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Diffstat (limited to 'src/VBox/ValidationKit/bootsectors/bs3kit/bs3-wc32-U8M.asm')
| -rw-r--r-- | src/VBox/ValidationKit/bootsectors/bs3kit/bs3-wc32-U8M.asm | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-wc32-U8M.asm b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-wc32-U8M.asm new file mode 100644 index 00000000..57a1e583 --- /dev/null +++ b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-wc32-U8M.asm @@ -0,0 +1,93 @@ +; $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 + |