mod_1.c
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- /* UltraSPARC 64 mpn_mod_1 -- mpn by limb remainder.
- Copyright 1991, 1993, 1994, 1999, 2000, 2001, 2003 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"
- #include "longlong.h"
- #include "mpn/sparc64/sparc64.h"
- /* 64-bit divisor 32-bit divisor
- cycles/limb cycles/limb
- (approx) (approx)
- Ultrasparc 2i: 160 120
- */
- /* 32-bit divisors are treated in special case code. This requires 4 mulx
- per limb instead of 8 in the general case.
- For big endian systems we need HALF_ENDIAN_ADJ included in the src[i]
- addressing, to get the two halves of each limb read in the correct order.
- This is kept in an adj variable. Doing that measures about 6 c/l faster
- than just writing HALF_ENDIAN_ADJ(i) in the loop. The latter shouldn't
- be 6 cycles worth of work, but perhaps it doesn't schedule well (on gcc
- 3.2.1 at least).
- A simple udivx/umulx loop for the 32-bit case was attempted for small
- sizes, but at size==2 it was only about the same speed and at size==3 was
- slower. */
- mp_limb_t
- mpn_mod_1 (mp_srcptr src_limbptr, mp_size_t size_limbs, mp_limb_t d_limb)
- {
- int norm, norm_rshift;
- mp_limb_t src_high_limb;
- mp_size_t i;
- ASSERT (size_limbs >= 0);
- ASSERT (d_limb != 0);
- if (UNLIKELY (size_limbs == 0))
- return 0;
- src_high_limb = src_limbptr[size_limbs-1];
- /* udivx is good for size==1, and no need to bother checking limb<divisor,
- since if that's likely the caller should check */
- if (UNLIKELY (size_limbs == 1))
- return src_high_limb % d_limb;
- if (d_limb <= CNST_LIMB(0xFFFFFFFF))
- {
- unsigned *src, n1, n0, r, dummy_q, nshift, norm_rmask;
- mp_size_t size, adj;
- mp_limb_t dinv_limb;
- size = 2 * size_limbs; /* halfwords */
- src = (unsigned *) src_limbptr;
- /* prospective initial remainder, if < d */
- r = src_high_limb >> 32;
- /* If the length of the source is uniformly distributed, then there's
- a 50% chance of the high 32-bits being zero, which we can skip. */
- if (r == 0)
- {
- r = (unsigned) src_high_limb;
- size--;
- ASSERT (size > 0); /* because always even */
- }
- /* Skip a division if high < divisor. Having the test here before
- normalizing will still skip as often as possible. */
- if (r < d_limb)
- {
- size--;
- ASSERT (size > 0); /* because size==1 handled above */
- }
- else
- r = 0;
- count_leading_zeros_32 (norm, d_limb);
- norm -= 32;
- d_limb <<= norm;
- norm_rshift = 32 - norm;
- norm_rmask = (norm == 0 ? 0 : 0xFFFFFFFF);
- i = size-1;
- adj = HALF_ENDIAN_ADJ (i);
- n1 = src [i + adj];
- r = (r << norm) | ((n1 >> norm_rshift) & norm_rmask);
- invert_half_limb (dinv_limb, d_limb);
- adj = -adj;
- for (i--; i >= 0; i--)
- {
- n0 = src [i + adj];
- adj = -adj;
- nshift = (n1 << norm) | ((n0 >> norm_rshift) & norm_rmask);
- udiv_qrnnd_half_preinv (dummy_q, r, r, nshift, d_limb, dinv_limb);
- n1 = n0;
- }
- /* same as loop, but without n0 */
- nshift = n1 << norm;
- udiv_qrnnd_half_preinv (dummy_q, r, r, nshift, d_limb, dinv_limb);
- ASSERT ((r & ((1 << norm) - 1)) == 0);
- return r >> norm;
- }
- else
- {
- mp_srcptr src;
- mp_size_t size;
- mp_limb_t n1, n0, r, dinv, dummy_q, nshift, norm_rmask;
- src = src_limbptr;
- size = size_limbs;
- r = src_high_limb; /* initial remainder */
- /* Skip a division if high < divisor. Having the test here before
- normalizing will still skip as often as possible. */
- if (r < d_limb)
- {
- size--;
- ASSERT (size > 0); /* because size==1 handled above */
- }
- else
- r = 0;
- count_leading_zeros (norm, d_limb);
- d_limb <<= norm;
- norm_rshift = GMP_LIMB_BITS - norm;
- norm_rmask = (norm == 0 ? 0 : 0xFFFFFFFF);
- src += size;
- n1 = *--src;
- r = (r << norm) | ((n1 >> norm_rshift) & norm_rmask);
- invert_limb (dinv, d_limb);
- for (i = size-2; i >= 0; i--)
- {
- n0 = *--src;
- nshift = (n1 << norm) | ((n0 >> norm_rshift) & norm_rmask);
- udiv_qrnnd_preinv (dummy_q, r, r, nshift, d_limb, dinv);
- n1 = n0;
- }
- /* same as loop, but without n0 */
- nshift = n1 << norm;
- udiv_qrnnd_preinv (dummy_q, r, r, nshift, d_limb, dinv);
- ASSERT ((r & ((CNST_LIMB(1) << norm) - 1)) == 0);
- return r >> norm;
- }
- }