dive_1.c
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上传日期:2022-08-06
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- /* Alpha mpn_divexact_1 -- mpn by limb exact division.
- THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY. THEY'RE ALMOST
- CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN
- FUTURE GNU MP RELEASES.
- Copyright 2000, 2001, 2002, 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"
- /* cycles/limb
- EV4: 47.0
- EV5: 30.0
- EV6: 15.0
- */
- /* The dependent chain is as follows (the same as modexact), and this is
- what the code runs as.
- ev4 ev5 ev6
- 1 1 1 sub y = x - h
- 23 13 7 mulq q = y * inverse
- 23 15 7 umulh h = high (q * d)
- -- -- --
- 47 30 15
- The time to load src[i+1] and establish x hides under the umulh latency. */
- void
- mpn_divexact_1 (mp_ptr dst, mp_srcptr src, mp_size_t size, mp_limb_t divisor)
- {
- mp_limb_t inverse, lshift_mask, s, sr, s_next, c, h, x, y, q, dummy;
- unsigned rshift, lshift;
- ASSERT (size >= 1);
- ASSERT (divisor != 0);
- ASSERT (MPN_SAME_OR_SEPARATE_P (dst, src, size));
- ASSERT_MPN (src, size);
- ASSERT_LIMB (divisor);
- s_next = *src++; /* src[0] */
- rshift = 0;
- lshift_mask = 0;
- if ((divisor & 1) == 0)
- {
- count_trailing_zeros (rshift, divisor);
- lshift_mask = MP_LIMB_T_MAX;
- divisor >>= rshift;
- }
- binvert_limb (inverse, divisor);
- lshift = 64 - rshift;
- c = 0;
- h = 0;
- sr = s_next >> rshift;
- size--;
- if (LIKELY (size != 0))
- {
- do
- {
- s_next = *src++; /* src[i+1] */
- s = sr | ((s_next << lshift) & lshift_mask);
- x = s - c;
- c = s < c;
- sr = s_next >> rshift;
- y = x - h;
- c += (x < h);
- q = y * inverse;
- *dst++ = q;
- umul_ppmm (h, dummy, q, divisor);
- size--;
- }
- while (size != 0);
- }
- x = sr - c;
- y = x - h;
- q = y * inverse;
- *dst = q; /* dst[size-1] */
- }