VirtualBox

source: vbox/trunk/src/VBox/Runtime/common/asm/ASMBitLastSetU64.asm@ 96407

Last change on this file since 96407 was 96407, checked in by vboxsync, 2 years ago

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1; $Id: ASMBitLastSetU64.asm 96407 2022-08-22 17:43:14Z vboxsync $
2;; @file
3; IPRT - ASMBitLastSetU64().
4;
5
6;
7; Copyright (C) 2006-2022 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 64-bit integer.
47;
48; Bits are numbered from 1 (least significant) to 64.
49;
50; @returns (xAX) index [1..64] of the last set bit.
51; @returns (xAX) 0 if all bits are cleared.
52; @param msc:rcx gcc:rdi x86:stack u64 Integer to search for set bits.
53;
54; @cproto DECLASM(unsigned) ASMBitLastSetU64(uint64_t u64);
55;
56RT_BEGINPROC ASMBitLastSetU64
57%if ARCH_BITS == 16
58 CPU 8086
59 push bp
60 mov bp, sp
61
62 ; 63:48
63 mov ax, 64
64 mov cx, [bp + 2 + 2 + 6]
65 test cx, cx
66 jnz .next_bit
67
68 ; 47:32
69 mov al, 48
70 or cx, [bp + 2 + 2 + 4]
71 jnz .next_bit
72
73 ; 31:16
74 mov al, 32
75 or cx, [bp + 2 + 2 + 2]
76 jnz .next_bit
77
78 ; 16:0
79 mov al, 16
80 or cx, [bp + 2 + 2 + 0]
81 jz .return_zero
82
83 ; find the bit that was set.
84.next_bit:
85 shl cx, 1
86 jc .return
87 dec ax
88 jmp .next_bit
89
90.return_zero:
91 xor ax, ax
92.return:
93 pop bp
94 ret
95
96%else
97 %if ARCH_BITS == 64
98 %ifdef ASM_CALL64_GCC
99 bsr rax, rsi
100 %else
101 bsr rax, rcx
102 %endif
103 jz .return_zero
104 inc eax
105.return:
106 ret
107
108 %elif ARCH_BITS == 32
109 ; Check the 2nd dword then the first one.
110 bsr eax, dword [esp + 4 + 4]
111 jz .check_1st_dword
112 add eax, 32
113 ret
114
115.check_1st_dword:
116 bsr eax, dword [esp + 4 + 0]
117 jz .return_zero
118 inc eax
119 ret
120
121 %else
122 %error "Missing or invalid ARCH_BITS."
123 %endif
124
125.return_zero:
126 xor eax, eax
127 ret
128%endif
129ENDPROC ASMBitLastSetU64
130
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