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diff --git a/libc/string/x86_64/strspn.S b/libc/string/x86_64/strspn.S
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+/* strspn (str, ss) -- Return the length of the initial segment of STR
+ which contains only characters from SS.
+ For AMD x86-64.
+ Copyright (C) 1994-1997, 2000, 2002, 2003, 2004, 2005
+ Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>.
+ Bug fixes by Alan Modra <Alan@SPRI.Levels.UniSA.Edu.Au>.
+ Adopted for x86-64 by Andreas Jaeger <aj@suse.de>.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+#include "_glibc_inc.h"
+
+ .text
+ENTRY (strspn)
+
+ movq %rdi, %rdx /* Save SRC. */
+
+ /* First we create a table with flags for all possible characters.
+ For the ASCII (7bit/8bit) or ISO-8859-X character sets which are
+ supported by the C string functions we have 256 characters.
+ Before inserting marks for the stop characters we clear the whole
+ table. */
+ movq %rdi, %r8 /* Save value. */
+ subq $256, %rsp /* Make space for 256 bytes. */
+ movl $32, %ecx /* 32*8 bytes = 256 bytes. */
+ movq %rsp, %rdi
+ xorl %eax, %eax /* We store 0s. */
+ cld
+ rep
+ stosq
+
+ movq %rsi, %rax /* Setup stopset. */
+
+/* For understanding the following code remember that %rcx == 0 now.
+ Although all the following instruction only modify %cl we always
+ have a correct zero-extended 64-bit value in %rcx. */
+
+ .p2align 4
+L(2): movb (%rax), %cl /* get byte from stopset */
+ testb %cl, %cl /* is NUL char? */
+ jz L(1) /* yes => start compare loop */
+ movb %cl, (%rsp,%rcx) /* set corresponding byte in stopset table */
+
+ movb 1(%rax), %cl /* get byte from stopset */
+ testb $0xff, %cl /* is NUL char? */
+ jz L(1) /* yes => start compare loop */
+ movb %cl, (%rsp,%rcx) /* set corresponding byte in stopset table */
+
+ movb 2(%rax), %cl /* get byte from stopset */
+ testb $0xff, %cl /* is NUL char? */
+ jz L(1) /* yes => start compare loop */
+ movb %cl, (%rsp,%rcx) /* set corresponding byte in stopset table */
+
+ movb 3(%rax), %cl /* get byte from stopset */
+ addq $4, %rax /* increment stopset pointer */
+ movb %cl, (%rsp,%rcx) /* set corresponding byte in stopset table */
+ testb $0xff, %cl /* is NUL char? */
+ jnz L(2) /* no => process next dword from stopset */
+
+L(1): leaq -4(%rdx), %rax /* prepare loop */
+
+ /* We use a neat trick for the following loop. Normally we would
+ have to test for two termination conditions
+ 1. a character in the stopset was found
+ and
+ 2. the end of the string was found
+ But as a sign that the character is in the stopset we store its
+ value in the table. But the value of NUL is NUL so the loop
+ terminates for NUL in every case. */
+
+ .p2align 4
+L(3): addq $4, %rax /* adjust pointer for full loop round */
+
+ movb (%rax), %cl /* get byte from string */
+ testb %cl, (%rsp,%rcx) /* is it contained in skipset? */
+ jz L(4) /* no => return */
+
+ movb 1(%rax), %cl /* get byte from string */
+ testb %cl, (%rsp,%rcx) /* is it contained in skipset? */
+ jz L(5) /* no => return */
+
+ movb 2(%rax), %cl /* get byte from string */
+ testb %cl, (%rsp,%rcx) /* is it contained in skipset? */
+ jz L(6) /* no => return */
+
+ movb 3(%rax), %cl /* get byte from string */
+ testb %cl, (%rsp,%rcx) /* is it contained in skipset? */
+ jnz L(3) /* yes => start loop again */
+
+ incq %rax /* adjust pointer */
+L(6): incq %rax
+L(5): incq %rax
+
+L(4): addq $256, %rsp /* remove stopset */
+ subq %rdx, %rax /* we have to return the number of valid
+ characters, so compute distance to first
+ non-valid character */
+ ret
+END (strspn)