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lib/libc/amd64/string/strcspn.S: fix behaviour with sets of 17--32

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When a string is matched against a set of 17--32 characters, each chunk
of the string is matched first against the first 16 characters of the
set and then against the remaining characters.  We also check at the
same time if the string has a nul byte in the current chunk, terminating
the search if it does.

Due to misconceived logic, the order of checks was "first half of set,
nul byte, second half of set", meaning that a match with the second half
of the set was ignored when the string ended in the same 16 bytes.
Reverse the order of checks to fix this problem.

Sponsored by:	The FreeBSD Foundation
Approved by:	mjg (blanket, via IRC)
MFC after:	1 week
MFC to:		stable/14
This commit is contained in:
Robert Clausecker 2023-09-11 19:56:30 -04:00
parent fafb03ab42
commit 52d4a4d4e0
1 changed files with 15 additions and 10 deletions
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25
lib/libc/amd64/string/strcspn.S
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@ -259,27 +259,32 @@ ARCHENTRY(strcspn, x86_64_v2)
movdqu 48(%rsp, %rcx, 1), %xmm3 # second part of set
/* set is 17--32 bytes in size */
pcmpistri $0, %xmm0, %xmm2 # match in head?
jbe .Lheadmatchv2
pcmpistri $0, %xmm0, %xmm3 # ZF=1 not possible here
pcmpistri $0, %xmm0, %xmm2 # match in first set half?
jb .Lheadmatchv2
pcmpistri $0, %xmm0, %xmm3 # match in second set half or end of string?
jbe .Lheadmatchv2
ALIGN_TEXT
0: movdqa (%rax), %xmm0
pcmpistri $0, %xmm0, %xmm2
jbe 1b
jb 2f # match in first set half?
pcmpistri $0, %xmm0, %xmm3
jb 1f # ZF=1 not possible here
jbe 1f # match in second set half or end of string?
movdqa 16(%rax), %xmm0
add $32, %rax
pcmpistri $0, %xmm0, %xmm2
jbe 3b
jb 3f # match in first set half?
pcmpistri $0, %xmm0, %xmm3
jae 0b # ZF=1 not possible here
ja 0b # neither match in 2nd half nor string end?
sub $16, %rax # go back to second half
1: add %rcx, %rax
sub %rdi, %rax
3: lea -16(%rax), %rax # go back to second half
1: jc 2f # jump if match found
pxor %xmm1, %xmm1
pcmpeqb %xmm1, %xmm0 # where is the NUL byte?
pmovmskb %xmm0, %ecx
tzcnt %ecx, %ecx # location of NUL byte in (%rax)
2: sub %rdi, %rax # offset of %xmm0 from beginning of string
add %rcx, %rax # prefix length before match/NUL
leave
ret