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08cbcd4dbc
No bug. The way wcsnlen will check if near the end of maxlen is the following macro: mov %r11, %rsi; \ subq %rax, %rsi; \ andq $-64, %rax; \ testq $-64, %rsi; \ je L(strnlen_ret) Which words independently of s + maxlen overflowing. So the second overflow check is unnecissary for correctness and just extra overhead in the common no overflow case. test-strlen.c, test-wcslen.c, test-strnlen.c and test-wcsnlen.c are all passing Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
264 lines
5.2 KiB
ArmAsm
264 lines
5.2 KiB
ArmAsm
/* SSE2 version of strlen and SSE4.1 version of wcslen.
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Copyright (C) 2012-2021 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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#ifdef AS_WCSLEN
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# define PMINU pminud
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# define PCMPEQ pcmpeqd
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# define SHIFT_RETURN shrq $2, %rax
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#else
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# define PMINU pminub
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# define PCMPEQ pcmpeqb
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# define SHIFT_RETURN
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#endif
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/* Long lived register in strlen(s), strnlen(s, n) are:
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%xmm3 - zero
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%rdi - s
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%r10 (s+n) & (~(64-1))
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%r11 s+n
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*/
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.text
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ENTRY(strlen)
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/* Test 64 bytes from %rax for zero. Save result as bitmask in %rdx. */
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#define FIND_ZERO \
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PCMPEQ (%rax), %xmm0; \
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PCMPEQ 16(%rax), %xmm1; \
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PCMPEQ 32(%rax), %xmm2; \
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PCMPEQ 48(%rax), %xmm3; \
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pmovmskb %xmm0, %esi; \
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pmovmskb %xmm1, %edx; \
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pmovmskb %xmm2, %r8d; \
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pmovmskb %xmm3, %ecx; \
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salq $16, %rdx; \
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salq $16, %rcx; \
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orq %rsi, %rdx; \
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orq %r8, %rcx; \
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salq $32, %rcx; \
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orq %rcx, %rdx;
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#ifdef AS_STRNLEN
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/* Do not read anything when n==0. */
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test %RSI_LP, %RSI_LP
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jne L(n_nonzero)
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xor %rax, %rax
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ret
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L(n_nonzero):
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# ifdef AS_WCSLEN
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/* Check for overflow from maxlen * sizeof(wchar_t). If it would
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overflow the only way this program doesn't have undefined behavior
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is if there is a null terminator in valid memory so wcslen will
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suffice. */
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mov %RSI_LP, %R10_LP
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sar $62, %R10_LP
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jnz __wcslen_sse4_1
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sal $2, %RSI_LP
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# endif
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/* Initialize long lived registers. */
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add %RDI_LP, %RSI_LP
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mov %RSI_LP, %R10_LP
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and $-64, %R10_LP
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mov %RSI_LP, %R11_LP
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#endif
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pxor %xmm0, %xmm0
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pxor %xmm1, %xmm1
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pxor %xmm2, %xmm2
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pxor %xmm3, %xmm3
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movq %rdi, %rax
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movq %rdi, %rcx
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andq $4095, %rcx
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/* Offsets 4032-4047 will be aligned into 4032 thus fit into page. */
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cmpq $4047, %rcx
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/* We cannot unify this branching as it would be ~6 cycles slower. */
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ja L(cross_page)
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#ifdef AS_STRNLEN
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/* Test if end is among first 64 bytes. */
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# define STRNLEN_PROLOG \
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mov %r11, %rsi; \
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subq %rax, %rsi; \
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andq $-64, %rax; \
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testq $-64, %rsi; \
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je L(strnlen_ret)
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#else
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# define STRNLEN_PROLOG andq $-64, %rax;
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#endif
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/* Ignore bits in mask that come before start of string. */
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#define PROLOG(lab) \
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movq %rdi, %rcx; \
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xorq %rax, %rcx; \
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STRNLEN_PROLOG; \
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sarq %cl, %rdx; \
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test %rdx, %rdx; \
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je L(lab); \
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bsfq %rdx, %rax; \
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SHIFT_RETURN; \
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ret
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#ifdef AS_STRNLEN
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andq $-16, %rax
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FIND_ZERO
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#else
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/* Test first 16 bytes unaligned. */
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movdqu (%rax), %xmm4
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PCMPEQ %xmm0, %xmm4
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pmovmskb %xmm4, %edx
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test %edx, %edx
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je L(next48_bytes)
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bsf %edx, %eax /* If eax is zeroed 16bit bsf can be used. */
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SHIFT_RETURN
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ret
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L(next48_bytes):
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/* Same as FIND_ZERO except we do not check first 16 bytes. */
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andq $-16, %rax
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PCMPEQ 16(%rax), %xmm1
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PCMPEQ 32(%rax), %xmm2
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PCMPEQ 48(%rax), %xmm3
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pmovmskb %xmm1, %edx
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pmovmskb %xmm2, %r8d
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pmovmskb %xmm3, %ecx
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salq $16, %rdx
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salq $16, %rcx
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orq %r8, %rcx
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salq $32, %rcx
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orq %rcx, %rdx
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#endif
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/* When no zero byte is found xmm1-3 are zero so we do not have to
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zero them. */
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PROLOG(loop)
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.p2align 4
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L(cross_page):
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andq $-64, %rax
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FIND_ZERO
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PROLOG(loop_init)
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#ifdef AS_STRNLEN
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/* We must do this check to correctly handle strnlen (s, -1). */
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L(strnlen_ret):
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bts %rsi, %rdx
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sarq %cl, %rdx
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test %rdx, %rdx
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je L(loop_init)
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bsfq %rdx, %rax
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SHIFT_RETURN
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ret
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#endif
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.p2align 4
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L(loop_init):
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pxor %xmm1, %xmm1
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pxor %xmm2, %xmm2
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pxor %xmm3, %xmm3
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#ifdef AS_STRNLEN
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.p2align 4
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L(loop):
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addq $64, %rax
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cmpq %rax, %r10
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je L(exit_end)
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movdqa (%rax), %xmm0
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PMINU 16(%rax), %xmm0
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PMINU 32(%rax), %xmm0
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PMINU 48(%rax), %xmm0
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PCMPEQ %xmm3, %xmm0
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pmovmskb %xmm0, %edx
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testl %edx, %edx
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jne L(exit)
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jmp L(loop)
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.p2align 4
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L(exit_end):
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cmp %rax, %r11
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je L(first) /* Do not read when end is at page boundary. */
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pxor %xmm0, %xmm0
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FIND_ZERO
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L(first):
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bts %r11, %rdx
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bsfq %rdx, %rdx
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addq %rdx, %rax
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subq %rdi, %rax
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SHIFT_RETURN
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ret
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.p2align 4
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L(exit):
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pxor %xmm0, %xmm0
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FIND_ZERO
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bsfq %rdx, %rdx
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addq %rdx, %rax
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subq %rdi, %rax
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SHIFT_RETURN
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ret
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#else
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/* Main loop. Unrolled twice to improve L2 cache performance on core2. */
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.p2align 4
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L(loop):
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movdqa 64(%rax), %xmm0
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PMINU 80(%rax), %xmm0
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PMINU 96(%rax), %xmm0
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PMINU 112(%rax), %xmm0
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PCMPEQ %xmm3, %xmm0
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pmovmskb %xmm0, %edx
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testl %edx, %edx
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jne L(exit64)
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subq $-128, %rax
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movdqa (%rax), %xmm0
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PMINU 16(%rax), %xmm0
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PMINU 32(%rax), %xmm0
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PMINU 48(%rax), %xmm0
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PCMPEQ %xmm3, %xmm0
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pmovmskb %xmm0, %edx
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testl %edx, %edx
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jne L(exit0)
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jmp L(loop)
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.p2align 4
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L(exit64):
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addq $64, %rax
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L(exit0):
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pxor %xmm0, %xmm0
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FIND_ZERO
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bsfq %rdx, %rdx
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addq %rdx, %rax
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subq %rdi, %rax
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SHIFT_RETURN
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ret
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#endif
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END(strlen)
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