;------------------------------------------------------------------------------ | |
; | |
; Copyright (c) 2016, Intel Corporation. All rights reserved.<BR> | |
; This program and the accompanying materials | |
; are licensed and made available under the terms and conditions of the BSD License | |
; which accompanies this distribution. The full text of the license may be found at | |
; http://opensource.org/licenses/bsd-license.php. | |
; | |
; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, | |
; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. | |
; | |
; Module Name: | |
; | |
; IsZeroBuffer.nasm | |
; | |
; Abstract: | |
; | |
; IsZeroBuffer function | |
; | |
; Notes: | |
; | |
;------------------------------------------------------------------------------ | |
DEFAULT REL | |
SECTION .text | |
;------------------------------------------------------------------------------ | |
; BOOLEAN | |
; EFIAPI | |
; InternalMemIsZeroBuffer ( | |
; IN CONST VOID *Buffer, | |
; IN UINTN Length | |
; ); | |
;------------------------------------------------------------------------------ | |
global ASM_PFX(InternalMemIsZeroBuffer) | |
ASM_PFX(InternalMemIsZeroBuffer): | |
push rdi | |
mov rdi, rcx ; rdi <- Buffer | |
xor rcx, rcx ; rcx <- 0 | |
sub rcx, rdi | |
and rcx, 15 ; rcx + rdi aligns on 16-byte boundary | |
jz @Is16BytesZero | |
cmp rcx, rdx ; Length already in rdx | |
cmova rcx, rdx ; bytes before the 16-byte boundary | |
sub rdx, rcx | |
xor rax, rax ; rax <- 0, also set ZF | |
repe scasb | |
jnz @ReturnFalse ; ZF=0 means non-zero element found | |
@Is16BytesZero: | |
mov rcx, rdx | |
and rdx, 15 | |
shr rcx, 4 | |
jz @IsBytesZero | |
.0: | |
pxor xmm0, xmm0 ; xmm0 <- 0 | |
pcmpeqb xmm0, [rdi] ; check zero for 16 bytes | |
pmovmskb eax, xmm0 ; eax <- compare results | |
; nasm doesn't support 64-bit destination | |
; for pmovmskb | |
cmp eax, 0xffff | |
jnz @ReturnFalse | |
add rdi, 16 | |
loop .0 | |
@IsBytesZero: | |
mov rcx, rdx | |
xor rax, rax ; rax <- 0, also set ZF | |
repe scasb | |
jnz @ReturnFalse ; ZF=0 means non-zero element found | |
pop rdi | |
mov rax, 1 ; return TRUE | |
ret | |
@ReturnFalse: | |
pop rdi | |
xor rax, rax | |
ret ; return FALSE | |