1 /* Alpha mpn_divexact_1 -- mpn by limb exact division. 2 3 THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY. THEY'RE ALMOST 4 CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN 5 FUTURE GNU MP RELEASES. 6 7 Copyright 2000, 2001, 2002, 2003 Free Software Foundation, Inc. 8 9 This file is part of the GNU MP Library. 10 11 The GNU MP Library is free software; you can redistribute it and/or modify 12 it under the terms of the GNU Lesser General Public License as published by 13 the Free Software Foundation; either version 3 of the License, or (at your 14 option) any later version. 15 16 The GNU MP Library is distributed in the hope that it will be useful, but 17 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 18 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 19 License for more details. 20 21 You should have received a copy of the GNU Lesser General Public License 22 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 23 24 #include "gmp.h" 25 #include "gmp-impl.h" 26 #include "longlong.h" 27 28 29 /* cycles/limb 30 EV4: 47.0 31 EV5: 30.0 32 EV6: 15.0 33 */ 34 35 36 /* The dependent chain is as follows (the same as modexact), and this is 37 what the code runs as. 38 39 ev4 ev5 ev6 40 1 1 1 sub y = x - h 41 23 13 7 mulq q = y * inverse 42 23 15 7 umulh h = high (q * d) 43 -- -- -- 44 47 30 15 45 46 The time to load src[i+1] and establish x hides under the umulh latency. */ 47 48 void 49 mpn_divexact_1 (mp_ptr dst, mp_srcptr src, mp_size_t size, mp_limb_t divisor) 50 { 51 mp_limb_t inverse, lshift_mask, s, sr, s_next, c, h, x, y, q, dummy; 52 unsigned rshift, lshift; 53 54 ASSERT (size >= 1); 55 ASSERT (divisor != 0); 56 ASSERT (MPN_SAME_OR_SEPARATE_P (dst, src, size)); 57 ASSERT_MPN (src, size); 58 ASSERT_LIMB (divisor); 59 60 s_next = *src++; /* src[0] */ 61 62 rshift = 0; 63 lshift_mask = 0; 64 if ((divisor & 1) == 0) 65 { 66 count_trailing_zeros (rshift, divisor); 67 lshift_mask = MP_LIMB_T_MAX; 68 divisor >>= rshift; 69 } 70 71 binvert_limb (inverse, divisor); 72 lshift = 64 - rshift; 73 74 c = 0; 75 h = 0; 76 sr = s_next >> rshift; 77 78 size--; 79 if (LIKELY (size != 0)) 80 { 81 do 82 { 83 s_next = *src++; /* src[i+1] */ 84 s = sr | ((s_next << lshift) & lshift_mask); 85 x = s - c; 86 c = s < c; 87 sr = s_next >> rshift; 88 89 y = x - h; 90 c += (x < h); 91 q = y * inverse; 92 *dst++ = q; 93 umul_ppmm (h, dummy, q, divisor); 94 95 size--; 96 } 97 while (size != 0); 98 } 99 100 x = sr - c; 101 y = x - h; 102 q = y * inverse; 103 *dst = q; /* dst[size-1] */ 104 } 105