x86/vf_blend: Add SSE2 optimization for divide

4.5x faster than C float version with autovectorization
10  x faster than C int version
25  x faster than C float version without autovectorization

libavfilter/x86/vf_blend.asm

@@ -24,6 +24,7 @@
 
 SECTION_RODATA
 
+ps_255: times 4 dd 255.0
 pw_1:   times 8 dw 1
 pw_128: times 8 dw 128
 pw_255: times 8 dw 255
@@ -218,6 +219,35 @@ BLEND_INIT hardmix, 5
     jl .loop
 BLEND_END
 
+BLEND_INIT divide, 4
+    pxor       m2, m2
+    mova       m3, [ps_255]
+.nextrow:
+    mov        xq, widthq
+
+    .loop:
+        movd            m0, [topq + xq]      ; 000000xx
+        movd            m1, [bottomq + xq]
+        punpcklbw       m0, m2               ; 00000x0x
+        punpcklbw       m1, m2
+        punpcklwd       m0, m2               ; 000x000x
+        punpcklwd       m1, m2
+
+        cvtdq2ps        m0, m0
+        cvtdq2ps        m1, m1
+        divps           m0, m1               ; a / b
+        mulps           m0, m3               ; a / b * 255
+        minps           m0, m3
+        cvttps2dq       m0, m0
+
+        packssdw        m0, m0               ; 00000x0x
+        packuswb        m0, m0               ; 000000xx
+        movd   [dstq + xq], m0
+        add             xq, mmsize / 4
+
+    jl .loop
+BLEND_END
+
 BLEND_INIT phoenix, 4
     mova       m3, [pb_255]
 .nextrow:

libavfilter/x86/vf_blend_init.c

@@ -39,6 +39,7 @@ BLEND_FUNC(difference128, sse2)
 BLEND_FUNC(multiply, sse2)
 BLEND_FUNC(screen, sse2)
 BLEND_FUNC(hardmix, sse2)
+BLEND_FUNC(divide, sse2)
 BLEND_FUNC(lighten, sse2)
 BLEND_FUNC(or, sse2)
 BLEND_FUNC(phoenix, sse2)
@@ -61,6 +62,7 @@ av_cold void ff_blend_init_x86(FilterParams *param, int is_16bit)
         case BLEND_AVERAGE:  param->blend = ff_blend_average_sse2;  break;
         case BLEND_DARKEN:   param->blend = ff_blend_darken_sse2;   break;
         case BLEND_DIFFERENCE128: param->blend = ff_blend_difference128_sse2; break;
+        case BLEND_DIVIDE:   param->blend = ff_blend_divide_sse2;   break;
         case BLEND_HARDMIX:  param->blend = ff_blend_hardmix_sse2;  break;
         case BLEND_LIGHTEN:  param->blend = ff_blend_lighten_sse2;  break;
         case BLEND_MULTIPLY: param->blend = ff_blend_multiply_sse2; break;