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9d8e22777e
While hard to measure, reducing the number of possibly/likely mis-predicted branches can generally be expected to be slightly better. Other than apparent at the first glance, this also doesn't grow the function size (the alignment gap to the next function just gets smaller). Signed-off-by: Jan Beulich <jbeulich@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/4F218584020000780006F422@nat28.tlf.novell.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
207 lines
4.1 KiB
ArmAsm
207 lines
4.1 KiB
ArmAsm
/* Copyright 2002 Andi Kleen */
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#include <linux/linkage.h>
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#include <asm/cpufeature.h>
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#include <asm/dwarf2.h>
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#include <asm/alternative-asm.h>
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/*
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* memcpy - Copy a memory block.
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*
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* Input:
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* rdi destination
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* rsi source
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* rdx count
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*
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* Output:
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* rax original destination
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*/
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/*
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* memcpy_c() - fast string ops (REP MOVSQ) based variant.
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*
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* This gets patched over the unrolled variant (below) via the
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* alternative instructions framework:
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*/
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.section .altinstr_replacement, "ax", @progbits
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.Lmemcpy_c:
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movq %rdi, %rax
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movq %rdx, %rcx
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shrq $3, %rcx
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andl $7, %edx
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rep movsq
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movl %edx, %ecx
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rep movsb
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ret
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.Lmemcpy_e:
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.previous
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/*
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* memcpy_c_e() - enhanced fast string memcpy. This is faster and simpler than
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* memcpy_c. Use memcpy_c_e when possible.
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*
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* This gets patched over the unrolled variant (below) via the
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* alternative instructions framework:
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*/
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.section .altinstr_replacement, "ax", @progbits
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.Lmemcpy_c_e:
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movq %rdi, %rax
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movq %rdx, %rcx
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rep movsb
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ret
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.Lmemcpy_e_e:
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.previous
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ENTRY(__memcpy)
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ENTRY(memcpy)
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CFI_STARTPROC
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movq %rdi, %rax
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cmpq $0x20, %rdx
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jb .Lhandle_tail
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/*
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* We check whether memory false dependence could occur,
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* then jump to corresponding copy mode.
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*/
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cmp %dil, %sil
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jl .Lcopy_backward
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subq $0x20, %rdx
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.Lcopy_forward_loop:
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subq $0x20, %rdx
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/*
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* Move in blocks of 4x8 bytes:
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*/
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movq 0*8(%rsi), %r8
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movq 1*8(%rsi), %r9
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movq 2*8(%rsi), %r10
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movq 3*8(%rsi), %r11
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leaq 4*8(%rsi), %rsi
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movq %r8, 0*8(%rdi)
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movq %r9, 1*8(%rdi)
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movq %r10, 2*8(%rdi)
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movq %r11, 3*8(%rdi)
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leaq 4*8(%rdi), %rdi
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jae .Lcopy_forward_loop
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addl $0x20, %edx
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jmp .Lhandle_tail
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.Lcopy_backward:
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/*
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* Calculate copy position to tail.
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*/
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addq %rdx, %rsi
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addq %rdx, %rdi
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subq $0x20, %rdx
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/*
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* At most 3 ALU operations in one cycle,
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* so append NOPS in the same 16bytes trunk.
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*/
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.p2align 4
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.Lcopy_backward_loop:
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subq $0x20, %rdx
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movq -1*8(%rsi), %r8
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movq -2*8(%rsi), %r9
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movq -3*8(%rsi), %r10
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movq -4*8(%rsi), %r11
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leaq -4*8(%rsi), %rsi
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movq %r8, -1*8(%rdi)
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movq %r9, -2*8(%rdi)
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movq %r10, -3*8(%rdi)
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movq %r11, -4*8(%rdi)
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leaq -4*8(%rdi), %rdi
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jae .Lcopy_backward_loop
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/*
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* Calculate copy position to head.
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*/
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addl $0x20, %edx
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subq %rdx, %rsi
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subq %rdx, %rdi
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.Lhandle_tail:
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cmpl $16, %edx
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jb .Lless_16bytes
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/*
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* Move data from 16 bytes to 31 bytes.
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*/
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movq 0*8(%rsi), %r8
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movq 1*8(%rsi), %r9
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movq -2*8(%rsi, %rdx), %r10
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movq -1*8(%rsi, %rdx), %r11
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movq %r8, 0*8(%rdi)
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movq %r9, 1*8(%rdi)
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movq %r10, -2*8(%rdi, %rdx)
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movq %r11, -1*8(%rdi, %rdx)
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retq
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.p2align 4
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.Lless_16bytes:
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cmpl $8, %edx
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jb .Lless_8bytes
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/*
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* Move data from 8 bytes to 15 bytes.
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*/
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movq 0*8(%rsi), %r8
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movq -1*8(%rsi, %rdx), %r9
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movq %r8, 0*8(%rdi)
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movq %r9, -1*8(%rdi, %rdx)
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retq
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.p2align 4
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.Lless_8bytes:
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cmpl $4, %edx
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jb .Lless_3bytes
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/*
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* Move data from 4 bytes to 7 bytes.
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*/
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movl (%rsi), %ecx
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movl -4(%rsi, %rdx), %r8d
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movl %ecx, (%rdi)
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movl %r8d, -4(%rdi, %rdx)
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retq
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.p2align 4
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.Lless_3bytes:
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subl $1, %edx
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jb .Lend
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/*
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* Move data from 1 bytes to 3 bytes.
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*/
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movzbl (%rsi), %ecx
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jz .Lstore_1byte
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movzbq 1(%rsi), %r8
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movzbq (%rsi, %rdx), %r9
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movb %r8b, 1(%rdi)
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movb %r9b, (%rdi, %rdx)
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.Lstore_1byte:
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movb %cl, (%rdi)
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.Lend:
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retq
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CFI_ENDPROC
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ENDPROC(memcpy)
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ENDPROC(__memcpy)
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/*
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* Some CPUs are adding enhanced REP MOVSB/STOSB feature
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* If the feature is supported, memcpy_c_e() is the first choice.
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* If enhanced rep movsb copy is not available, use fast string copy
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* memcpy_c() when possible. This is faster and code is simpler than
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* original memcpy().
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* Otherwise, original memcpy() is used.
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* In .altinstructions section, ERMS feature is placed after REG_GOOD
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* feature to implement the right patch order.
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*
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* Replace only beginning, memcpy is used to apply alternatives,
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* so it is silly to overwrite itself with nops - reboot is the
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* only outcome...
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*/
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.section .altinstructions, "a"
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altinstruction_entry memcpy,.Lmemcpy_c,X86_FEATURE_REP_GOOD,\
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.Lmemcpy_e-.Lmemcpy_c,.Lmemcpy_e-.Lmemcpy_c
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altinstruction_entry memcpy,.Lmemcpy_c_e,X86_FEATURE_ERMS, \
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.Lmemcpy_e_e-.Lmemcpy_c_e,.Lmemcpy_e_e-.Lmemcpy_c_e
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.previous
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