[FFmpeg-devel] [PATCH 2/7] ARM: NEON optimised simple_idct

[Ian Caulfield]

2008/12/5 Mans Rullgard <mans at mansr.com>:

> +function idct_col4_st8_neon
> +        vshr.s32        q2,  q3,  #COL_SHIFT
> +        vshr.s32        q3,  q4,  #COL_SHIFT
> +        vmovn.i32       d2,  q2
> +        vshr.s32        q4,  q7,  #COL_SHIFT
> +        vmovn.i32       d3,  q3
> +        vshr.s32        q5,  q8,  #COL_SHIFT
> +        vqmovun.s16     d2,  q1
> +        vmovn.i32       d4,  q4
> +        vshr.s32        q6,  q14, #COL_SHIFT
> +        vst1.32         {d2[0]}, [r0,:32], r1
> +        vmovn.i32       d5,  q5
> +        vshr.s32        q7,  q13, #COL_SHIFT
> +        vst1.32         {d2[1]}, [r0,:32], r1
> +        vmovn.i32       d6,  q6
> +        vqmovun.s16     d3,  q2

I'm probably missing something fundamental here, but could the
sequence of instructions

vadd.i32        q3,  q11, q9 (in col4_neon)
vadd.i32        q4,  q12, q10 (in col4_neon)
vshr.s32        q2,  q3,  #COL_SHIFT
vshr.s32        q3,  q4,  #COL_SHIFT
vmovn.i32       d2,  q2
vmovn.i32       d3,  q3
vqmovun.s16     d2,  q1

be replaced by something like

vaddhn.s32    d6,  q11, q9
vaddhn.s32    d7,  q12,q10
vqshrun.s16  d2, q3, #COL_SHIFT-16

?

Ian