; $Id: ASMBitLastSetU64.asm 82968 2020-02-04 10:35:17Z vboxsync $ ;; @file ; IPRT - ASMBitLastSetU64(). ; ; ; Copyright (C) 2006-2020 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 last bit which is set in the given 64-bit integer. ; ; Bits are numbered from 1 (least significant) to 64. ; ; @returns (xAX) index [1..64] of the last set bit. ; @returns (xAX) 0 if all bits are cleared. ; @param msc:rcx gcc:rdi x86:stack u64 Integer to search for set bits. ; ; @cproto DECLASM(unsigned) ASMBitLastSetU64(uint64_t u64); ; BEGINPROC_EXPORTED ASMBitLastSetU64 %if ARCH_BITS == 16 CPU 8086 push bp mov bp, sp ; 63:48 mov ax, 64 mov cx, [bp + 2 + 2 + 6] test cx, cx jnz .next_bit ; 47:32 mov al, 48 or cx, [bp + 2 + 2 + 4] jnz .next_bit ; 31:16 mov al, 32 or cx, [bp + 2 + 2 + 2] jnz .next_bit ; 16:0 mov al, 16 or cx, [bp + 2 + 2 + 0] jz .return_zero ; find the bit that was set. .next_bit: shl cx, 1 jc .return dec ax jmp .next_bit .return_zero: xor ax, ax .return: pop bp ret %else %if ARCH_BITS == 64 %ifdef ASM_CALL64_GCC bsr rax, rsi %else bsr rax, rcx %endif jz .return_zero inc eax .return: ret %elif ARCH_BITS == 32 ; Check the 2nd dword then the first one. bsr eax, dword [esp + 4 + 4] jz .check_1st_dword add eax, 32 ret .check_1st_dword: bsr eax, dword [esp + 4 + 0] jz .return_zero inc eax ret %else %error "Missing or invalid ARCH_BITS." %endif .return_zero: xor eax, eax ret %endif ENDPROC ASMBitLastSetU64