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30891f35fa
We stopped adding "Contributed by" or similar lines in sources in 2012 in favour of git logs and keeping the Contributors section of the glibc manual up to date. Removing these lines makes the license header a bit more consistent across files and also removes the possibility of error in attribution when license blocks or files are copied across since the contributed-by lines don't actually reflect reality in those cases. Move all "Contributed by" and similar lines (Written by, Test by, etc.) into a new file CONTRIBUTED-BY to retain record of these contributions. These contributors are also mentioned in manual/contrib.texi, so we just maintain this additional record as a courtesy to the earlier developers. The following scripts were used to filter a list of files to edit in place and to clean up the CONTRIBUTED-BY file respectively. These were not added to the glibc sources because they're not expected to be of any use in future given that this is a one time task: https://gist.github.com/siddhesh/b5ecac94eabfd72ed2916d6d8157e7dc https://gist.github.com/siddhesh/15ea1f5e435ace9774f485030695ee02 Reviewed-by: Carlos O'Donell <carlos@redhat.com>
277 lines
11 KiB
ArmAsm
277 lines
11 KiB
ArmAsm
/* strchrnul (str, chr) -- Return pointer to first occurrence of CHR in STR
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or the final NUL byte.
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For Intel 80x86, x>=3.
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Copyright (C) 1994-2021 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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#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 STR RTN
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#define CHR STR+4
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.text
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ENTRY (__strchrnul)
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pushl %edi /* Save callee-safe registers used here. */
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cfi_adjust_cfa_offset (4)
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cfi_rel_offset (edi, 0)
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movl STR(%esp), %eax
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movl CHR(%esp), %edx
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/* At the moment %edx contains CHR. What we need for the
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algorithm is CHR in all bytes of the dword. Avoid
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operations on 16 bit words because these require an
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prefix byte (and one more cycle). */
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movb %dl, %dh /* now it is 0|0|c|c */
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movl %edx, %ecx
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shll $16, %edx /* now it is c|c|0|0 */
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movw %cx, %dx /* and finally c|c|c|c */
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/* Before we start with the main loop we process single bytes
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until the source pointer is aligned. This has two reasons:
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1. aligned 32-bit memory access is faster
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and (more important)
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2. we process in the main loop 32 bit in one step although
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we don't know the end of the string. But accessing at
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4-byte alignment guarantees that we never access illegal
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memory if this would not also be done by the trivial
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implementation (this is because all processor inherent
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boundaries are multiples of 4. */
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testb $3, %al /* correctly aligned ? */
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jz L(11) /* yes => begin loop */
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movb (%eax), %cl /* load byte in question (we need it twice) */
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cmpb %cl, %dl /* compare byte */
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je L(6) /* target found => return */
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testb %cl, %cl /* is NUL? */
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jz L(6) /* yes => return NULL */
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incl %eax /* increment pointer */
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testb $3, %al /* correctly aligned ? */
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jz L(11) /* yes => begin loop */
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movb (%eax), %cl /* load byte in question (we need it twice) */
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cmpb %cl, %dl /* compare byte */
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je L(6) /* target found => return */
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testb %cl, %cl /* is NUL? */
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jz L(6) /* yes => return NULL */
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incl %eax /* increment pointer */
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testb $3, %al /* correctly aligned ? */
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jz L(11) /* yes => begin loop */
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movb (%eax), %cl /* load byte in question (we need it twice) */
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cmpb %cl, %dl /* compare byte */
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je L(6) /* target found => return */
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testb %cl, %cl /* is NUL? */
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jz L(6) /* yes => return NULL */
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incl %eax /* increment pointer */
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/* No we have reached alignment. */
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jmp L(11) /* begin loop */
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/* We exit the loop if adding MAGIC_BITS to LONGWORD fails to
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change any of the hole bits of LONGWORD.
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1) Is this safe? Will it catch all the zero bytes?
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Suppose there is a byte with all zeros. Any carry bits
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propagating from its left will fall into the hole at its
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least significant bit and stop. Since there will be no
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carry from its most significant bit, the LSB of the
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byte to the left will be unchanged, and the zero will be
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detected.
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2) Is this worthwhile? Will it ignore everything except
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zero bytes? Suppose every byte of LONGWORD has a bit set
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somewhere. There will be a carry into bit 8. If bit 8
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is set, this will carry into bit 16. If bit 8 is clear,
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one of bits 9-15 must be set, so there will be a carry
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into bit 16. Similarly, there will be a carry into bit
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24. If one of bits 24-31 is set, there will be a carry
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into bit 32 (=carry flag), so all of the hole bits will
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be changed.
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3) But wait! Aren't we looking for CHR, not zero?
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Good point. So what we do is XOR LONGWORD with a longword,
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each of whose bytes is CHR. This turns each byte that is CHR
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into a zero. */
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/* Each round the main loop processes 16 bytes. */
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ALIGN(4)
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L(1): addl $16, %eax /* adjust pointer for whole round */
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L(11): movl (%eax), %ecx /* get word (= 4 bytes) in question */
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xorl %edx, %ecx /* XOR with word c|c|c|c => bytes of str == c
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are now 0 */
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movl $0xfefefeff, %edi /* magic value */
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addl %ecx, %edi /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* CHR */
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/* According to the algorithm we had to reverse the effect of the
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XOR first and then test the overflow bits. But because the
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following XOR would destroy the carry flag and it would (in a
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representation with more than 32 bits) not alter then last
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overflow, we can now test this condition. If no carry is signaled
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no overflow must have occurred in the last byte => it was 0. */
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jnc L(7)
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/* We are only interested in carry bits that change due to the
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previous add, so remove original bits */
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xorl %ecx, %edi /* ((word^charmask)+magic)^(word^charmask) */
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/* Now test for the other three overflow bits. */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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/* If at least one byte of the word is CHR we don't get 0 in %edi. */
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jnz L(7) /* found it => return pointer */
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/* Now we made sure the dword does not contain the character we are
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looking for. But because we deal with strings we have to check
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for the end of string before testing the next dword. */
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xorl %edx, %ecx /* restore original dword without reload */
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movl $0xfefefeff, %edi /* magic value */
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addl %ecx, %edi /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc L(7) /* highest byte is NUL => return NULL */
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xorl %ecx, %edi /* (word+magic)^word */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(7) /* found NUL => return NULL */
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movl 4(%eax), %ecx /* get word (= 4 bytes) in question */
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xorl %edx, %ecx /* XOR with word c|c|c|c => bytes of str == c
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are now 0 */
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movl $0xfefefeff, %edi /* magic value */
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addl %ecx, %edi /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* CHR */
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jnc L(71) /* highest byte is CHR => return pointer */
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xorl %ecx, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(71) /* found it => return pointer */
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xorl %edx, %ecx /* restore original dword without reload */
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movl $0xfefefeff, %edi /* magic value */
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addl %ecx, %edi /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc L(71) /* highest byte is NUL => return NULL */
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xorl %ecx, %edi /* (word+magic)^word */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(71) /* found NUL => return NULL */
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movl 8(%eax), %ecx /* get word (= 4 bytes) in question */
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xorl %edx, %ecx /* XOR with word c|c|c|c => bytes of str == c
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are now 0 */
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movl $0xfefefeff, %edi /* magic value */
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addl %ecx, %edi /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* CHR */
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jnc L(72) /* highest byte is CHR => return pointer */
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xorl %ecx, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(72) /* found it => return pointer */
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xorl %edx, %ecx /* restore original dword without reload */
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movl $0xfefefeff, %edi /* magic value */
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addl %ecx, %edi /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc L(72) /* highest byte is NUL => return NULL */
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xorl %ecx, %edi /* (word+magic)^word */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(72) /* found NUL => return NULL */
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movl 12(%eax), %ecx /* get word (= 4 bytes) in question */
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xorl %edx, %ecx /* XOR with word c|c|c|c => bytes of str == c
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are now 0 */
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movl $0xfefefeff, %edi /* magic value */
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addl %ecx, %edi /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* CHR */
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jnc L(73) /* highest byte is CHR => return pointer */
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xorl %ecx, %edi /* ((word^charmask)+magic)^(word^charmask) */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jnz L(73) /* found it => return pointer */
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xorl %edx, %ecx /* restore original dword without reload */
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movl $0xfefefeff, %edi /* magic value */
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addl %ecx, %edi /* add the magic value to the word. We get
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carry bits reported for each byte which
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is *not* 0 */
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jnc L(73) /* highest byte is NUL => return NULL */
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xorl %ecx, %edi /* (word+magic)^word */
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orl $0xfefefeff, %edi /* set all non-carry bits */
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incl %edi /* add 1: if one carry bit was *not* set
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the addition will not result in 0. */
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jz L(1) /* no NUL found => restart loop */
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L(73): addl $4, %eax /* adjust pointer */
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L(72): addl $4, %eax
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L(71): addl $4, %eax
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/* We now scan for the byte in which the character was matched.
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But we have to take care of the case that a NUL char is
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found before this in the dword. */
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L(7): testb %cl, %cl /* is first byte CHR? */
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jz L(6) /* yes => return pointer */
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cmpb %dl, %cl /* is first byte NUL? */
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je L(6) /* yes => return NULL */
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incl %eax /* it's not in the first byte */
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testb %ch, %ch /* is second byte CHR? */
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jz L(6) /* yes => return pointer */
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cmpb %dl, %ch /* is second byte NUL? */
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je L(6) /* yes => return NULL? */
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incl %eax /* it's not in the second byte */
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shrl $16, %ecx /* make upper byte accessible */
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testb %cl, %cl /* is third byte CHR? */
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jz L(6) /* yes => return pointer */
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cmpb %dl, %cl /* is third byte NUL? */
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je L(6) /* yes => return NULL */
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/* It must be in the fourth byte and it cannot be NUL. */
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incl %eax
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L(6): popl %edi /* restore saved register content */
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cfi_adjust_cfa_offset (-4)
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cfi_restore (edi)
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ret
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END (__strchrnul)
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weak_alias (__strchrnul, strchrnul)
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