; $Id: ASMBitFirstSetU16.asm 59861 2016-02-26 19:56:44Z vboxsync $ ;; @file ; IPRT - ASMBitFirstSetU16(). ; ; ; Copyright (C) 2006-2016 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 bit which is set in the given 16-bit integer. ; ; Bits are numbered from 1 (least significant) to 16. ; ; @returns (xAX) index [1..16] of the first set bit. ; @returns (xAX) 0 if all bits are cleared. ; @param msc:cx gcc:di x86:stack u16 Integer to search for set bits. ; ; @cproto DECLASM(unsigned) ASMBitFirstSetU16(uint16_t u16); ; BEGINPROC_EXPORTED ASMBitFirstSetU16 %if ARCH_BITS == 16 CPU 8086 push bp mov bp, sp ; 16:0 mov ax, 1 mov cx, [bp + 2 + 2 + 0] test cx, cx jz .return_zero ; find the bit that was set. .next_bit: shr cx, 1 jc .return inc ax jmp .next_bit .return_zero: xor ax, ax .return: pop bp ret %else xor eax, eax %if ARCH_BITS == 64 %ifdef ASM_CALL64_GCC bsf ax, si %else bsf ax, cx %endif %elif ARCH_BITS == 32 bsf ax, word [esp + 4] %else %error "Missing or invalid ARCH_BITS." %endif jz .return_zero inc eax .return: ret .return_zero: xor eax, eax ret %endif ENDPROC ASMBitFirstSetU16