112 lines
2.0 KiB
ArmAsm
112 lines
2.0 KiB
ArmAsm
/*
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* Written by J.T. Conklin <jtc@acorntoolworks.com>
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* Public domain.
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*/
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#include <machine/asm.h>
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__FBSDID("$FreeBSD$");
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#if 0
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RCSID("$NetBSD: strcpy.S,v 1.3 2004/07/19 20:04:41 drochner Exp $")
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#endif
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/*
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* This strcpy implementation copies a byte at a time until the
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* source pointer is aligned to a word boundary, it then copies by
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* words until it finds a word containing a zero byte, and finally
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* copies by bytes until the end of the string is reached.
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*
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* While this may result in unaligned stores if the source and
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* destination pointers are unaligned with respect to each other,
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* it is still faster than either byte copies or the overhead of
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* an implementation suitable for machines with strict alignment
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* requirements.
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*/
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ENTRY(strcpy)
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movq %rdi,%rax
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movabsq $0x0101010101010101,%r8
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movabsq $0x8080808080808080,%r9
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/*
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* Align source to a word boundary.
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* Consider unrolling loop?
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*/
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.Lalign:
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testb $7,%sil
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je .Lword_aligned
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movb (%rsi),%dl
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incq %rsi
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl
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jne .Lalign
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ret
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.p2align 4
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.Lloop:
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movq %rdx,(%rdi)
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addq $8,%rdi
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.Lword_aligned:
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movq (%rsi),%rdx
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movq %rdx,%rcx
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addq $8,%rsi
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subq %r8,%rcx
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testq %r9,%rcx
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je .Lloop
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/*
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* In rare cases, the above loop may exit prematurely. We must
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* return to the loop if none of the bytes in the word equal 0.
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*/
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl /* 1st byte == 0? */
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je .Ldone
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shrq $8,%rdx
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl /* 2nd byte == 0? */
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je .Ldone
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shrq $8,%rdx
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl /* 3rd byte == 0? */
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je .Ldone
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shrq $8,%rdx
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl /* 4th byte == 0? */
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je .Ldone
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shrq $8,%rdx
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl /* 5th byte == 0? */
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je .Ldone
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shrq $8,%rdx
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl /* 6th byte == 0? */
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je .Ldone
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shrq $8,%rdx
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl /* 7th byte == 0? */
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je .Ldone
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shrq $8,%rdx
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movb %dl,(%rdi)
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incq %rdi
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testb %dl,%dl /* 8th byte == 0? */
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jne .Lword_aligned
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.Ldone:
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ret
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