150 lines
4.2 KiB
C
150 lines
4.2 KiB
C
/* UltraSPARC 64 mpn_divexact_1 -- mpn by limb exact division.
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THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY. THEY'RE ALMOST
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CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN
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FUTURE GNU MP RELEASES.
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Copyright 2000, 2001, 2003 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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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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#include "mpn/sparc64/sparc64.h"
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/* 64-bit divisor 32-bit divisor
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cycles/limb cycles/limb
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(approx) (approx)
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Ultrasparc 2i: 110 70
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*/
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/* There are two key ideas here to reduce mulx's. Firstly when the divisor
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is 32-bits the high of q*d can be calculated without the two 32x32->64
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cross-products involving the high 32-bits of the divisor, that being zero
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of course. Secondly umul_ppmm_lowequal and umul_ppmm_half_lowequal save
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one mulx (each) knowing the low of q*d is equal to the input limb l.
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For size==1, a simple udivx is used. This is faster than calculating an
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inverse.
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For a 32-bit divisor and small sizes, an attempt was made at a simple
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udivx loop (two per 64-bit limb), but it turned out to be slower than
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mul-by-inverse. At size==2 the inverse is about 260 cycles total
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compared to a udivx at 291. Perhaps the latter would suit when size==2
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but the high 32-bits of the second limb is zero (saving one udivx), but
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it doesn't seem worth a special case just for that. */
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void
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mpn_divexact_1 (mp_ptr dst, mp_srcptr src, mp_size_t size, mp_limb_t divisor)
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{
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mp_limb_t inverse, s, s_next, c, l, ls, q;
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unsigned rshift, lshift;
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mp_limb_t lshift_mask;
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mp_limb_t divisor_h;
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ASSERT (size >= 1);
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ASSERT (divisor != 0);
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ASSERT (MPN_SAME_OR_SEPARATE_P (dst, src, size));
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ASSERT_MPN (src, size);
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ASSERT_LIMB (divisor);
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s = *src++; /* src low limb */
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size--;
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if (size == 0)
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{
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*dst = s / divisor;
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return;
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}
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if ((divisor & 1) == 0)
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{
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count_trailing_zeros (rshift, divisor);
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divisor >>= rshift;
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}
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else
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rshift = 0;
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modlimb_invert (inverse, divisor);
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lshift = 64 - rshift;
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/* lshift==64 means no shift, so must mask out other part in this case */
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lshift_mask = (rshift == 0 ? 0 : MP_LIMB_T_MAX);
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c = 0;
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divisor_h = HIGH32 (divisor);
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if (divisor_h == 0)
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{
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/* 32-bit divisor */
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do
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{
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s_next = *src++;
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ls = (s >> rshift) | ((s_next << lshift) & lshift_mask);
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s = s_next;
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SUBC_LIMB (c, l, ls, c);
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q = l * inverse;
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*dst++ = q;
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umul_ppmm_half_lowequal (l, q, divisor, l);
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c += l;
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size--;
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}
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while (size != 0);
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ls = s >> rshift;
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l = ls - c;
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q = l * inverse;
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*dst = q;
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}
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else
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{
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/* 64-bit divisor */
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mp_limb_t divisor_l = LOW32 (divisor);
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do
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{
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s_next = *src++;
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ls = (s >> rshift) | ((s_next << lshift) & lshift_mask);
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s = s_next;
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SUBC_LIMB (c, l, ls, c);
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q = l * inverse;
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*dst++ = q;
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umul_ppmm_lowequal (l, q, divisor, divisor_h, divisor_l, l);
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c += l;
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size--;
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}
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while (size != 0);
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ls = s >> rshift;
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l = ls - c;
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q = l * inverse;
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*dst = q;
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}
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}
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