mpn/power/submul_1.asm

0 dnl  IBM POWER mpn_submul_1 -- Multiply a limb vector with a limb and subtract
2 dnl  the result from a second limb vector.
4 dnl  Copyright 1992, 1994, 1999, 2000, 2001 Free Software Foundation, Inc.
6 dnl  This file is part of the GNU MP Library.
8 dnl  The GNU MP Library is free software; you can redistribute it and/or modify
9 dnl  it under the terms of the GNU Lesser General Public License as published
10 dnl  by the Free Software Foundation; either version 3 of the License, or (at
11 dnl  your option) any later version.
13 dnl  The GNU MP Library is distributed in the hope that it will be useful, but
14 dnl  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 dnl  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
16 dnl  License for more details.
18 dnl  You should have received a copy of the GNU Lesser General Public License
19 dnl  along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.
22 dnl  INPUT PARAMETERS
23 dnl  res_ptr	r3
24 dnl  s1_ptr	r4
25 dnl  size	r5
26 dnl  s2_limb	r6
28 dnl  The POWER architecture has no unsigned 32x32->64 bit multiplication
29 dnl  instruction.  To obtain that operation, we have to use the 32x32->64
30 dnl  signed multiplication instruction, and add the appropriate compensation to
31 dnl  the high limb of the result.  We add the multiplicand if the multiplier
32 dnl  has its most significant bit set, and we add the multiplier if the
33 dnl  multiplicand has its most significant bit set.  We need to preserve the
34 dnl  carry flag between each iteration, so we have to compute the compensation
35 dnl  carefully (the natural, srai+and doesn't work).  Since all POWER can
36 dnl  branch in zero cycles, we use conditional branches for the compensation.