VirtualBox

source: vbox/trunk/src/VBox/Runtime/common/asm/ASMBitLastSetU16.asm@ 103795

Last change on this file since 103795 was 98103, checked in by vboxsync, 23 months ago

Copyright year updates by scm.

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1; $Id: ASMBitLastSetU16.asm 98103 2023-01-17 14:15:46Z vboxsync $
2;; @file
3; IPRT - ASMBitLastSetU16().
4;
5
6;
7; Copyright (C) 2006-2023 Oracle and/or its affiliates.
8;
9; This file is part of VirtualBox base platform packages, as
10; available from https://www.virtualbox.org.
11;
12; This program is free software; you can redistribute it and/or
13; modify it under the terms of the GNU General Public License
14; as published by the Free Software Foundation, in version 3 of the
15; License.
16;
17; This program is distributed in the hope that it will be useful, but
18; WITHOUT ANY WARRANTY; without even the implied warranty of
19; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20; General Public License for more details.
21;
22; You should have received a copy of the GNU General Public License
23; along with this program; if not, see <https://www.gnu.org/licenses>.
24;
25; The contents of this file may alternatively be used under the terms
26; of the Common Development and Distribution License Version 1.0
27; (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
28; in the VirtualBox distribution, in which case the provisions of the
29; CDDL are applicable instead of those of the GPL.
30;
31; You may elect to license modified versions of this file under the
32; terms and conditions of either the GPL or the CDDL or both.
33;
34; SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
35;
36
37
38;*******************************************************************************
39;* Header Files *
40;*******************************************************************************
41%include "iprt/asmdefs.mac"
42
43BEGINCODE
44
45;;
46; Finds the last bit which is set in the given 16-bit integer.
47;
48; Bits are numbered from 1 (least significant) to 16.
49;
50; @returns (xAX) index [1..16] of the last set bit.
51; @returns (xAX) 0 if all bits are cleared.
52; @param msc:cx gcc:di x86:stack u16 Integer to search for set bits.
53;
54; @cproto DECLASM(unsigned) ASMBitLastSetU16(uint32_t u16);
55;
56RT_BEGINPROC ASMBitLastSetU16
57%if ARCH_BITS == 16
58 CPU 8086
59 push bp
60 mov bp, sp
61
62 mov cx, [bp + 2 + 2]
63 test cx, cx ; check if zero (eliminates checking dec ax result)
64 jz .return_zero
65
66 mov ax, 16
67.next_bit:
68 shl cx, 1
69 jc .return
70 dec ax
71 jmp .next_bit
72
73.return_zero:
74 xor ax, ax
75.return:
76 pop bp
77 ret
78
79%else
80 xor eax, eax
81 %if ARCH_BITS == 64
82 %ifdef ASM_CALL64_GCC
83 bsr ax, si
84 %else
85 bsr ax, cx
86 %endif
87 %elif ARCH_BITS == 32
88 bsr ax, word [esp + 4]
89 %else
90 %error "Missing or invalid ARCH_BITS."
91 %endif
92 jz .return_zero
93 inc eax
94.return:
95 ret
96.return_zero:
97 xor eax, eax
98 ret
99%endif
100ENDPROC ASMBitLastSetU16
101
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