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

[James Cowgill]

On Tue, 2015-03-03 at 12:42 +0000, 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