1 /* mpfr_round_p -- check if an approximation is roundable.
3 Copyright 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
4 Contributed by the Arenaire and Cacao projects, INRIA.
6 This file is part of the GNU MPFR Library.
8 The GNU MPFR Library is free software; you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 2.1 of the License, or (at your
11 option) any later version.
13 The GNU MPFR Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
16 License for more details.
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MPFR Library; see the file COPYING.LIB. If not, write to
20 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
21 MA 02110-1301, USA. */
23 #include "mpfr-impl.h"
25 /* Check against mpfr_can_round ? */
28 int mpfr_round_p_2 (mp_limb_t
*, mp_size_t
, mp_exp_t
, mp_prec_t
);
30 mpfr_round_p (mp_limb_t
*bp
, mp_size_t bn
, mp_exp_t err0
, mp_prec_t prec
)
34 i1
= mpfr_round_p_2 (bp
, bn
, err0
, prec
);
35 i2
= mpfr_can_round_raw (bp
, bn
, MPFR_SIGN_POS
, err0
,
36 GMP_RNDN
, GMP_RNDZ
, prec
);
39 fprintf (stderr
, "mpfr_round_p(%d) != mpfr_can_round(%d)!\n"
40 "bn = %lu, err0 = %ld, prec = %lu\nbp = ", i1
, i2
,
41 (unsigned long) bn
, (long) err0
, (unsigned long) prec
);
42 gmp_fprintf (stderr
, "%NX\n", bp
, bn
);
47 # define mpfr_round_p mpfr_round_p_2
52 * Assuming {bp, bn} is an approximation of a non-singular number
53 * with error at most equal to 2^(EXP(b)-err0) (`err0' bits of b are known)
54 * of direction unknown, check if we can round b toward zero with
58 mpfr_round_p (mp_limb_t
*bp
, mp_size_t bn
, mp_exp_t err0
, mp_prec_t prec
)
65 err
= (mp_prec_t
) bn
* BITS_PER_MP_LIMB
;
66 if (MPFR_UNLIKELY (err0
<= 0 || (mpfr_uexp_t
) err0
<= prec
|| prec
>= err
))
67 return 0; /* can't round */
68 err
= MIN (err
, (mpfr_uexp_t
) err0
);
70 k
= prec
/ BITS_PER_MP_LIMB
;
71 s
= BITS_PER_MP_LIMB
- prec
%BITS_PER_MP_LIMB
;
72 n
= err
/ BITS_PER_MP_LIMB
- k
;
74 MPFR_ASSERTD (n
>= 0);
75 MPFR_ASSERTD (bn
> k
);
77 /* Check first limb */
80 mask
= s
== BITS_PER_MP_LIMB
? MP_LIMB_T_MAX
: MPFR_LIMB_MASK (s
);
83 if (MPFR_LIKELY (n
== 0))
85 /* prec and error are in the same limb */
86 s
= BITS_PER_MP_LIMB
- err
% BITS_PER_MP_LIMB
;
87 MPFR_ASSERTD (s
< BITS_PER_MP_LIMB
);
90 return tmp
!= 0 && tmp
!= mask
;
92 else if (MPFR_UNLIKELY (tmp
== 0))
94 /* Check if all (n-1) limbs are 0 */
98 /* Check if final error limb is 0 */
99 s
= BITS_PER_MP_LIMB
- err
% BITS_PER_MP_LIMB
;
100 if (s
== BITS_PER_MP_LIMB
)
105 else if (MPFR_UNLIKELY (tmp
== mask
))
107 /* Check if all (n-1) limbs are 11111111111111111 */
109 if (*bp
-- != MP_LIMB_T_MAX
)
111 /* Check if final error limb is 0 */
112 s
= BITS_PER_MP_LIMB
- err
% BITS_PER_MP_LIMB
;
113 if (s
== BITS_PER_MP_LIMB
)
116 return tmp
!= (MP_LIMB_T_MAX
>> s
);
120 /* First limb is different from 000000 or 1111111 */