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https://github.com/CloverHackyColor/CloverBootloader.git
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71 lines
2.3 KiB
NASM
71 lines
2.3 KiB
NASM
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;------------------------------------------------------------------------------
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;
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; Copyright (c) 2016, Intel Corporation. All rights reserved.<BR>
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; SPDX-License-Identifier: BSD-2-Clause-Patent
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;
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; Module Name:
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;
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; IsZeroBuffer.nasm
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;
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; Abstract:
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;
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; IsZeroBuffer function
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;
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; Notes:
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;
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;------------------------------------------------------------------------------
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DEFAULT REL
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SECTION .text
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;------------------------------------------------------------------------------
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; BOOLEAN
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; EFIAPI
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; InternalMemIsZeroBuffer (
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; IN CONST VOID *Buffer,
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; IN UINTN Length
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; );
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;------------------------------------------------------------------------------
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global ASM_PFX(InternalMemIsZeroBuffer)
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ASM_PFX(InternalMemIsZeroBuffer):
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push rdi
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mov rdi, rcx ; rdi <- Buffer
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xor rcx, rcx ; rcx <- 0
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sub rcx, rdi
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and rcx, 15 ; rcx + rdi aligns on 16-byte boundary
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jz @Is16BytesZero
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cmp rcx, rdx ; Length already in rdx
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cmova rcx, rdx ; bytes before the 16-byte boundary
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sub rdx, rcx
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xor rax, rax ; rax <- 0, also set ZF
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repe scasb
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jnz @ReturnFalse ; ZF=0 means non-zero element found
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@Is16BytesZero:
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mov rcx, rdx
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and rdx, 15
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shr rcx, 4
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jz @IsBytesZero
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.0:
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pxor xmm0, xmm0 ; xmm0 <- 0
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pcmpeqb xmm0, [rdi] ; check zero for 16 bytes
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pmovmskb eax, xmm0 ; eax <- compare results
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; nasm doesn't support 64-bit destination
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; for pmovmskb
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cmp eax, 0xffff
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jnz @ReturnFalse
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add rdi, 16
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loop .0
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@IsBytesZero:
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mov rcx, rdx
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xor rax, rax ; rax <- 0, also set ZF
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repe scasb
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jnz @ReturnFalse ; ZF=0 means non-zero element found
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pop rdi
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mov rax, 1 ; return TRUE
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ret
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@ReturnFalse:
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pop rdi
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xor rax, rax
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ret ; return FALSE
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