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/* mpfr_cache -- cache interface for multiple-precision constants in MPFR.
Copyright 2004-2021 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);
}
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