;; @file

; IPRT - ASMBitFirstClear().

;

;

; Copyright (C) 2006-2007 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 clear bit in a bitmap.

;

; @returns eax Index of the first zero 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 ASMBitFirstClear

;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

mov eax, 0ffffffffh

repe scasd ; Scan for the first dword with any clear bit.

je .failed_restore

; find the bit in question

lea rdi, [rdi - 4] ; one step back.

xor eax, [rdi] ; eax = NOT [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

ret

.failed:

mov eax, 0ffffffffh

ret

ENDPROC ASMBitFirstClear