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; $Id: bs3-wc32-U8M.asm $
;; @file
; BS3Kit - 32-bit Watcom C/C++, 64-bit integer multiplication.
;
;
; Copyright (C) 2007-2023 Oracle and/or its affiliates.
;
; This file is part of VirtualBox base platform packages, as
; available from https://www.virtualbox.org.
;
; This program is free software; you can redistribute it and/or
; modify it under the terms of the GNU General Public License
; as published by the Free Software Foundation, in version 3 of the
; License.
;
; This program 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
; General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program; if not, see <https://www.gnu.org/licenses>.
;
; The contents of this file may alternatively be used under the terms
; of the Common Development and Distribution License Version 1.0
; (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
; in the VirtualBox distribution, in which case the provisions of the
; CDDL are applicable instead of those of the GPL.
;
; You may elect to license modified versions of this file under the
; terms and conditions of either the GPL or the CDDL or both.
;
; SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
;
%include "bs3kit-template-header.mac"
;;
; 64-bit unsigned & signed integer multiplication.
;
; @returns EDX:EAX as the product.
; @param EDX:EAX Factor 1 - edx=F1H, eax=F1L.
; @param ECX:EBX Factor 2 - ecx=F2H, ebx=F2L.
;
global $??I8M
$??I8M:
global $??U8M
$??U8M:
;
; If both the high dwords are zero, we can get away with
; a simple 32-bit multiplication.
;
test ecx, ecx
jnz .big
test edx, edx
jnz .big
mul ebx
ret
.big:
;
; Imagine we use 4294967296-base (2^32), so each factor has two
; digits H and L, thus we have: F1H:F1L * F2H:F1L which we can
; multipy like we learned in primary school. Since the result
; is limited to 64-bit, we can skip F1H*F2H and discard the
; high 32-bit in F1L*F2H and F1H*F2L.
; result = ((F1L*F2H) << 32)
; + ((F1H*F2L) << 32)
; + (F1L*F2L);
;
push ecx ; Preserve ECX just to be nice.
push eax ; Stash F1L for later.
push edx ; Stash F1H for later.
; ECX = F1L*F2H
mul ecx
mov ecx, eax
; ECX += F1H * F2L
pop eax
mul ebx
add ecx, eax
; EDX:EAX = F1L * F2L
pop eax
mul ebx
add edx, ecx
pop ecx
ret
|
