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+/* mpf_set_q (mpf_t rop, mpq_t op) -- Convert the rational op to the float rop.
+
+Copyright 1996, 1999, 2001, 2002, 2004, 2005 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of either:
+
+ * 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.
+
+or
+
+ * the GNU General Public License as published by the Free Software
+ Foundation; either version 2 of the License, or (at your option) any
+ later version.
+
+or both in parallel, as here.
+
+The GNU MP 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 General Public License
+for more details.
+
+You should have received copies of the GNU General Public License and the
+GNU Lesser General Public License along with the GNU MP Library. If not,
+see https://www.gnu.org/licenses/. */
+
+#include <stdio.h> /* for NULL */
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+
+/* As usual the aim is to produce PREC(r) limbs, with the high non-zero.
+ The basic mpn_tdiv_qr produces a quotient of nsize-dsize+1 limbs, with
+ either the high or second highest limb non-zero. We arrange for
+ nsize-dsize+1 to equal prec+1, hence giving either prec or prec+1 result
+ limbs at PTR(r).
+
+ nsize-dsize+1 == prec+1 is achieved by adjusting num(q), either dropping
+ low limbs if it's too big, or padding with low zeros if it's too small.
+ The full given den(q) is always used.
+
+ We cannot truncate den(q), because even when it's much bigger than prec
+ the last limbs can still influence the final quotient. Often they don't,
+ but we leave optimization of that to a prospective quotient-only mpn
+ division.
+
+ Not done:
+
+ If den(q) is a power of 2 then we may end up with low zero limbs on the
+ result. But nothing is done about this, since it should be unlikely on
+ random data, and can be left to an application to call mpf_div_2exp if it
+ might occur with any frequency.
+
+ Enhancements:
+
+ The high quotient limb is non-zero when high{np,dsize} >= {dp,dsize}. We
+ could make that comparison and use qsize==prec instead of qsize==prec+1,
+ to save one limb in the division.
+
+ Future:
+
+ If/when mpn_tdiv_qr supports its qxn parameter we can use that instead of
+ padding n with zeros in temporary space.
+
+ If/when a quotient-only division exists it can be used here immediately.
+ remp is only to satisfy mpn_tdiv_qr, the remainder is not used. */
+
+void
+mpf_set_q (mpf_t r, mpq_srcptr q)
+{
+ mp_srcptr np, dp;
+ mp_size_t prec, nsize, dsize, qsize, prospective_qsize, tsize, zeros;
+ mp_size_t sign_quotient, high_zero;
+ mp_ptr qp, tp, remp;
+ mp_exp_t exp;
+ TMP_DECL;
+
+ ASSERT (SIZ(&q->_mp_den) > 0); /* canonical q */
+
+ nsize = SIZ (&q->_mp_num);
+ dsize = SIZ (&q->_mp_den);
+
+ if (UNLIKELY (nsize == 0))
+ {
+ SIZ (r) = 0;
+ EXP (r) = 0;
+ return;
+ }
+
+ TMP_MARK;
+
+ prec = PREC (r);
+ qp = PTR (r);
+
+ sign_quotient = nsize;
+ nsize = ABS (nsize);
+ np = PTR (&q->_mp_num);
+ dp = PTR (&q->_mp_den);
+
+ prospective_qsize = nsize - dsize + 1; /* q from using given n,d sizes */
+ exp = prospective_qsize; /* ie. number of integer limbs */
+ qsize = prec + 1; /* desired q */
+
+ zeros = qsize - prospective_qsize; /* n zeros to get desired qsize */
+ tsize = nsize + zeros; /* possible copy of n */
+
+ if (WANT_TMP_DEBUG)
+ {
+ /* separate alloc blocks, for malloc debugging */
+ remp = TMP_ALLOC_LIMBS (dsize);
+ tp = NULL;
+ if (zeros > 0)
+ tp = TMP_ALLOC_LIMBS (tsize);
+ }
+ else
+ {
+ /* one alloc with a conditionalized size, for efficiency */
+ mp_size_t size = dsize + (zeros > 0 ? tsize : 0);
+ remp = TMP_ALLOC_LIMBS (size);
+ tp = remp + dsize;
+ }
+
+ if (zeros > 0)
+ {
+ /* pad n with zeros into temporary space */
+ MPN_ZERO (tp, zeros);
+ MPN_COPY (tp+zeros, np, nsize);
+ np = tp;
+ nsize = tsize;
+ }
+ else
+ {
+ /* shorten n to get desired qsize */
+ nsize += zeros;
+ np -= zeros;
+ }
+
+ ASSERT (nsize-dsize+1 == qsize);
+ mpn_tdiv_qr (qp, remp, (mp_size_t) 0, np, nsize, dp, dsize);
+
+ /* strip possible zero high limb */
+ high_zero = (qp[qsize-1] == 0);
+ qsize -= high_zero;
+ exp -= high_zero;
+
+ EXP (r) = exp;
+ SIZ (r) = sign_quotient >= 0 ? qsize : -qsize;
+
+ TMP_FREE;
+}