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|
; $Id: ASMBitFirstClear.asm $
;; @file
; IPRT - ASMBitFirstClear().
;
;
; Copyright (C) 2006-2019 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 (32/64:eax, 16:ax+dx) Index of the first zero bit.
; @returns (32/64:eax, 16:ax+dx) -1 if no clear bit was found.
; @param msc:rcx gcc:rdi pvBitmap Pointer to the bitmap.
; @param msc:edx gcc:rsi cBits The number of bits in the bitmap. Multiple of 32.
;
BEGINPROC_EXPORTED ASMBitFirstClear
;
; if (cBits)
; Put cBits in ecx first.
;
%if ARCH_BITS == 64
%ifdef ASM_CALL64_GCC
mov ecx, esi
%else
xchg rcx, rdx ; rdx=pvDst, ecx=cBits
%endif
%elif ARCH_BITS == 32
mov ecx, [esp + 4 + 4]
%elif ARCH_BITS == 16
push bp
mov bp, sp
mov ecx, [bp + 4 + 4]
%endif
or ecx, ecx
jz short .failed
;{
push xDI
; asm {...}
%if ARCH_BITS == 64
%ifdef ASM_CALL64_GCC
; rdi = start of scasd - already done
%else
mov rdi, rdx ; rdi = start of scasd (Note! xchg rdx,rcx above)
%endif
%elif ARCH_BITS == 32
mov edi, [esp + 8]
%elif ARCH_BITS == 16
mov ax, [bp + 4 + 2]
mov di, [bp + 4]
mov es, ax ; es is volatile, no need to save.
%endif
add ecx, 31 ; 32 bit aligned
shr ecx, 5 ; number of dwords to scan.
mov xDX, xDI ; xDX = saved pvBitmap
mov eax, 0ffffffffh
repe scasd ; Scan for the first dword with any clear bit.
je .failed_restore
; find the bit in question
sub xDI, 4 ; one step back.
%if ARCH_BITS == 16
movzx edi, di
xor eax, [es:xDI] ; eax = NOT [rdi]
%else
xor eax, [xDI] ; eax = NOT [rdi]
%endif
sub xDI, xDX
shl edi, 3 ; calc bit offset.
bsf ecx, eax
jz .failed_restore ; race paranoia
add ecx, edi
mov eax, ecx
; return success
pop xDI
%if ARCH_BITS == 16
mov edx, eax
shr edx, 16
leave
%endif
ret
; failure
;}
;return -1;
.failed_restore:
pop xDI
.failed:
%if ARCH_BITS != 16
mov eax, 0ffffffffh
%else
mov ax, 0ffffh
mov dx, ax
leave
%endif
ret
ENDPROC ASMBitFirstClear
|
