88 lines
2.6 KiB
ArmAsm
88 lines
2.6 KiB
ArmAsm
/* Copy SRC to DEST returning the address of the terminating '\0' in DEST.
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For Intel 80x86, x>=3.
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Copyright (C) 1994-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* This function is defined neither in ANSI nor POSIX standards but is
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also not invented here. */
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#include <sysdep.h>
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#include "asm-syntax.h"
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#define PARMS 4 /* no space for saved regs */
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#define RTN PARMS
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#define DEST RTN
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#define SRC DEST+4
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.text
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ENTRY (__stpcpy)
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movl DEST(%esp), %eax
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movl SRC(%esp), %ecx
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subl %eax, %ecx /* magic: reduce number of loop variants
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to one using addressing mode */
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/* Here we would like to write
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subl $4, %eax
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ALIGN (4)
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but the assembler is too smart and optimizes for the shortest
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form where the number only needs one byte. But if we could
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have the long form we would not need the alignment. */
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.byte 0x81, 0xe8 /* This is `subl $0x00000004, %eax' */
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.long 0x00000004
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/* Four times unfolded loop with only one loop counter. This
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is achieved by the use of index+base addressing mode. As the
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loop counter we use the destination address because this is
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also the result. */
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L(1): addl $4, %eax /* increment loop counter */
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movb (%eax,%ecx), %dl /* load current char */
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movb %dl, (%eax) /* and store it */
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testb %dl, %dl /* was it NUL? */
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jz L(2) /* yes, then exit */
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movb 1(%eax,%ecx), %dl /* load current char */
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movb %dl, 1(%eax) /* and store it */
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testb %dl, %dl /* was it NUL? */
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jz L(3) /* yes, then exit */
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movb 2(%eax,%ecx), %dl /* load current char */
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movb %dl, 2(%eax) /* and store it */
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testb %dl, %dl /* was it NUL? */
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jz L(4) /* yes, then exit */
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movb 3(%eax,%ecx), %dl /* load current char */
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movb %dl, 3(%eax) /* and store it */
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testb %dl, %dl /* was it NUL? */
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jnz L(1) /* no, then continue loop */
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incl %eax /* correct loop counter */
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L(4): incl %eax
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L(3): incl %eax
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L(2):
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ret
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END (__stpcpy)
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weak_alias (__stpcpy, stpcpy)
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libc_hidden_def (__stpcpy)
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libc_hidden_builtin_def (stpcpy)
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