80 lines
2.3 KiB
C
80 lines
2.3 KiB
C
/* mpf_get_si -- mpf to long conversion
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Copyright 2001, 2002, 2004 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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*/
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#include "gmp.h"
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#include "gmp-impl.h"
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/* Any fraction bits are truncated, meaning simply discarded.
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For values bigger than a long, the low bits are returned, like
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mpz_get_si, but this isn't documented.
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Notice this is equivalent to mpz_set_f + mpz_get_si.
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Implementation:
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fl is established in basically the same way as for mpf_get_ui, see that
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code for explanations of the conditions.
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However unlike mpf_get_ui we need an explicit return 0 for exp<=0. When
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f is a negative fraction (ie. size<0 and exp<=0) we can't let fl==0 go
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through to the zany final "~ ((fl - 1) & LONG_MAX)", that would give
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-0x80000000 instead of the desired 0. */
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long
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mpf_get_si (mpf_srcptr f)
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{
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mp_exp_t exp;
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mp_size_t size, abs_size;
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mp_srcptr fp;
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mp_limb_t fl;
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exp = EXP (f);
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size = SIZ (f);
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fp = PTR (f);
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/* fraction alone truncates to zero
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this also covers zero, since we have exp==0 for zero */
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if (exp <= 0)
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return 0L;
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/* there are some limbs above the radix point */
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fl = 0;
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abs_size = ABS (size);
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if (abs_size >= exp)
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fl = fp[abs_size-exp];
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#if BITS_PER_ULONG > GMP_NUMB_BITS
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if (exp > 1 && abs_size+1 >= exp)
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fl |= fp[abs_size - exp + 1] << GMP_NUMB_BITS;
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#endif
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if (size > 0)
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return fl & LONG_MAX;
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else
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/* this form necessary to correctly handle -0x80..00 */
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return ~ ((fl - 1) & LONG_MAX);
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}
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