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Diffstat (limited to 'src/round_raw_generic.c')
| -rw-r--r-- | src/round_raw_generic.c | 259 |
1 files changed, 259 insertions, 0 deletions
diff --git a/src/round_raw_generic.c b/src/round_raw_generic.c new file mode 100644 index 0000000..79ba90d --- /dev/null +++ b/src/round_raw_generic.c @@ -0,0 +1,259 @@ +/* mpfr_round_raw_generic -- Generic rounding function + +Copyright 1999, 2000, 2001, 2002, 2003, 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. */ + +#ifndef flag +# error "ERROR: flag must be defined (0 / 1)" +#endif +#ifndef use_inexp +# error "ERROR: use_enexp must be defined (0 / 1)" +#endif +#ifndef mpfr_round_raw_generic +# error "ERROR: mpfr_round_raw_generic must be defined" +#endif + +/* + * If flag = 0, puts in y the value of xp (with precision xprec and + * sign 1 if negative=0, -1 otherwise) rounded to precision yprec and + * direction rnd_mode. Supposes x is not zero nor NaN nor +/- Infinity + * (i.e. *xp != 0). In that case, the return value is a possible carry + * (0 or 1) that may happen during the rounding, in which case the result + * is a power of two. + * + * If inexp != NULL, put in *inexp the inexact flag of the rounding (0, 1, -1). + * In case of even rounding when rnd = MPFR_RNDN, put MPFR_EVEN_INEX (2) or + * -MPFR_EVEN_INEX (-2) in *inexp. + * + * If flag = 1, just returns whether one should add 1 or not for rounding. + * + * Note: yprec may be < MPFR_PREC_MIN; in particular, it may be equal + * to 1. In this case, the even rounding is done away from 0, which is + * a natural generalization. Indeed, a number with 1-bit precision can + * be seen as a denormalized number with more precision. + */ + +int +mpfr_round_raw_generic( +#if flag == 0 + mp_limb_t *yp, +#endif + const mp_limb_t *xp, mpfr_prec_t xprec, + int neg, mpfr_prec_t yprec, mpfr_rnd_t rnd_mode +#if use_inexp != 0 + , int *inexp +#endif + ) +{ + mp_size_t xsize, nw; + mp_limb_t himask, lomask, sb; + int rw; +#if flag == 0 + int carry; +#endif +#if use_inexp == 0 + int *inexp; +#endif + + if (use_inexp) + MPFR_ASSERTD(inexp != ((int*) 0)); + MPFR_ASSERTD(neg == 0 || neg == 1); + + if (flag && !use_inexp && + (xprec <= yprec || MPFR_IS_LIKE_RNDZ (rnd_mode, neg))) + return 0; + + xsize = MPFR_PREC2LIMBS (xprec); + nw = yprec / GMP_NUMB_BITS; + rw = yprec & (GMP_NUMB_BITS - 1); + + if (MPFR_UNLIKELY(xprec <= yprec)) + { /* No rounding is necessary. */ + /* if yp=xp, maybe an overlap: MPN_COPY_DECR is ok when src <= dst */ + if (MPFR_LIKELY(rw)) + nw++; + MPFR_ASSERTD(nw >= 1); + MPFR_ASSERTD(nw >= xsize); + if (use_inexp) + *inexp = 0; +#if flag == 0 + MPN_COPY_DECR(yp + (nw - xsize), xp, xsize); + MPN_ZERO(yp, nw - xsize); +#endif + return 0; + } + + if (use_inexp || !MPFR_IS_LIKE_RNDZ(rnd_mode, neg)) + { + mp_size_t k = xsize - nw - 1; + + if (MPFR_LIKELY(rw)) + { + nw++; + lomask = MPFR_LIMB_MASK (GMP_NUMB_BITS - rw); + himask = ~lomask; + } + else + { + lomask = ~(mp_limb_t) 0; + himask = ~(mp_limb_t) 0; + } + MPFR_ASSERTD(k >= 0); + sb = xp[k] & lomask; /* First non-significant bits */ + /* Rounding to nearest ? */ + if (MPFR_LIKELY( rnd_mode == MPFR_RNDN) ) + { + /* Rounding to nearest */ + mp_limb_t rbmask = MPFR_LIMB_ONE << (GMP_NUMB_BITS - 1 - rw); + if (sb & rbmask) /* rounding bit */ + sb &= ~rbmask; /* it is 1, clear it */ + else + { + /* Rounding bit is 0, behave like rounding to 0 */ + goto rnd_RNDZ; + } + while (MPFR_UNLIKELY(sb == 0) && k > 0) + sb = xp[--k]; + /* rounding to nearest, with rounding bit = 1 */ + if (MPFR_UNLIKELY(sb == 0)) /* Even rounding. */ + { + /* sb == 0 && rnd_mode == MPFR_RNDN */ + sb = xp[xsize - nw] & (himask ^ (himask << 1)); + if (sb == 0) + { + if (use_inexp) + *inexp = 2*MPFR_EVEN_INEX*neg-MPFR_EVEN_INEX; + /* ((neg!=0)^(sb!=0)) ? MPFR_EVEN_INEX : -MPFR_EVEN_INEX;*/ + /* Since neg = 0 or 1 and sb=0*/ +#if flag == 1 + return 0 /*sb != 0 && rnd_mode != MPFR_RNDZ */; +#else + MPN_COPY_INCR(yp, xp + xsize - nw, nw); + yp[0] &= himask; + return 0; +#endif + } + else + { + /* sb != 0 && rnd_mode == MPFR_RNDN */ + if (use_inexp) + *inexp = MPFR_EVEN_INEX-2*MPFR_EVEN_INEX*neg; + /*((neg!=0)^(sb!=0))? MPFR_EVEN_INEX : -MPFR_EVEN_INEX; */ + /*Since neg= 0 or 1 and sb != 0 */ + goto rnd_RNDN_add_one_ulp; + } + } + else /* sb != 0 && rnd_mode == MPFR_RNDN*/ + { + if (use_inexp) + /* *inexp = (neg == 0) ? 1 : -1; but since neg = 0 or 1 */ + *inexp = 1-2*neg; + rnd_RNDN_add_one_ulp: +#if flag == 1 + return 1; /*sb != 0 && rnd_mode != MPFR_RNDZ;*/ +#else + carry = mpn_add_1 (yp, xp + xsize - nw, nw, + rw ? + MPFR_LIMB_ONE << (GMP_NUMB_BITS - rw) + : MPFR_LIMB_ONE); + yp[0] &= himask; + return carry; +#endif + } + } + /* Rounding to Zero ? */ + else if (MPFR_IS_LIKE_RNDZ(rnd_mode, neg)) + { + /* rnd_mode == MPFR_RNDZ */ + rnd_RNDZ: + while (MPFR_UNLIKELY(sb == 0) && k > 0) + sb = xp[--k]; + if (use_inexp) + /* rnd_mode == MPFR_RNDZ and neg = 0 or 1 */ + /* (neg != 0) ^ (rnd_mode != MPFR_RNDZ)) ? 1 : -1);*/ + *inexp = MPFR_UNLIKELY(sb == 0) ? 0 : (2*neg-1); +#if flag == 1 + return 0; /*sb != 0 && rnd_mode != MPFR_RNDZ;*/ +#else + MPN_COPY_INCR(yp, xp + xsize - nw, nw); + yp[0] &= himask; + return 0; +#endif + } + else + { + /* rnd_mode = Away */ + while (MPFR_UNLIKELY(sb == 0) && k > 0) + sb = xp[--k]; + if (MPFR_UNLIKELY(sb == 0)) + { + /* sb = 0 && rnd_mode != MPFR_RNDZ */ + if (use_inexp) + /* (neg != 0) ^ (rnd_mode != MPFR_RNDZ)) ? 1 : -1);*/ + *inexp = 0; +#if flag == 1 + return 0; +#else + MPN_COPY_INCR(yp, xp + xsize - nw, nw); + yp[0] &= himask; + return 0; +#endif + } + else + { + /* sb != 0 && rnd_mode != MPFR_RNDZ */ + if (use_inexp) + /* (neg != 0) ^ (rnd_mode != MPFR_RNDZ)) ? 1 : -1);*/ + *inexp = 1-2*neg; +#if flag == 1 + return 1; +#else + carry = mpn_add_1(yp, xp + xsize - nw, nw, + rw ? MPFR_LIMB_ONE << (GMP_NUMB_BITS - rw) + : 1); + yp[0] &= himask; + return carry; +#endif + } + } + } + else + { + /* Roundind mode = Zero / No inexact flag */ +#if flag == 1 + return 0 /*sb != 0 && rnd_mode != MPFR_RNDZ*/; +#else + if (MPFR_LIKELY(rw)) + { + nw++; + himask = ~MPFR_LIMB_MASK (GMP_NUMB_BITS - rw); + } + else + himask = ~(mp_limb_t) 0; + MPN_COPY_INCR(yp, xp + xsize - nw, nw); + yp[0] &= himask; + return 0; +#endif + } +} + +#undef flag +#undef use_inexp +#undef mpfr_round_raw_generic |