MdePkg/Library/BaseMemoryLibOptDxe/X64/IsZeroBuffer.nasm

   1 ;------------------------------------------------------------------------------
   2 ;
   3 ; Copyright (c) 2016, Intel Corporation. All rights reserved.<BR>
   4 ; SPDX-License-Identifier: BSD-2-Clause-Patent
   5 ;
   6 ; Module Name:
   7 ;
   8 ;   IsZeroBuffer.nasm
   9 ;
  10 ; Abstract:
  11 ;
  12 ;   IsZeroBuffer function
  13 ;
  14 ; Notes:
  15 ;
  16 ;------------------------------------------------------------------------------
  17
  18     DEFAULT REL
  19     SECTION .text
  20
  21 ;------------------------------------------------------------------------------
  22 ;  BOOLEAN
  23 ;  EFIAPI
  24 ;  InternalMemIsZeroBuffer (
  25 ;    IN CONST VOID  *Buffer,
  26 ;    IN UINTN       Length
  27 ;    );
  28 ;------------------------------------------------------------------------------
  29 global ASM_PFX(InternalMemIsZeroBuffer)
  30 ASM_PFX(InternalMemIsZeroBuffer):
  31     push    rdi
  32     mov     rdi, rcx                   ; rdi <- Buffer
  33     mov     rcx, rdx                   ; rcx <- Length
  34     shr     rcx, 3                     ; rcx <- number of qwords
  35     and     rdx, 7                     ; rdx <- number of trailing bytes
  36     xor     rax, rax                   ; rax <- 0, also set ZF
  37     repe    scasq
  38     jnz     @ReturnFalse               ; ZF=0 means non-zero element found
  39     mov     rcx, rdx
  40     repe    scasb
  41     jnz     @ReturnFalse
  42     pop     rdi
  43     mov     rax, 1                     ; return TRUE
  44     ret
  45 @ReturnFalse:
  46     pop     rdi
  47     xor     rax, rax
  48     ret                                ; return FALSE
  49