Index: /trunk/src/VBox/Runtime/common/asm/ASMBitFirstClear.asm
===================================================================
--- /trunk/src/VBox/Runtime/common/asm/ASMBitFirstClear.asm	(revision 58752)
+++ /trunk/src/VBox/Runtime/common/asm/ASMBitFirstClear.asm	(revision 58753)
@@ -93,10 +93,9 @@
         xor     eax, [edi]              ; eax = NOT [rdi]
 %endif
-        jz      .failed_restore         ; race paranoia
         sub     xDI, xDX
         shl     edi, 3                  ; calc bit offset.
 
-        mov     ecx, 0ffffffffh
         bsf     ecx, eax
+        jz      .failed_restore         ; race paranoia
         add     ecx, edi
         mov     eax, ecx
@@ -105,4 +104,6 @@
         pop     xDI
 %if ARCH_BITS == 16
+        mov     edx, eax
+        shr     edx, 16
         leave
 %endif
@@ -114,11 +115,4 @@
 .failed_restore:
         pop     xDI
-%if ARCH_BITS == 16
-        mov     edx, eax
-        shr     edx, 16
-        leave
-%endif
-        ret
-
 .failed:
 %if ARCH_BITS != 16
Index: /trunk/src/VBox/Runtime/common/asm/ASMBitFirstSet.asm
===================================================================
--- /trunk/src/VBox/Runtime/common/asm/ASMBitFirstSet.asm	(revision 58753)
+++ /trunk/src/VBox/Runtime/common/asm/ASMBitFirstSet.asm	(revision 58753)
@@ -0,0 +1,127 @@
+; $Id: $
+;; @file
+; IPRT - ASMBitFirstClear().
+;
+
+;
+; Copyright (C) 2006-2015 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 (32/64:eax, 16:ax+dx)   Index of the first zero bit.
+; @returns (32/64:eax, 16:ax+dx)  -1 if no set 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 ASMBitFirstSet
+        ;
+        ; if (cBits)
+        ; Put cBits in ecx first.
+        ;
+%if    ARCH_BITS == 64
+ %ifdef ASM_CALL64_GCC
+        mov     ecx, esi
+ %else
+        xchg    ecx, edx                ; 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 + 4]
+%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
+        xor     eax, eax
+        repe scasd                      ; Scan for the first dword with any bit set.
+        je      .failed_restore
+
+        ; find the bit in question
+        sub     xDI, 4                  ; one step back.
+%if ARCH_BITS == 16
+        movzx   edi, di
+        mov     eax, [es:xDI]           ; eax = NOT [rdi]
+%else
+        mov     eax, [edi]              ; 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 ASMBitFirstSet
+