x86/vf_blend: Add SSE2 optimization for screen

10x faster than C.

Reviewed-by: Paul B Mahol <onemda@gmail.com>

libavfilter/x86/vf_blend.asm

@@ -111,6 +111,13 @@ BLEND_END
     psrlw           %1, 8                ; 00xx00xx  a * b / 255
 %endmacro
 
+%macro SCREEN 4   ; a, b, pw_1, pw_255
+    pxor            %1, %4               ; 00xx00xx  255 - a
+    pxor            %2, %4
+    MULTIPLY        %1, %2, %3
+    pxor            %1, %4               ; 00xx00xx  255 - x / 255
+%endmacro
+
 BLEND_INIT multiply, 4
     pxor       m2, m2
     mova       m3, [pw_1]
@@ -134,6 +141,28 @@ BLEND_INIT multiply, 4
     jl .loop
 BLEND_END
 
+BLEND_INIT screen, 5
+    pxor       m2, m2
+    mova       m3, [pw_1]
+    mova       m4, [pw_255]
+.nextrow:
+    mov        xq, widthq
+
+    .loop:
+        movh            m0, [topq + xq]      ; 0000xxxx
+        movh            m1, [bottomq + xq]
+        punpcklbw       m0, m2               ; 00xx00xx
+        punpcklbw       m1, m2
+
+        SCREEN          m0, m1, m3, m4
+
+        packuswb        m0, m0               ; 0000xxxx
+        movh   [dstq + xq], m0
+        add             xq, mmsize / 2
+
+    jl .loop
+BLEND_END
+
 BLEND_INIT average, 3
     pxor       m2, m2
 .nextrow:

libavfilter/x86/vf_blend_init.c

@@ -37,6 +37,7 @@ BLEND_FUNC(and, sse2)
 BLEND_FUNC(darken, sse2)
 BLEND_FUNC(difference128, sse2)
 BLEND_FUNC(multiply, sse2)
+BLEND_FUNC(screen, sse2)
 BLEND_FUNC(hardmix, sse2)
 BLEND_FUNC(lighten, sse2)
 BLEND_FUNC(or, sse2)
@@ -65,6 +66,7 @@ av_cold void ff_blend_init_x86(FilterParams *param, int is_16bit)
         case BLEND_MULTIPLY: param->blend = ff_blend_multiply_sse2; break;
         case BLEND_OR:       param->blend = ff_blend_or_sse2;       break;
         case BLEND_PHOENIX:  param->blend = ff_blend_phoenix_sse2;  break;
+        case BLEND_SCREEN:   param->blend = ff_blend_screen_sse2; break;
         case BLEND_SUBTRACT: param->blend = ff_blend_subtract_sse2; break;
         case BLEND_XOR:      param->blend = ff_blend_xor_sse2;      break;
         case BLEND_DIFFERENCE: param->blend = ff_blend_difference_sse2; break;