147 lines
4.4 KiB
C
147 lines
4.4 KiB
C
/* mpf_set_q (mpf_t rop, mpq_t op) -- Convert the rational op to the float rop.
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Copyright 1996, 1999, 2001, 2002, 2004, 2005 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include <stdio.h> /* for NULL */
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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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/* As usual the aim is to produce PREC(r) limbs, with the high non-zero.
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The basic mpn_tdiv_qr produces a quotient of nsize-dsize+1 limbs, with
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either the high or second highest limb non-zero. We arrange for
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nsize-dsize+1 to equal prec+1, hence giving either prec or prec+1 result
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limbs at PTR(r).
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nsize-dsize+1 == prec+1 is achieved by adjusting num(q), either dropping
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low limbs if it's too big, or padding with low zeros if it's too small.
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The full given den(q) is always used.
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We cannot truncate den(q), because even when it's much bigger than prec
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the last limbs can still influence the final quotient. Often they don't,
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but we leave optimization of that to a prospective quotient-only mpn
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division.
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Not done:
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If den(q) is a power of 2 then we may end up with low zero limbs on the
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result. But nothing is done about this, since it should be unlikely on
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random data, and can be left to an application to call mpf_div_2exp if it
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might occur with any frequency.
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Enhancements:
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The high quotient limb is non-zero when high{np,dsize} >= {dp,dsize}. We
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could make that comparison and use qsize==prec instead of qsize==prec+1,
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to save one limb in the division.
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Future:
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If/when mpn_tdiv_qr supports its qxn parameter we can use that instead of
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padding n with zeros in temporary space.
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If/when a quotient-only division exists it can be used here immediately.
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remp is only to satisfy mpn_tdiv_qr, the remainder is not used. */
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void
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mpf_set_q (mpf_t r, mpq_srcptr q)
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{
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mp_srcptr np, dp;
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mp_size_t prec, nsize, dsize, qsize, prospective_qsize, tsize, zeros;
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mp_size_t sign_quotient, high_zero;
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mp_ptr qp, tp, remp;
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mp_exp_t exp;
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TMP_DECL;
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ASSERT (SIZ(&q->_mp_den) > 0); /* canonical q */
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nsize = SIZ (&q->_mp_num);
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dsize = SIZ (&q->_mp_den);
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if (UNLIKELY (nsize == 0))
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{
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SIZ (r) = 0;
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EXP (r) = 0;
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return;
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}
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TMP_MARK;
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prec = PREC (r);
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qp = PTR (r);
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sign_quotient = nsize;
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nsize = ABS (nsize);
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np = PTR (&q->_mp_num);
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dp = PTR (&q->_mp_den);
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prospective_qsize = nsize - dsize + 1; /* q from using given n,d sizes */
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exp = prospective_qsize; /* ie. number of integer limbs */
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qsize = prec + 1; /* desired q */
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zeros = qsize - prospective_qsize; /* n zeros to get desired qsize */
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tsize = nsize + zeros; /* possible copy of n */
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if (WANT_TMP_DEBUG)
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{
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/* separate alloc blocks, for malloc debugging */
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remp = TMP_ALLOC_LIMBS (dsize);
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tp = NULL;
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if (zeros > 0)
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tp = TMP_ALLOC_LIMBS (tsize);
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}
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else
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{
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/* one alloc with a conditionalized size, for efficiency */
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mp_size_t size = dsize + (zeros > 0 ? tsize : 0);
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remp = TMP_ALLOC_LIMBS (size);
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tp = remp + dsize;
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}
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if (zeros > 0)
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{
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/* pad n with zeros into temporary space */
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MPN_ZERO (tp, zeros);
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MPN_COPY (tp+zeros, np, nsize);
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np = tp;
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nsize = tsize;
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}
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else
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{
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/* shorten n to get desired qsize */
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nsize += zeros;
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np -= zeros;
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}
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ASSERT (nsize-dsize+1 == qsize);
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mpn_tdiv_qr (qp, remp, (mp_size_t) 0, np, nsize, dp, dsize);
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/* strip possible zero high limb */
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high_zero = (qp[qsize-1] == 0);
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qsize -= high_zero;
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exp -= high_zero;
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EXP (r) = exp;
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SIZ (r) = sign_quotient >= 0 ? qsize : -qsize;
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TMP_FREE;
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}
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