1 /* Cray PVP mpn_sub_n -- subtract two limb vectors and store their difference 2 in a third limb vector. 3 4 Copyright 1996, 2000, 2001 Free Software Foundation, Inc. 5 6 This file is part of the GNU MP Library. 7 8 The GNU MP Library is free software; you can redistribute it and/or modify 9 it under the terms of the GNU Lesser General Public License as published by 10 the Free Software Foundation; either version 3 of the License, or (at your 11 option) any later version. 12 13 The GNU MP Library is distributed in the hope that it will be useful, but 14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16 License for more details. 17 18 You should have received a copy of the GNU Lesser General Public License 19 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 20 21 /* This code runs at 4 cycles/limb. It may be possible to bring it down 22 to 3 cycles/limb. */ 23 24 #include "gmp.h" 25 #include "gmp-impl.h" 26 27 mp_limb_t 28 mpn_sub_n (mp_ptr rp, mp_srcptr up, mp_srcptr vp, mp_size_t n) 29 { 30 mp_limb_t cy[n]; 31 mp_limb_t a, b, r, s0, c0, c1; 32 mp_size_t i; 33 int more_carries; 34 35 /* Main subtract loop. Generate a raw output difference in rp[] and a 36 borrow vector in cy[]. */ 37 #pragma _CRI ivdep 38 for (i = 0; i < n; i++) 39 { 40 a = up[i]; 41 b = vp[i]; 42 s0 = a - b; /* a = s0 + b */ 43 rp[i] = s0; 44 c0 = ((s0 & b) | ((s0 | b) & ~a)) >> 63; 45 cy[i] = c0; 46 } 47 /* Borrow subtract loop. Subtract the borrow vector cy[] from the raw 48 difference rp[] and store the new difference back to rp[0]. If this 49 generates further borrow, set more_carries. */ 50 more_carries = 0; 51 #pragma _CRI ivdep 52 for (i = 1; i < n; i++) 53 { 54 r = rp[i]; 55 c0 = cy[i - 1]; 56 s0 = r - c0; /* r = s0 + c0 */ 57 rp[i] = s0; 58 c0 = (s0 & ~r) >> 63; 59 more_carries += c0; 60 } 61 /* If that second loop generated borrow, handle that in scalar loop. */ 62 if (more_carries) 63 { 64 mp_limb_t cyrec = 0; 65 /* Look for places where rp[k] contains just ones and cy[k-1] is 66 non-zero. These are where we got a recurrency borrow. */ 67 for (i = 1; i < n; i++) 68 { 69 r = rp[i]; 70 c0 = (~r == 0 && cy[i - 1] != 0); 71 s0 = r - cyrec; 72 rp[i] = s0; 73 c1 = (s0 & ~r) >> 63; 74 cyrec = c0 | c1; 75 } 76 return cyrec | cy[n - 1]; 77 } 78 79 return cy[n - 1]; 80 } 81