->lock);
    }
}

int
mpfr_cache (mpfr_ptr dest, mpfr_cache_t cache, mpfr_rnd_t rnd)
{
  mpfr_prec_t dprec = MPFR_PREC (dest);
  mpfr_prec_t cprec;  /* precision of the cache */
  int inexact, sign;
  MPFR_SAVE_EXPO_DECL (expo);

  /* Call the initialisation function of the cache if it's needed */
  MPFR_DEFERRED_INIT_CALL(cache);

  MPFR_SAVE_EXPO_MARK (expo);

  /* Get the cache in read-only mode */
  MPFR_LOCK_READ(cache->lock);
  /* Read the precision within the cache */
  cprec = MPFR_PREC (cache->x);
  if (MPFR_UNLIKELY (dprec > cprec))
    {
      /* Free the cache in read-only mode */
      /* And get the cache in read-write mode */
      MPFR_LOCK_READ2WRITE(cache->lock);

      /* Retest the precision once we get the lock (since it might have
         changed). If there is no lock, there is no harm in this code. */
      cprec = MPFR_PREC (cache->x);
      if (MPFR_LIKELY (dprec > cprec))
        {
          /* No previous result in the cache or the precision of the
             previous result is not sufficient. */
          if (MPFR_UNLIKELY (cprec == 0))  /* No previous result. */
            {
              cprec = dprec;
              mpfr_init2 (cache->x, cprec);
            }
          else
            {
              /* We increase the cache size by at least 10% to avoid
                 invalidating the cache many times if one performs
                 several computations with small increase of precision. */
              cprec += cprec / 10;
              if (cprec < dprec)
                cprec = dprec;
              /* no need to keep the previous value */
              mpfr_set_prec (cache->x, cprec);
            }

          cache->inexact = (*cache->func) (cache->x, MPFR_RNDN);
        }

      /* Free the cache in read-write mode */
      /* Get the cache in read-only mode */
      MPFR_LOCK_WRITE2READ(cache->lock);
    }

  /* now cprec >= dprec is the precision of cache->x */
  MPFR_ASSERTD (cprec >= dprec);
  MPFR_ASSERTD (MPFR_PREC (cache->x) == cprec);

  /* First, check if the cache has the exact value (unlikely).
     Else the exact value is between (assuming x=cache->x > 0):
       x and x+ulp(x) if cache->inexact < 0,
       x-ulp(x) and x if cache->inexact > 0,
     and abs(x-exact) <= ulp(x)/2. */

  /* we assume all cached constants are positive */
  MPFR_ASSERTN (MPFR_IS_POS (cache->x)); /* TODO... */
  sign = MPFR_SIGN (cache->x);
  MPFR_EXP (dest) = MPFR_GET_EXP (cache->x);
  MPFR_SET_SIGN (dest, sign);

  /* round cache->x from precision cprec down to precision dprec;
     since we are in extended exponent range, for the values considered
     here, an overflow is not possible (and wouldn't make much sense). */
  MPFR_RNDRAW_GEN (inexact, dest,
                   MPFR_MANT (cache->x), cprec, rnd, sign,
                   if (MPFR_UNLIKELY (cache->inexact == 0))
                     {
                       if ((_sp[0] & _ulp) == 0)
                         {
                           inexact = -sign;
                           goto trunc_doit;
                         }
                       else
                         goto addoneulp;
                     }
                   else if (cache->inexact < 0)
                     goto addoneulp;
                   else /* cache->inexact > 0 */
                     {
                       inexact = -sign;
                       goto trunc_doit;
                     },
                   MPFR_EXP (dest) ++;
                   MPFR_ASSERTD (MPFR_EXP (dest) <= __gmpfr_emax);
                  );

  /* Rather a likely, this is a 100% success rate for
     all constants of MPFR */
  if (MPFR_LIKELY (cache->inexact != 0))
    {
      switch (rnd)
        {
        case MPFR_RNDZ:
        case MPFR_RNDD:
          if (MPFR_UNLIKELY (inexact == 0))
            {
              inexact = cache->inexact;
              if (inexact > 0)
                {
                  mpfr_nextbelow (dest);
                  inexact = -inexact;
                }
            }
          break;
        case MPFR_RNDU:
        case MPFR_RNDA:
          if (MPFR_UNLIKELY (inexact == 0))
            {
              inexact = cache->inexact;
              if (inexact < 0)
                {
                  mpfr_nextabove (dest);
                  inexact = -inexact;
                }
            }
          break;
        default: /* MPFR_RNDN */
          if (MPFR_UNLIKELY(inexact == 0))
            inexact = cache->inexact;
          break;
        }
    }

  MPFR_SAVE_EXPO_FREE (expo);

  /* Free the cache in read-only mode */
  MPFR_UNLOCK_READ(cache->lock);

  return mpfr_check_range (dest, inexact, rnd);
}