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; $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
|
