diff options
Diffstat (limited to 'src/VBox/Devices/BiosCommonCode/__U4M.asm')
| -rw-r--r-- | src/VBox/Devices/BiosCommonCode/__U4M.asm | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/src/VBox/Devices/BiosCommonCode/__U4M.asm b/src/VBox/Devices/BiosCommonCode/__U4M.asm new file mode 100644 index 00000000..93781883 --- /dev/null +++ b/src/VBox/Devices/BiosCommonCode/__U4M.asm @@ -0,0 +1,125 @@ +; $Id: __U4M.asm $ +;; @file +; Compiler support routines. +; + +; +; Copyright (C) 2012-2022 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>. +; +; SPDX-License-Identifier: GPL-3.0-only +; + + +;******************************************************************************* +;* Exported Symbols * +;******************************************************************************* +public __U4M + +; MASM (ML.EXE) is used for PXE and no longer understands the .8086 directive. +; WASM is used for the BIOS and understands it just fine. +ifdef __WASM__ + .8086 +endif + +_TEXT segment public 'CODE' use16 + assume cs:_TEXT + +;; +; 32-bit unsigned multiplication. +; +; @param dx:ax Factor 1. +; @param cx:bx Factor 2. +; @returns dx:ax Result. +; +__U4M: + pushf +if VBOX_BIOS_CPU ge 80386 + .386 + push eax + push edx + push ecx + + rol eax, 16 + mov ax, dx + ror eax, 16 + xor edx, edx + + shr ecx, 16 + mov cx, bx + + mul ecx ; eax * ecx -> edx:eax + + pop ecx + + pop edx + ror eax, 16 + mov dx, ax + add sp, 2 + pop ax + rol eax, 16 +ifdef __WASM__ + .8086 +endif + +else + push si ; high result + push di ; low result + + ; + ; dx:ax * cx:bx = + ;----------------------- + ; ax*bx + ; + dx*bx ; only lower 16 bits relevant. + ; + ax*cx ; ditto + ; +dx*cx ; not relevant + ; ------------- + ; = dx:ax + ; + + push ax ; stash the low factor 1 part for the 3rd multiplication. + mov di, dx ; stash the high factor 1 part for the 2nd multiplication. + + ; multiply the two low factor "digits": ax * bx + mul bx + mov si, dx + xchg di, ax ; save low result and loads high factor 1 into ax for the next step + + ; Multiply the low right "digit" by the high left one and add it to the high result part + mul bx + add si, ax + + ; Multiply the high right "digit" by the low left on and add it ot the high result part. + pop ax + mul cx + add si, ax + + ; Load the result. + mov dx, si + mov ax, di + + pop di + pop si +endif + popf + ret + + +_TEXT ends + end + |