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148 lines
4.6 KiB
ArmAsm
148 lines
4.6 KiB
ArmAsm
/* copy no more than N bytes from SRC to DEST, returning the address of
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the terminating '\0' in DEST.
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For Intel 80x86, x>=3.
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Copyright (C) 1994-2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>
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Some bug fixes by Alan Modra <Alan@SPRI.Levels.UniSA.Edu.Au>
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- original wrote n+1 chars in some cases.
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- stpncpy() ought to behave like strncpy() ie. not null-terminate
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if limited by n. glibc-1.09 stpncpy() does this.
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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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<http://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include "asm-syntax.h"
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#define PARMS 4+4 /* space for 1 saved reg */
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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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#define LEN SRC+4
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.text
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ENTRY (__stpncpy)
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pushl %esi
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cfi_adjust_cfa_offset (4)
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movl DEST(%esp), %eax
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movl SRC(%esp), %esi
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cfi_rel_offset (esi, 0)
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movl LEN(%esp), %ecx
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subl %eax, %esi /* magic: reduce number of loop variants
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to one using addressing mode */
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jmp L(1) /* jump to loop "head" */
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ALIGN(4)
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/* Four times unfolded loop with two loop counters. We get the
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third value (the source address) by using the index+base
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addressing mode. */
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L(2): movb (%eax,%esi), %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(7) /* yes, then exit */
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movb 1(%eax,%esi), %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(6) /* yes, then exit */
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movb 2(%eax,%esi), %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(5) /* yes, then exit */
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movb 3(%eax,%esi), %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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jz L(4) /* yes, then exit */
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addl $4, %eax /* increment loop counter for full round */
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L(1): subl $4, %ecx /* still more than 4 bytes allowed? */
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jae L(2) /* yes, then go to start of loop */
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/* The maximal remaining 15 bytes are not processed in a loop. */
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addl $4, %ecx /* correct above subtraction */
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jz L(9) /* maximal allowed char reached => go to end */
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movb (%eax,%esi), %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(3) /* yes, then exit */
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incl %eax /* increment pointer */
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decl %ecx /* decrement length counter */
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jz L(9) /* no more allowed => exit */
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movb (%eax,%esi), %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(3) /* yes, then exit */
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incl %eax /* increment pointer */
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decl %ecx /* decrement length counter */
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jz L(9) /* no more allowed => exit */
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movb (%eax,%esi), %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(3) /* yes, then exit */
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incl %eax /* increment pointer */
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jmp L(9) /* we don't have to test for counter underflow
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because we know we had a most 3 bytes
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remaining => exit */
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/* When coming from the main loop we have to adjust the pointer. */
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L(4): decl %ecx /* decrement counter */
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incl %eax /* increment pointer */
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L(5): decl %ecx /* increment pointer */
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incl %eax /* increment pointer */
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L(6): decl %ecx /* increment pointer */
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incl %eax /* increment pointer */
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L(7):
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addl $3, %ecx /* correct pre-decrementation of counter
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at the beginning of the loop; but why 3
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and not 4? Very simple, we have to count
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the NUL char we already wrote. */
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jz L(9) /* counter is also 0 => exit */
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/* We now have to fill the rest of the buffer with NUL. This
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is done in a tricky way. Please note that the addressing mode
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used below is not the same we used above. Here we use the
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%ecx register. */
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L(8):
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movb $0, (%ecx,%eax) /* store NUL char */
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L(3): decl %ecx /* all bytes written? */
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jnz L(8) /* no, then again */
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L(9): popl %esi /* restore saved register content */
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cfi_adjust_cfa_offset (-4)
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cfi_restore (esi)
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ret
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END (__stpncpy)
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libc_hidden_def (__stpncpy)
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weak_alias (__stpncpy, stpncpy)
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