2013-08-04 18:17:37 -04:00
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; PROLOGUE(mpn_karasub)
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2012-11-25 17:13:44 -05:00
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; mpn_karasub
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;
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; Copyright 2011 The Code Cavern
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;
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; Copyright 2012 Brian Gladman
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;
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; This file is part of the MPIR Library.
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;
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; The MPIR 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
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; by the Free Software Foundation; either version 2.1 of the License, or (at
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; your option) any later version.
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;
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; The MPIR 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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;
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; You should have received a copy of the GNU Lesser General Public License
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; along with the MPIR Library; see the file COPYING.LIB. If not, write
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; to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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; Boston, MA 02110-1301, USA.
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;
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; void mpn_karasub(mp_ptr, mp_ptr, mp_size_t)
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; rax rdi rsi rdx
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; rax rcx rdx r8
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;
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; Karasuba Multiplication - split x and y into two equal length halves so
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; that x = xh.B + xl and y = yh.B + yl. Then their product is:
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;
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; x.y = xh.yh.B^2 + (xh.yl + xl.yh).B + xl.yl
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; = xh.yh.B^2 + (xh.yh + xl.yl - {xh - xl}.{yh - yl}).B + xl.yl
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;
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; If the length of the elements is m (about n / 2), the output length is 4 * m
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; as illustrated below. The middle two blocks involve three additions and one
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; subtraction:
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;
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; -------------------- rp
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; | |-->
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; | A:xl.yl[lo] | |
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; | | | (xh - xl).(yh - yl)
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; -------------------- | -------------------- tp
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; <-- | |<--< <-- | |
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; | | B:xl.yl[hi] | | | E:[lo] |
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; | | | | | |
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; | -------------------- | --------------------
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; >--> | |--> <-- | |
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; |\___ | C:xh.yh[lo] | ____/ | F:[hi] |
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; | | | | |
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; | -------------------- --------------------
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; <-- | |
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; | D:xh.yh[hi] |
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; | |
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; --------------------
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;
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; To avoid overwriting B before it is used, we need to do two operations
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; in parallel:
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;
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; (1) B = B + C + A - E = (B + C) + A - E
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; (2) C = C + B + D - F = (B + C) + D - F
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;
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; The final carry from (1) has to be propagated into C and D, and the final
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; carry from (2) has to be propagated into D. When the number of input limbs
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; is odd, some extra operations have to be undertaken.
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%include "yasm_mac.inc"
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%define reg_save_list rbx, rbp, rsi, rdi, r12, r13, r14, r15
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%macro add_one 1
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lea %1, [%1 + 1]
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%endmacro
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BITS 64
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TEXT
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; requires n >= 8
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FRAME_PROC mpn_karasub, 2, reg_save_list
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mov rdi, rcx
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mov rsi, rdx
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mov rdx, r8
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mov [rsp], rdx
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mov [rsp+8], rdi
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; rp is rdi, tp is rsi, L is rdi, H is rbp, tp is rsi
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; carries/borrows in rax, rbx
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shr rdx, 1
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lea rcx, [rdx+rdx*1]
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lea rbp, [rdi+rcx*8]
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xor rax, rax
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xor rbx, rbx
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lea rdi, [rdi+rdx*8-24]
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lea rsi, [rsi+rdx*8-24]
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lea rbp, [rbp+rdx*8-24]
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mov ecx, 3
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sub rcx, rdx
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mov edx, 3
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align 16
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.1: bt rbx, 2
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mov r8, [rdi+rdx*8]
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adc r8, [rbp+rcx*8]
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mov r12, r8
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mov r9, [rdi+rdx*8+8]
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adc r9, [rbp+rcx*8+8]
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mov r10, [rdi+rdx*8+16]
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adc r10, [rbp+rcx*8+16]
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mov r11, [rdi+rdx*8+24]
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adc r11, [rbp+rcx*8+24]
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rcl rbx, 1
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bt rax, 1
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mov r15, r11
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adc r8, [rdi+rcx*8]
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mov r13, r9
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adc r9, [rdi+rcx*8+8]
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mov r14, r10
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adc r10, [rdi+rcx*8+16]
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adc r11, [rdi+rcx*8+24]
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rcl rax, 1
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bt rbx, 2
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adc r12, [rbp+rdx*8]
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adc r13, [rbp+rdx*8+8]
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adc r14, [rbp+rdx*8+16]
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adc r15, [rbp+rdx*8+24]
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rcl rbx, 1
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bt rax, 1
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sbb r8, [rsi+rcx*8]
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sbb r9, [rsi+rcx*8+8]
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sbb r10, [rsi+rcx*8+16]
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sbb r11, [rsi+rcx*8+24]
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mov [rdi+rdx*8+16], r10
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mov [rdi+rdx*8+24], r11
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rcl rax, 1
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bt rbx, 2
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mov [rdi+rdx*8], r8
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mov [rdi+rdx*8+8], r9
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sbb r12, [rsi+rdx*8]
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sbb r13, [rsi+rdx*8+8]
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sbb r14, [rsi+rdx*8+16]
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sbb r15, [rsi+rdx*8+24]
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rcl rbx, 1
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add rdx, 4
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mov [rbp+rcx*8], r12
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mov [rbp+rcx*8+8], r13
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mov [rbp+rcx*8+16], r14
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mov [rbp+rcx*8+24], r15
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add rcx, 4
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jnc .1
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cmp rcx, 2
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jg .5
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jz .4
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jp .3
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.2: bt rbx, 2
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mov r8, [rdi+rdx*8]
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adc r8, [rbp]
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mov r12, r8
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mov r9, [rdi+rdx*8+8]
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adc r9, [rbp+8]
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mov r10, [rdi+rdx*8+16]
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adc r10, [rbp+16]
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rcl rbx, 1
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bt rax, 1
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adc r8, [rdi]
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mov r13, r9
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adc r9, [rdi+8]
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mov r14, r10
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adc r10, [rdi+16]
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rcl rax, 1
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bt rbx, 2
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adc r12, [rbp+rdx*8]
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adc r13, [rbp+rdx*8+8]
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adc r14, [rbp+rdx*8+16]
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rcl rbx, 1
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bt rax, 1
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sbb r8, [rsi]
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sbb r9, [rsi+8]
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sbb r10, [rsi+16]
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mov [rdi+rdx*8+16], r10
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rcl rax, 1
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bt rbx, 2
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mov [rdi+rdx*8], r8
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mov [rdi+rdx*8+8], r9
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sbb r12, [rsi+rdx*8]
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sbb r13, [rsi+rdx*8+8]
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sbb r14, [rsi+rdx*8+16]
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rcl rbx, 1
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add rdx, 3
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mov [rbp], r12
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mov [rbp+8], r13
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mov [rbp+16], r14
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jmp .5
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.3: bt rbx, 2
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mov r8, [rdi+rdx*8]
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adc r8, [rbp+8]
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mov r12, r8
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mov r9, [rdi+rdx*8+8]
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adc r9, [rbp+16]
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rcl rbx, 1
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bt rax, 1
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adc r8, [rdi+8]
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mov r13, r9
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adc r9, [rdi+16]
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rcl rax, 1
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bt rbx, 2
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adc r12, [rbp+rdx*8]
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adc r13, [rbp+rdx*8+8]
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rcl rbx, 1
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bt rax, 1
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sbb r8, [rsi+8]
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sbb r9, [rsi+16]
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rcl rax, 1
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bt rbx, 2
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mov [rdi+rdx*8], r8
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mov [rdi+rdx*8+8], r9
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sbb r12, [rsi+rdx*8]
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sbb r13, [rsi+rdx*8+8]
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rcl rbx, 1
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add rdx, 2
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mov [rbp+8], r12
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mov [rbp+16], r13
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jmp .5
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.4: bt rbx, 2
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mov r8, [rdi+rdx*8]
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adc r8, [rbp+16]
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mov r12, r8
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rcl rbx, 1
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bt rax, 1
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adc r8, [rdi+16]
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rcl rax, 1
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bt rbx, 2
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adc r12, [rbp+rdx*8]
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rcl rbx, 1
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bt rax, 1
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sbb r8, [rsi+16]
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rcl rax, 1
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bt rbx, 2
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mov [rdi+rdx*8], r8
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sbb r12, [rsi+rdx*8]
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rcl rbx, 1
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add_one rdx
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mov [rbp+rcx*8], r12
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; move low half rbx carry into rax
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.5: rcr rax, 3
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bt rbx, 2
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rcl rax, 3
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mov r8, [rsp]
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mov rcx, rsi
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mov rsi,[rsp+8]
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lea r9, [r8+r8]
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lea rsi, [rsi+r9*8]
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lea r11, [rbp+24]
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sub r11, rsi
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sar r11, 3
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bt r8, 0
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jnc .9
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; if odd the do next two
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add r11, 2
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mov r8, [rbp+rdx*8]
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mov r9, [rbp+rdx*8+8]
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rcr rbx, 2
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adc r8,0
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adc r9, 0
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rcl rbx, 1
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sbb r8, [rcx+rdx*8]
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sbb r9, [rcx+rdx*8+8]
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rcr rbx, 2
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adc [rbp+24], r8
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adc [rbp+32], r9
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rcl rbx, 3
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; Now add in any accummulated carries and/or borrows
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;
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; NOTE: We can't propagate individual borrows or carries from the second
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; and third quarter blocks into the fourth quater block by simply waiting
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; for carry (or borrow) propagation to end. This is because a carry into
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; the fourth quarter block when it contains only maximum integers or a
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; borrow when it contains all zero integers will incorrectly propagate
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; beyond the end of the top quarter block.
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.9: lea rdx, [rdi+rdx*8]
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sub rdx, rsi
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sar rdx, 3
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; carries/borrrow from second to third quarter quarter block
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; rax{2} is the carry in (B + C)
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; rax{1} is the carry in (B + C) + A
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; rax{0} is the borrow in (B + C + A) - E
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mov rcx, rdx
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bt rax, 0
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.10: sbb qword[rsi+rcx*8], 0
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add_one rcx
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jrcxz .11
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jc .10
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.11 mov rcx, rdx
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bt rax, 1
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.12: adc qword[rsi+rcx*8], 0
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add_one rcx
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jrcxz .13
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jc .12
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.13 mov rcx, rdx
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bt rax, 2
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.14: adc qword[rsi+rcx*8], 0
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add_one rcx
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jrcxz .15
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jc .14
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; carries/borrrow from third to fourth quarter quarter block
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; rbx{2} is the carry in (B + C)
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; rbx{1} is the carry in (B + C) + D
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; rbx{0} is the borrow in (B + C + D) - F
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.15: mov rcx, r11
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bt rbx, 0
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.16: sbb qword[rsi+rcx*8], 0
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add_one rcx
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jrcxz .17
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jc .16
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.17: mov rcx, r11
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bt rbx, 1
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.18: adc qword[rsi+rcx*8], 0
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add_one rcx
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jrcxz .19
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jc .18
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.19: mov rcx, r11
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bt rbx, 2
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.20: adc qword[rsi+rcx*8], 0
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add_one rcx
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jrcxz .21
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jc .20
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.21:
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END_PROC reg_save_list
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end
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