source: vbox/trunk/src/VBox/Runtime/common/string/memcmp.asm

; $Id: memcmp.asm 98103 2023-01-17 14:15:46Z vboxsync $
;; @file
; IPRT - No-CRT memcmp - AMD64 & X86.
;

;
; Copyright (C) 2006-2023 Oracle and/or its affiliates.
;
; This file is part of VirtualBox base platform packages, as
; available from https://www.virtualbox.org.
;
; This program is free software; you can redistribute it and/or
; modify it under the terms of the GNU General Public License
; as published by the Free Software Foundation, in version 3 of the
; License.
;
; This program is distributed in the hope that it will be useful, but
; WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
; General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program; if not, see <https://www.gnu.org/licenses>.
;
; The contents of this file may alternatively be used under the terms
; of the Common Development and Distribution License Version 1.0
; (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
; in the VirtualBox 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.
;
; SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
;

%include "iprt/asmdefs.mac"

BEGINCODE

;;
; @param    pv1     gcc: rdi  msc: rcx  x86:[esp+4]   wcall: eax
; @param    pv2     gcc: rsi  msc: rdx  x86:[esp+8]   wcall: edx
; @param    cb      gcc: rdx  msc: r8   x86:[esp+0ch] wcall: ebx
RT_NOCRT_BEGINPROC memcmp
        cld

        ; Do the bulk of the work.
%ifdef RT_ARCH_AMD64
 %ifdef ASM_CALL64_MSC
        mov     r10, rdi                ; save
        mov     r11, rsi                ; save
        mov     rdi, rcx
        mov     rsi, rdx
        mov     rcx, r8
        mov     rdx, r8
 %else
        mov     rcx, rdx
 %endif
        shr     rcx, 3
        xor     eax, eax
        repe cmpsq
        jne     .not_equal_qword
%else
        push    edi
        push    esi

 %ifdef ASM_CALL32_WATCOM
        mov     edi, eax
        mov     esi, edx
        mov     ecx, ebx
        mov     edx, ebx
 %else
        mov     ecx, [esp + 0ch + 8]
        mov     edi, [esp + 04h + 8]
        mov     esi, [esp + 08h + 8]
        mov     edx, ecx
 %endif
        jecxz   .done
        shr     ecx, 2
        xor     eax, eax
        repe cmpsd
        jne     .not_equal_dword
%endif

        ; The remaining bytes.
%ifdef RT_ARCH_AMD64
        test    dl, 4
        jz      .dont_cmp_dword
        cmpsd
        jne     .not_equal_dword
%endif
.dont_cmp_dword:
        test    dl, 2
        jz      .dont_cmp_word
        cmpsw
        jne     .not_equal_word
.dont_cmp_word:
        test    dl, 1
        jz      .dont_cmp_byte
        cmpsb
        jne     .not_equal_byte
.dont_cmp_byte:

.done:
%ifdef RT_ARCH_AMD64
 %ifdef ASM_CALL64_MSC
        mov     rdi, r10
        mov     rsi, r11
 %endif
%else
        pop     esi
        pop     edi
%endif
        ret

;
; Mismatches.
;
%ifdef RT_ARCH_AMD64
.not_equal_qword:
        mov     ecx, 8
        sub     rsi, 8
        sub     rdi, 8
        repe cmpsb
.not_equal_byte:
        mov     al, [xDI-1]
        movzx   ecx, byte [xSI-1]
        sub     eax, ecx
        jmp     .done
%endif

.not_equal_dword:
        mov     ecx, 4
        sub     xSI, 4
        sub     xDI, 4
        repe cmpsb
%ifdef RT_ARCH_AMD64
        jmp     .not_equal_byte
%else
.not_equal_byte:
        mov     al, [xDI-1]
        movzx   ecx, byte [xSI-1]
        sub     eax, ecx
        jmp     .done
%endif

.not_equal_word:
        mov     ecx, 2
        sub     xSI, 2
        sub     xDI, 2
        repe cmpsb
        jmp     .not_equal_byte
ENDPROC RT_NOCRT(memcmp)