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Faster Len(String$) with asm
Posted: Sat Oct 14, 2006 6:06 am
by Helle
And here a example for Len(String$) with asm (need min. pentium 4):
Code: Select all
;- "Helle" Klaus Helbing, 14.10.2006, PB4.00
Global X.l
Global Len.l
Global String$ = "pokjhgskioUIOHR%(!ยง)AGJOjiioe328959askfakgj9e6t306rgrjhg409604tkmgoe"
;-------- Test with SSE
TestTime.l = ElapsedMilliseconds()
X = @String$ ;string-pointer
For i = 1 To 10000000
!mov ebx,[v_X]
!pxor xmm1,xmm1 ;xmm1 null
W1:
!movdqu xmm0,[ebx] ;read 16 byte of string
!add ebx,16
!pcmpeqb xmm0,xmm1 ;compare the 16 bytes of xmm0 with null (xmm1), set byte = 255 if equal (= null) and byte = 0 if not equal
!pmovmskb eax,xmm0 ;copy signum-bits to eax (ax)
!or eax,eax ;null ?
!jz l_w1 ;yes, not found the null-byte of string (end of string)
!sub ebx,17
!test al,255
!jnz l_w2
!xchg al,ah
!add ebx,8
W2:
!inc ebx
!shr ax,1
!jnc l_w2
Next
!sub ebx,[v_X]
!mov [v_Len],ebx
Time = ElapsedMilliseconds() - TestTime
MessageRequester("Len(String) with SSE","Stringlength = " + Str(Len) + Chr(13) + "TestTime = " + Str(Time) + " ms")
;-------- Test with PB
TestTime.l = ElapsedMilliseconds()
For i = 1 To 10000000
Len = Len(String$)
Next
Time = ElapsedMilliseconds() - TestTime
MessageRequester("Len(String) with PB","Stringlength = " + Str(Len) + Chr(13) + "TestTime = " + Str(Time) + " ms")
End
Greeting
Helle
Posted: Sat Oct 14, 2006 11:03 am
by wilbert
It looks nice but on my computer (Athlon processor) it doesn't work.
Your example works fine but if I try a string with a length of 10 characters, it returns 19. The pcmpeqb instruction doesn't seem to support 128 bit comparisson only 64.
Posted: Sat Oct 14, 2006 1:08 pm
by Helle
My example need SSE2.
PCMPEQB support 128 bit with processors with SSE2 (from P4, Celeron with Willamette-Core, Athlon 64, Opteron or Sempron with Paris-Core).
Greeting
Helle
Posted: Sat Oct 21, 2006 8:10 am
by wilbert
Those SSE instructions are very useful
I adapted your example to use only SSE instructions and no SSE2 so it also works on my Athlon CPU. I also implemented a second parameter. If the length of the string is bigger then that value, it returns that value.
Code: Select all
Procedure.l Len_SSE_(*String.l, MaxLen.l = -1)
!mov edx,[p.p_String]
!mov ecx,[p.v_MaxLen]
!push ecx
!add ecx,edx
!cmp edx,ecx
!jna len_sse_maxok
!mov ecx,$ffffffff
!len_sse_maxok:
!pxor mm0,mm0
!movq mm1,[edx]
!pcmpeqb mm1,mm0
!pmovmskb eax,mm1
!and al,al
!jnz len_sse_cont
!and edx,$fffffff8
!len_sse_loop:
!add edx,8
!cmp edx,ecx
!jae len_sse_cont
!movq mm1,[edx]
!pcmpeqb mm1,mm0
!pmovmskb eax,mm1
!and al,al
!jz len_sse_loop
!len_sse_cont:
!emms
!pop ecx
!bsf eax,eax
!add eax,edx
!sub eax,[p.p_String]
!cmp eax,ecx
!jna len_sse_cont2
!mov eax,ecx
!len_sse_cont2:
ProcedureReturn
EndProcedure
Macro Len_SSE(String, MaxLen = -1)
Len_SSE_(@String, MaxLen)
EndMacro
If for example you only want to know if the string is at least 20 characters long, you can check if Len_SSE(String$,20) equals 20.
It can speed things up a lot for large strings.