1 /* mpfr_round_p -- check if an approximation is roundable. 2 3 Copyright 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc. 4 Contributed by the Arenaire and Caramel projects, INRIA. 5 6 This file is part of the GNU MPFR Library. 7 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 3 of the License, or (at your 11 option) any later version. 12 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. 17 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.LESSER. If not, see 20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ 22 23 #include "mpfr-impl.h" 24 25 /* Check against mpfr_can_round? */ 26 #ifdef WANT_ASSERT 27 # if WANT_ASSERT >= 2 28 int mpfr_round_p_2 (mp_limb_t *, mp_size_t, mpfr_exp_t, mpfr_prec_t); 29 int 30 mpfr_round_p (mp_limb_t *bp, mp_size_t bn, mpfr_exp_t err0, mpfr_prec_t prec) 31 { 32 int i1, i2; 33 34 i1 = mpfr_round_p_2 (bp, bn, err0, prec); 35 i2 = mpfr_can_round_raw (bp, bn, MPFR_SIGN_POS, err0, 36 MPFR_RNDN, MPFR_RNDZ, prec); 37 if (i1 != i2) 38 { 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); 43 MPFR_ASSERTN (0); 44 } 45 return i1; 46 } 47 # define mpfr_round_p mpfr_round_p_2 48 # endif 49 #endif 50 51 /* 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 55 * precision prec. 56 */ 57 int 58 mpfr_round_p (mp_limb_t *bp, mp_size_t bn, mpfr_exp_t err0, mpfr_prec_t prec) 59 { 60 mpfr_prec_t err; 61 mp_size_t k, n; 62 mp_limb_t tmp, mask; 63 int s; 64 65 err = (mpfr_prec_t) bn * GMP_NUMB_BITS; 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); 69 70 k = prec / GMP_NUMB_BITS; 71 s = GMP_NUMB_BITS - prec%GMP_NUMB_BITS; 72 n = err / GMP_NUMB_BITS - k; 73 74 MPFR_ASSERTD (n >= 0); 75 MPFR_ASSERTD (bn > k); 76 77 /* Check first limb */ 78 bp += bn-1-k; 79 tmp = *bp--; 80 mask = s == GMP_NUMB_BITS ? MP_LIMB_T_MAX : MPFR_LIMB_MASK (s); 81 tmp &= mask; 82 83 if (MPFR_LIKELY (n == 0)) 84 { 85 /* prec and error are in the same limb */ 86 s = GMP_NUMB_BITS - err % GMP_NUMB_BITS; 87 MPFR_ASSERTD (s < GMP_NUMB_BITS); 88 tmp >>= s; 89 mask >>= s; 90 return tmp != 0 && tmp != mask; 91 } 92 else if (MPFR_UNLIKELY (tmp == 0)) 93 { 94 /* Check if all (n-1) limbs are 0 */ 95 while (--n) 96 if (*bp-- != 0) 97 return 1; 98 /* Check if final error limb is 0 */ 99 s = GMP_NUMB_BITS - err % GMP_NUMB_BITS; 100 if (s == GMP_NUMB_BITS) 101 return 0; 102 tmp = *bp >> s; 103 return tmp != 0; 104 } 105 else if (MPFR_UNLIKELY (tmp == mask)) 106 { 107 /* Check if all (n-1) limbs are 11111111111111111 */ 108 while (--n) 109 if (*bp-- != MP_LIMB_T_MAX) 110 return 1; 111 /* Check if final error limb is 0 */ 112 s = GMP_NUMB_BITS - err % GMP_NUMB_BITS; 113 if (s == GMP_NUMB_BITS) 114 return 0; 115 tmp = *bp >> s; 116 return tmp != (MP_LIMB_T_MAX >> s); 117 } 118 else 119 { 120 /* First limb is different from 000000 or 1111111 */ 121 return 1; 122 } 123 } 124