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;; @file
; IPRT - ASMBitFirstSet().
;
;
; Copyright (C) 2006-2010 Oracle Corporation
;
; This file is part of VirtualBox Open Source Edition (OSE), as
; available from http://www.virtualbox.org. This file is free software;
; you can redistribute it and/or modify it under the terms of the GNU
; General Public License (GPL) as published by the Free Software
; Foundation, in version 2 as it comes in the "COPYING" file of the
; VirtualBox OSE distribution. VirtualBox OSE is distributed in the
; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
;
; The contents of this file may alternatively be used under the terms
; of the Common Development and Distribution License Version 1.0
; (CDDL) only, as it comes in the "COPYING.CDDL" file of the
; VirtualBox OSE distribution, in which case the provisions of the
; CDDL are applicable instead of those of the GPL.
;
; You may elect to license modified versions of this file under the
; terms and conditions of either the GPL or the CDDL or both.
;
;*******************************************************************************
;* Header Files *
;*******************************************************************************
%include "iprt/asmdefs.mac"
BEGINCODE
;;
; Finds the first set bit in a bitmap.
;
; @returns eax Index of the first set bit.
; @returns eax -1 if no clear bit was found.
; @param rcx pvBitmap Pointer to the bitmap.
; @param edx cBits The number of bits in the bitmap. Multiple of 32.
;
BEGINPROC_EXPORTED ASMBitFirstSet
;if (cBits)
or edx, edx
jz short .failed
;{
push rdi
; asm {...}
mov rdi, rcx ; rdi = start of scasd
mov ecx, edx
add ecx, 31 ; 32 bit aligned
shr ecx, 5 ; number of dwords to scan.
mov rdx, rdi ; rdx = saved pvBitmap
xor eax, eax
repe scasd ; Scan for the first dword with any set bit.
je .failed_restore
; find the bit in question
lea rdi, [rdi - 4] ; one step back.
mov eax, [rdi]
sub rdi, rdx
shl edi, 3 ; calc bit offset.
mov ecx, 0ffffffffh
bsf ecx, eax
add ecx, edi
mov eax, ecx
; return success
pop rdi
ret
; failure
;}
;return -1;
.failed_restore:
pop rdi
.failed:
mov eax, 0ffffffffh
ret
ENDPROC ASMBitFirstSet
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