OpenXM_contrib/gmp/mpf/set_q.c - diff

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Diff for /OpenXM_contrib/gmp/mpf/Attic/set_q.c between version 1.1.1.1 and 1.1.1.3

version 1.1.1.1, 2000/01/10 15:35:22

version 1.1.1.3, 2003/08/25 16:06:34

Line 1

/* mpf_set_q (mpf_t rop, mpq_t op) -- Convert the rational op to the float rop.

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 the GNU Library General Public License as published by

it under the terms of the GNU Lesser General Public License as published by

the Free Software Foundation; either version 2 of the License, or (at your

the Free Software Foundation; either version 2.1 of the License, or (at your

option) any later version.

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 Library General Public

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 Library General Public License

You should have received a copy of the GNU Lesser General Public License

along with the GNU MP Library; see the file COPYING.LIB. If not, write to

the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,

MA 02111-1307, USA. */

Line 23 MA 02111-1307, USA. */

#include "gmp-impl.h"

#include "longlong.h"

/* Algorithm:

1. Develop >= n bits of src.num / src.den, where n is the number of bits

in a double. This (partial) division will use all bits from the

denominator.

2. Use the remainder to determine how to round the result.

3. Assign the integral result to a temporary double.

4. Scale the temporary double, and return the result.

An alternative algorithm, that would be faster:

0. Let n be somewhat larger than the number of significant bits in a double.

1. Extract the most significant n bits of the denominator, and an equal

number of bits from the numerator.

2. Interpret the extracted numbers as integers, call them a and b

respectively, and develop n bits of the fractions ((a + 1) / b) and

(a / (b + 1)) using mpn_divrem.

3. If the computed values are identical UP TO THE POSITION WE CARE ABOUT,

we are done. If they are different, repeat the algorithm from step 1,

but first let n = n * 2.

4. If we end up using all bits from the numerator and denominator, fall

back to the first algorithm above.

5. Just to make life harder, The computation of a + 1 and b + 1 above

might give carry-out... Needs special handling. It might work to

subtract 1 in both cases instead.

void

#if __STDC__

mpf_set_q (mpf_t r, mpq_srcptr q)

#else

mpf_set_q (r, q)

mpf_t r;

mpq_srcptr q;

#endif

{

mp_ptr np, dp;

mp_ptr rp;

mp_size_t nsize, dsize;

mp_size_t qsize, rsize;

mp_size_t sign_quotient;

unsigned normalization_steps;

mp_limb_t qlimb;

mp_ptr qp;

mp_size_t prec;

Line 107 mpf_set_q (r, q)

Line 75 mpf_set_q (r, q)

rsize = MAX (nsize, dsize);

rp = (mp_ptr) TMP_ALLOC ((rsize + 1) * BYTES_PER_MP_LIMB);

count_leading_zeros (normalization_steps, dp[dsize - 1]);

/* Normalize the denominator, i.e. make its most significant bit set by

shifting it NORMALIZATION_STEPS bits to the left. Also shift the

numerator the same number of steps (to keep the quotient the same!). */

if (normalization_steps != 0)

if ((dp[dsize - 1] & GMP_NUMB_HIGHBIT) == 0)

{

mp_ptr tp;

mp_limb_t nlimb;

unsigned normalization_steps;

count_leading_zeros (normalization_steps, dp[dsize - 1]);

normalization_steps -= GMP_NAIL_BITS;

/* Shift up the denominator setting the most significant bit of

the most significant limb. Use temporary storage not to clobber

the original contents of the denominator. */

Line 132 mpf_set_q (r, q)

Line 102 mpf_set_q (r, q)

}

else

{

nlimb = mpn_lshift (rp, np, nsize, normalization_steps);

nlimb = mpn_lshift (rp, np, rsize, normalization_steps);

}

if (nlimb != 0)

{

rp[rsize] = nlimb;

rsize++;

exp++;

/* Don't just increase rsize, chop off rp at the low end instead. */

if (rsize == prec)

rp++;

else

rsize++;

}

else

Line 164 mpf_set_q (r, q)

Line 138 mpf_set_q (r, q)

}

EXP (r) = exp;

SIZ (r) = qsize;

SIZ (r) = sign_quotient >= 0 ? qsize : -qsize;

TMP_FREE (marker);

}

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