lavc/aarch64: Add neon implementation for vsad_intra16

Provide optimized implementation for vsad_intra16 function for arm64.

Performance comparison tests are shown below.
- vsad_4_c: 177.5
- vsad_4_neon: 23.5

Benchmarks and tests are run with checkasm tool on AWS Gravtion 3.
Signed-off-by: Hubert Mazur <hum@semihalf.com>
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/aarch64/me_cmp_init_aarch64.c

@@ -43,6 +43,8 @@ int sse4_neon(MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
 
 int vsad16_neon(MpegEncContext *c, const uint8_t *s1, const uint8_t *s2,
                 ptrdiff_t stride, int h);
+int vsad_intra16_neon(MpegEncContext *c, const uint8_t *s, const uint8_t *dummy,
+                      ptrdiff_t stride, int h) ;
 int vsse16_neon(MpegEncContext *c, const uint8_t *s1, const uint8_t *s2,
                 ptrdiff_t stride, int h);
 
@@ -64,6 +66,7 @@ av_cold void ff_me_cmp_init_aarch64(MECmpContext *c, AVCodecContext *avctx)
         c->sse[2] = sse4_neon;
 
         c->vsad[0] = vsad16_neon;
+        c->vsad[4] = vsad_intra16_neon;
 
         c->vsse[0] = vsse16_neon;
     }

libavcodec/aarch64/me_cmp_neon.S

@@ -736,3 +736,51 @@ function vsse16_neon, export=1
 
         ret
 endfunc
+
+function vsad_intra16_neon, export=1
+        // x0           unused
+        // x1           uint8_t *pix1
+        // x2           uint8_t *dummy
+        // x3           ptrdiff_t stride
+        // w4           int h
+
+        ld1             {v0.16b}, [x1], x3
+        sub             w4, w4, #1 // we need to make h-1 iterations
+        cmp             w4, #3
+        movi            v16.8h, #0
+        b.lt            2f
+
+// make 4 iterations at once
+1:
+        // v = abs( pix1[0] - pix1[0 + stride] )
+        // score = sum(v)
+        ld1             {v1.16b}, [x1], x3
+        ld1             {v2.16b}, [x1], x3
+        uabal           v16.8h, v0.8b, v1.8b
+        ld1             {v3.16b}, [x1], x3
+        uabal2          v16.8h, v0.16b, v1.16b
+        sub             w4, w4, #3
+        uabal           v16.8h, v1.8b, v2.8b
+        cmp             w4, #3
+        uabal2          v16.8h, v1.16b, v2.16b
+        mov             v0.16b, v3.16b
+        uabal           v16.8h, v2.8b, v3.8b
+        uabal2          v16.8h, v2.16b, v3.16b
+        b.ge            1b
+        cbz             w4, 3f
+
+// iterate by one
+2:
+        ld1             {v1.16b}, [x1], x3
+        subs            w4, w4, #1
+        uabal           v16.8h, v0.8b, v1.8b
+        uabal2          v16.8h, v0.16b, v1.16b
+        mov             v0.16b, v1.16b
+        cbnz            w4, 2b
+
+3:
+        uaddlv          s17, v16.8h
+        fmov            w0, s17
+
+        ret
+endfunc