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* improved comparebyte for small data amounts

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git-svn-id: trunk@17642 -
This commit is contained in:
florian 2011-06-02 20:02:26 +00:00
parent d8b80d2c23
commit b6aa04813e
1 changed files with 44 additions and 29 deletions
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73
rtl/i386/i386.inc
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@ -421,56 +421,71 @@ end;
{$ifndef FPC_SYSTEM_HAS_COMPAREBYTE}
{$define FPC_SYSTEM_HAS_COMPAREBYTE}
function CompareByte(Const buf1,buf2;len:SizeInt):SizeInt; assembler;
var
saveesi,saveedi : longint;
function CompareByte(Const buf1,buf2;len:SizeInt):SizeInt; assembler; nostackframe;
asm
movl %edi,saveedi
movl %esi,saveesi
cmpl $57,%ecx { empirically determined value on a Core 2 Duo Conroe }
jg .LCmpbyteFull
testl %ecx,%ecx
je .LCmpbyteZero
pushl %ebx
.LCmpbyteLoop:
movb (%eax),%bl
cmpb (%edx),%bl
leal 1(%eax),%eax
leal 1(%edx),%edx
jne .LCmpbyteExitFast
decl %ecx
jne .LCmpbyteLoop
.LCmpbyteExitFast:
movzbl -1(%edx),%ecx { Compare last position }
movzbl %bl,%eax
subl %ecx,%eax
popl %ebx
ret
.LCmpbyteZero:
movl $0,%eax
ret
.LCmpbyteFull:
pushl %esi
pushl %edi
cld
{$ifdef REGCALL}
movl %eax,%edi
movl %edx,%esi
movl %ecx,%eax
{$else}
movl buf2,%esi { Load params}
movl buf1,%edi
movl len,%eax
{$endif}
testl %eax,%eax {We address -1(%esi), so we have to deal with len=0}
je .LCmpbyteExit
cmpl $7,%eax {<7 not worth aligning and go through all trouble}
jl .LCmpbyte2
movl %edi,%ecx { Align on 32bits }
negl %ecx { calc bytes to align (%edi and 3) xor 3= -%edi and 3}
negl %ecx { calc bytes to align (%edi and 3) xor 3= -%edi and 3 }
andl $3,%ecx
subl %ecx,%eax { Subtract from number of bytes to go}
subl %ecx,%eax { Subtract from number of bytes to go }
orl %ecx,%ecx
rep
cmpsb {The actual 32-bit Aligning}
cmpsb { The actual 32-bit Aligning }
jne .LCmpbyte3
movl %eax,%ecx {bytes to do, divide by 4}
andl $3,%eax {remainder}
shrl $2,%ecx {The actual division}
orl %ecx,%ecx {Sets zero flag if ecx=0 -> no cmp}
movl %eax,%ecx { bytes to do, divide by 4 }
andl $3,%eax { remainder }
shrl $2,%ecx { The actual division }
orl %ecx,%ecx { Sets zero flag if ecx=0 -> no cmp }
rep
cmpsl
je .LCmpbyte2 { All equal? then to the left over bytes}
movl $4,%eax { Not equal. Rescan the last 4 bytes bytewise}
je .LCmpbyte2 { All equal? then to the left over bytes }
movl $4,%eax { Not equal. Rescan the last 4 bytes bytewise }
subl %eax,%esi
subl %eax,%edi
.LCmpbyte2:
movl %eax,%ecx {bytes still to (re)scan}
orl %eax,%eax {prevent disaster in case %eax=0}
movl %eax,%ecx { bytes still to (re)scan }
orl %eax,%eax { prevent disaster in case %eax=0 }
rep
cmpsb
.LCmpbyte3:
movzbl -1(%esi),%ecx
movzbl -1(%edi),%eax // Compare failing (or equal) position
movzbl -1(%edi),%eax { Compare failing (or equal) position }
subl %ecx,%eax
.LCmpbyteExit:
movl saveedi,%edi
movl saveesi,%esi
popl %edi
popl %esi
end;
{$endif FPC_SYSTEM_HAS_COMPAREBYTE}