Re: [FFmpeg-devel] [PATCH 07/12] mips/aacdec: remove uses of mips32r2 specific ext instructions

[Nedeljko Babic]

 Removing these removes the dependency of this code on mips32r2 which would
 allow it to be used on processors which have FPU instructions, but not r2
 instructions (like the mips64el debian port for instance).
 
 
 I would be more comfortable if there were two instances of this code: one for
 mips32r2 and one for mips32 so advantages of using mips32r2 instructions 
 (however small here) are left intact.
 
 On the other hand, since this doesn't change much number of instructions used
 (adding at maximum around 100 instructions overall if I am not mistaking) I 
 am ok with this.

Well I can't see how 'ext' can ever be faster than 'and' (it does more
work) so most of these should be no slower anyway. For VMUL4S my version
has 2 extra instructions in it so it could be a bit slower. Does this
#if seem ok?

I never said that 'ext' is faster than 'and'.
This code was written so that the pipeline stalls are eliminated (or reduced to 
a minimum).
Taking this in consideration it is not important which instruction is faster 
overall.

Maybe I was not clear, but I said that I am ok with your first patch.
It is true that you only have 2 extra instructions in VMUL4S and I don't have a 
problem with that.

Regarding your question about #if, this is even better than original patch from 
my point of view,
but you should use HAVE_MIPS32R2 in this case.

- Nedeljko
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Re: [FFmpeg-devel] [PATCH 07/12] mips/aacdec: remove uses of mips32r2 specific ext instructions

[James Cowgill]

On Tue, 2015-03-03 at 12:42 +, Nedeljko Babic wrote:
 Removing these removes the dependency of this code on mips32r2 which would
 allow it to be used on processors which have FPU instructions, but not r2
 instructions (like the mips64el debian port for instance).
 
 
 I would be more comfortable if there were two instances of this code: one for
 mips32r2 and one for mips32 so advantages of using mips32r2 instructions 
 (however small here) are left intact.
 
 On the other hand, since this doesn't change much number of instructions used
 (adding at maximum around 100 instructions overall if I am not mistaking) I 
 am ok with this.

Well I can't see how 'ext' can ever be faster than 'and' (it does more
work) so most of these should be no slower anyway. For VMUL4S my version
has 2 extra instructions in it so it could be a bit slower. Does this
#if seem ok?

--- a/libavcodec/mips/aacdec_mips.h
+++ b/libavcodec/mips/aacdec_mips.h
@@ -198,9 +198,18 @@ static inline float *VMUL4S_mips(float *dst, const float 
*v, unsigned idx,
 lwxc1   %[temp12],  %[temp3](%[v])\n\t
 lwxc1   %[temp13],  %[temp4](%[v])\n\t
 and %[temp1],   %[sign],  %[mask] \n\t
+#if defined(__mips_isa_rev)  __mips_isa_rev = 2
 ext %[temp2],   %[idx],   12, 1   \n\t
 ext %[temp3],   %[idx],   13, 1   \n\t
 ext %[temp4],   %[idx],   14, 1   \n\t
+#else
+srl %[temp2],   %[idx],   12  \n\t
+srl %[temp3],   %[idx],   13  \n\t
+srl %[temp4],   %[idx],   14  \n\t
+andi%[temp2],   %[temp2], 1   \n\t
+andi%[temp3],   %[temp3], 1   \n\t
+andi%[temp4],   %[temp4], 1   \n\t
+#endif
 sllv%[sign],%[sign],  %[temp2]\n\t
 xor %[temp1],   %[temp0], %[temp1]\n\t
 and %[temp2],   %[sign],  %[mask] \n\t

Thanks,
James

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