SSE shufps helper snippet

[daydreamer]

shufps is hard to find the right immediate byte you want, so I am making a helper program
but immediate byte = I need to selfmodify it to find the right
this for starters is a snippet that makes it possible to singlestep to understand SHUFPS better

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.data
ALIGN 16
tstf    REAL4 1.0,2.0,3.0,4.0
tstf2   REAL4 21.0,22.0,23.0,24.0
tstf3   REAL4 1.0,2.0,3.0,4.0
tstf4   REAL4 21.0,22.0,23.0,24.0
.code

@@l1:  finit
       DB 0F0H ;anything that causes protection fault and start your debugger to singlestep this
       NOP
       MOVAPS XMM4,[tstf3]
       MOVAPS XMM5,[tstf4]
       
imb:  SHUFPS XMM4,XMM5,255
       MOVAPS [tstf],XMM4
       MOVAPS [tstf2],XMM5
       fld tstf ;view result in debugger in fp regs, if it doesnt support showing .xmm
       fld tstf+4
       fld tstf+8
       fld tstf+12
       fld tstf2
       fld tstf2+4
       fld tstf2+8
       fld tstf2+12
       lea ebx,[imb+3] ;cant make this work
       dec BYTE PTR [ebx]
       jne @@l1           


I searched the old forum for how to make .code segment writable, but couldnt find anything
dec causes a violation access
could appreciate some help

[Mark_Larson]

 Good to see someone doing some sample code.  :)  However as a bit of constructive criticism, you should use a hex or binary value for the immediate when using SHUFPS.  I usuallyuse binary because it makes it very easy to understand, since it specifies which dword in binary to use from the destination and source.

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;for the purposes of the comments, all "Dwords" are 0 based.  So dword 0 is the first one.  dword 1 is the second, and so on.
shufps xmm0,xmm1,01010101b          ;blast dword 1 of destination to first 2 dwords in destination, blast dword 1 of source to last 2 dwords in destination