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Diffstat (limited to '')
| -rw-r--r-- | src/VBox/Runtime/common/asm/ASMBitNextClear.asm | 173 |
1 files changed, 173 insertions, 0 deletions
diff --git a/src/VBox/Runtime/common/asm/ASMBitNextClear.asm b/src/VBox/Runtime/common/asm/ASMBitNextClear.asm new file mode 100644 index 00000000..aad24260 --- /dev/null +++ b/src/VBox/Runtime/common/asm/ASMBitNextClear.asm @@ -0,0 +1,173 @@ +; $Id: ASMBitNextClear.asm $ +;; @file +; IPRT - ASMBitNextClear(). +; + +; +; 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 next 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. +; @param msc:r8d gcc:rcx iBitPrev The previous bit, start searching after it. +; +; @remarks Not quite sure how much sense it makes to do this in assembly, but +; it started out with the ASMBit* API, so that's why we still have it. +; +BEGINPROC_EXPORTED ASMBitNextClear +%if ARCH_BITS == 16 + push bp + mov bp, sp +%endif + push xDI + + ; + ; Align input registers: rdi=pvBitmap, ecx=iPrevBit + ; +%if ARCH_BITS == 64 + %ifdef ASM_CALL64_GCC + ; ecx = iBitPrev param, rdi=pvBitmap param. + %else + mov rdi, rcx ; rdi=pvBits + mov ecx, r8d ; ecx=iPrevBit + mov r8d, edx ; r8d=cBits (saved for .scan_dwords) + %endif + mov r9, rdi ; Save rdi for bit calculation. +%elif ARCH_BITS == 32 + mov edi, [esp + 8] ; edi=pvBits + mov ecx, [esp + 8 + 8] ; ecx=iPrevBit +%elif ARCH_BITS == 16 + les di, [bp + 4] ; es:di=pvBits + mov ecx, [bp + 4 + 8] ; ecx=iPrevBit +%endif + + ; + ; If iPrevBit and iPrevBit + 1 are in the same dword, inspect it for further bits. + ; + inc ecx + mov eax, ecx + shr eax, 5 + shl eax, 2 ; eax=byte offset into bitmap of current dword. + add xDI, xAX ; xDI=current dword address (of iPrevBit + 1). + and ecx, 31 + jz .scan_dwords + +%if ARCH_BITS == 16 + mov edx, [es:di] +%else + mov edx, [xDI] +%endif + not edx ; edx = inverted current dword + shr edx, cl ; Shift out bits that we have searched. + jz .next_dword ; If zero, nothing to find. Go rep scasd. + shl edx, cl ; Shift it back so bsf will return the right index. + + bsf edx, edx ; edx=index of first clear bit + + shl eax, 3 ; Turn eax back into a bit offset of the current dword. + add eax, edx ; eax=bit offset + +.return: + pop xDI +%if ARCH_BITS == 16 + mov edx, eax + shr edx, 16 + leave +%endif + ret + + ; + ; Do dword scan. + ; + + ; Skip empty dword. +.next_dword: + add xDI, 4 ; Skip the empty dword. + add eax, 4 + +.scan_dwords: + ; First load and align bit count. +%if ARCH_BITS == 64 + %ifdef ASM_CALL64_GCC + mov ecx, esi + %else + mov ecx, r8d + %endif +%elif ARCH_BITS == 32 + mov ecx, [esp + 8 + 4] +%elif ARCH_BITS == 16 + mov ecx, [bp + 4 + 4] +%endif + add ecx, 31 + shr ecx, 5 ; ecx=bitmap size in dwords. + + ; Adjust ecx to how many dwords there are left to scan. (eax = current byte offset) + shr eax, 2 ; eax=current dword offset. + sub ecx, eax + jbe .return_failure + + ; Do the scanning. + cld + mov eax, 0ffffffffh + repe scasd + je .return_failure + + ; Find the bit in question. + sub xDI, 4 ; One step back. +%if ARCH_BITS == 16 + movzx edi, di + xor eax, [es:xDI] +%else + xor eax, [xDI] +%endif + bsf eax, eax + jz .return_failure ; race paranoia + + ; Calc the bit offset. +%if ARCH_BITS == 16 + sub di, [bp + 4] + movzx edi, di +%elif ARCH_BITS == 32 + sub xDI, [esp + 8] +%elif ARCH_BITS == 64 + sub xDI, r9 +%endif + shl edi, 3 ; edi=bit offset of current dword. + add eax, edi + jmp .return + +.return_failure: + mov eax, 0ffffffffh + jmp .return +ENDPROC ASMBitNextClear + |