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53 lines
1.0 KiB
NASM
53 lines
1.0 KiB
NASM
/* Copyright (C) 1995 DJ Delorie, see COPYING.DJ for details */
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##include<libc/asm.h>
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# .file "memset.s"
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.text
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.global _memset
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.align 4
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_memset:
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pushl %ebp
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movl %esp,%ebp
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pushl %edi
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movl 8(%ebp),%edi
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movl 12(%ebp),%eax
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movl 16(%ebp),%ecx
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cld
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# We will handle memsets of <= 15 bytes one byte at a time.
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# This avoids some extra overhead for small memsets, and
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# knowing we are setting > 15 bytes eliminates some annoying
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# checks in the "long move" case.
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cmpl $15,%ecx
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jle L3
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# Otherwise, tile the byte value out into %eax.
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# 0x41 -> 0x41414141, etc.
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movb %al,%ah
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movl %eax,%edx
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sall $16,%eax
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movw %dx,%ax
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jmp L2
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# Handle any cruft necessary to get %edi long-aligned.
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L1: stosb
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decl %ecx
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L2: testl $3,%edi
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jnz L1
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# Now slam out all of the longs.
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movl %ecx,%edx
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shrl $2,%ecx
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rep
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stosl
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# Finally, handle any trailing cruft. We know the high three bytes
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# of %ecx must be zero, so just put the "slop count" in the low byte.
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movb %dl,%cl
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andb $3,%cl
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L3: rep
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stosb
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popl %edi
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movl 8(%ebp),%eax
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leave
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ret
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