1 files changed, 76 insertions, 0 deletions
diff --git a/src/VBox/Devices/BiosCommonCode/ASMBitLastSetU16.asm b/src/VBox/Devices/BiosCommonCode/ASMBitLastSetU16.asm
new file mode 100644
index 00000000..f7a45ac9
--- /dev/null
+++ b/src/VBox/Devices/BiosCommonCode/ASMBitLastSetU16.asm
@@ -0,0 +1,76 @@
+; $Id: ASMBitLastSetU16.asm $
+;; @file
+; BiosCommonCode - ASMBitLastSetU16() - borrowed from IPRT.
+;
+
+;
+; Copyright (C) 2006-2022 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
+;
+
+
+;*******************************************************************************
+;* Header Files                                                                *
+;*******************************************************************************
+public _ASMBitLastSetU16
+
+        .8086
+
+_TEXT   segment public 'CODE' use16
+        assume cs:_TEXT
+
+
+;;
+; Finds the last bit which is set in the given 16-bit integer.
+;
+; Bits are numbered from 1 (least significant) to 16.
+;
+; @returns (ax)     index [1..16] of the last set bit.
+; @returns (ax)     0 if all bits are cleared.
+; @param   u16      Integer to search for set bits.
+;
+; @cproto DECLASM(unsigned) ASMBitLastSetU16(uint32_t u16);
+;
+_ASMBitLastSetU16   proc
+        .8086
+        push    bp
+        mov     bp, sp
+
+        mov     cx, [bp + 2 + 2]
+        test    cx, cx                  ; check if zero (eliminates checking dec ax result)
+        jz      return_zero
+
+        mov     ax, 16
+next_bit:
+        shl     cx, 1
+        jc      return
+        dec     ax
+        jmp     next_bit
+
+return_zero:
+        xor     ax, ax
+return:
+        pop     bp
+        ret
+_ASMBitLastSetU16   endp
+
+_TEXT           ends
+                end
+