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/* mpf_get_ui -- mpf to ulong conversion
Copyright 2001, 2002, 2004 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 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 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 Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
#include "gmp.h"
#include "gmp-impl.h"
/* Any fraction bits are truncated, meaning simply discarded.
For values bigger than a ulong, the low bits are returned (the low
absolute value bits actually), like mpz_get_ui, but this isn't
documented.
Notice this is equivalent to mpz_set_f + mpz_get_ui.
Implementation:
The limb just above the radix point for us to extract is ptr[size-exp].
We need to check that the size-exp index falls in our available data
range, 0 to size-1 inclusive. We test this without risk of an overflow
involving exp by requiring size>=exp (giving size-exp >= 0) and exp>0
(giving size-exp <= size-1).
Notice if size==0 there's no fetch, since of course size>=exp and exp>0
can only be true if size>0. So there's no special handling for size==0,
it comes out as 0 the same as any other time we have no data at our
target index.
For nails, the second limb above the radix point is also required, this
is ptr[size-exp+1].
Again we need to check that size-exp+1 falls in our data range, 0 to
size-1 inclusive. We test without risk of overflow by requiring
size+1>=exp (giving size-exp+1 >= 0) and exp>1 (giving size-exp+1 <=
size-1).
And again if size==0 these second fetch conditions are not satisfied
either since size+1>=exp and exp>1 are only true if size>0.
The code is arranged with exp>0 wrapping the exp>1 test since exp>1 is
mis-compiled by alpha gcc prior to version 3.4. It re-writes it as
exp-1>0, which is incorrect when exp==MP_EXP_T_MIN. By having exp>0
tested first we ensure MP_EXP_T_MIN doesn't reach exp>1. */
unsigned long
mpf_get_ui (mpf_srcptr f)
{
mp_size_t size;
mp_exp_t exp;
mp_srcptr fp;
mp_limb_t fl;
exp = EXP (f);
size = SIZ (f);
fp = PTR (f);
fl = 0;
if (exp > 0)
{
/* there are some limbs above the radix point */
size = ABS (size);
if (size >= exp)
fl = fp[size-exp];
#if BITS_PER_ULONG > GMP_NUMB_BITS
if (exp > 1 && size+1 >= exp)
fl += (fp[size-exp+1] << GMP_NUMB_BITS);
#endif
}
return (unsigned long) fl;
}
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