105 lines
2.7 KiB
C
105 lines
2.7 KiB
C
/* mpn_mod_1(dividend_ptr, dividend_size, divisor_limb) --
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Divide (DIVIDEND_PTR,,DIVIDEND_SIZE) by DIVISOR_LIMB.
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Return the single-limb remainder.
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There are no constraints on the value of the divisor.
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QUOT_PTR and DIVIDEND_PTR might point to the same limb.
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Copyright (C) 1991, 1992 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 General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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The GNU MP Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with the GNU MP Library; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
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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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mp_limb
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#ifdef __STDC__
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mpn_mod_1 (mp_srcptr dividend_ptr, mp_size dividend_size,
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unsigned long int divisor_limb)
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#else
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mpn_mod_1 (dividend_ptr, dividend_size, divisor_limb)
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mp_srcptr dividend_ptr;
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mp_size dividend_size;
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unsigned long int divisor_limb;
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#endif
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{
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int normalization_steps;
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mp_size i;
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mp_limb n1, n0, r;
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int dummy;
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/* Botch: Should this be handled at all? Rely on callers? */
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if (dividend_size == 0)
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return 0;
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if (UDIV_NEEDS_NORMALIZATION)
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{
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count_leading_zeros (normalization_steps, divisor_limb);
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if (normalization_steps != 0)
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{
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divisor_limb <<= normalization_steps;
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n1 = dividend_ptr[dividend_size - 1];
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r = n1 >> (BITS_PER_MP_LIMB - normalization_steps);
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/* Possible optimization:
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if (r == 0
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&& divisor_limb > ((n1 << normalization_steps)
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| (dividend_ptr[dividend_size - 2] >> ...)))
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...one division less...
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*/
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for (i = dividend_size - 2; i >= 0; i--)
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{
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n0 = dividend_ptr[i];
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udiv_qrnnd (dummy, r, r,
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((n1 << normalization_steps)
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| (n0 >> (BITS_PER_MP_LIMB - normalization_steps))),
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divisor_limb);
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n1 = n0;
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}
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udiv_qrnnd (dummy, r, r,
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n1 << normalization_steps,
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divisor_limb);
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return r >> normalization_steps;
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}
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}
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/* No normalization needed, either because udiv_qrnnd doesn't require
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it, or because DIVISOR_LIMB is already normalized. */
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i = dividend_size - 1;
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r = dividend_ptr[i];
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if (r >= divisor_limb)
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{
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r = 0;
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}
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else
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{
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i--;
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}
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for (; i >= 0; i--)
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{
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n0 = dividend_ptr[i];
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udiv_qrnnd (dummy, r, r, n0, divisor_limb);
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}
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return r;
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}
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