Half pixel variance further optimized for ARMv6

Half pixel interpolations optimized in variance calculations. Separate
function calls to vp8_filter_block2d_bil_x_pass_armv6 are avoided.On
average, performance improvement is 6-7% for VGA@30fps sequences.

Change-Id: Idb5f118a9d51548e824719d2cfe5be0fa6996628

4 files changed, 582 insertions, 11 deletions

diff --git a/vp8/encoder/arm/armv6/vp8_variance16x16_armv6.asm b/vp8/encoder/arm/armv6/vp8_variance16x16_armv6.asm
index 8d7258af7..988376390 100644
--- a/vp8/encoder/arm/armv6/vp8_variance16x16_armv6.asm
+++ b/vp8/encoder/arm/armv6/vp8_variance16x16_armv6.asm
@@ -25,14 +25,14 @@
 |vp8_variance16x16_armv6| PROC
 
     stmfd   sp!, {r4-r12, lr}
-    mov     r12, #16            ; set loop counter to 16 (=block height)
     mov     r8, #0              ; initialize sum = 0
     mov     r11, #0             ; initialize sse = 0
+    mov     r12, #16            ; set loop counter to 16 (=block height)
 
 loop
     ; 1st 4 pixels
-    ldr     r4, [r0, #0x0]      ; load 4 src pixels
-    ldr     r5, [r2, #0x0]      ; load 4 ref pixels
+    ldr     r4, [r0, #0]        ; load 4 src pixels
+    ldr     r5, [r2, #0]        ; load 4 ref pixels
 
     mov     lr, #0              ; constant zero
 
@@ -55,8 +55,8 @@ loop
     smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
 
     ; 2nd 4 pixels
-    ldr     r4, [r0, #0x4]      ; load 4 src pixels
-    ldr     r5, [r2, #0x4]      ; load 4 ref pixels
+    ldr     r4, [r0, #4]        ; load 4 src pixels
+    ldr     r5, [r2, #4]        ; load 4 ref pixels
     smlad   r11, r10, r10, r11  ; dual signed multiply, add and accumulate (2)
 
     usub8   r6, r4, r5          ; calculate difference
@@ -79,8 +79,8 @@ loop
     smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
 
     ; 3rd 4 pixels
-    ldr     r4, [r0, #0x8]      ; load 4 src pixels
-    ldr     r5, [r2, #0x8]      ; load 4 ref pixels
+    ldr     r4, [r0, #8]        ; load 4 src pixels
+    ldr     r5, [r2, #8]        ; load 4 ref pixels
     smlad   r11, r10, r10, r11  ; dual signed multiply, add and accumulate (2)
 
     usub8   r6, r4, r5          ; calculate difference
@@ -103,8 +103,8 @@ loop
     smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
 
     ; 4th 4 pixels
-    ldr     r4, [r0, #0xc]      ; load 4 src pixels
-    ldr     r5, [r2, #0xc]      ; load 4 ref pixels
+    ldr     r4, [r0, #12]       ; load 4 src pixels
+    ldr     r5, [r2, #12]       ; load 4 ref pixels
     smlad   r11, r10, r10, r11  ; dual signed multiply, add and accumulate (2)
 
     usub8   r6, r4, r5          ; calculate difference
@@ -135,13 +135,14 @@ loop
     bne     loop
 
     ; return stuff
-    ldr     r6, [sp, #0x28]     ; get address of sse
+    ldr     r6, [sp, #40]       ; get address of sse
     mul     r0, r8, r8          ; sum * sum
     str     r11, [r6]           ; store sse
-    sub     r0, r11, r0, ASR #8 ; return (sse - ((sum * sum) >> 8))
+    sub     r0, r11, r0, asr #8 ; return (sse - ((sum * sum) >> 8))
 
     ldmfd   sp!, {r4-r12, pc}
 
     ENDP
 
     END
+
diff --git a/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_h_armv6.asm b/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_h_armv6.asm
new file mode 100644
index 000000000..2350f3e8b
--- /dev/null
+++ b/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_h_armv6.asm
@@ -0,0 +1,176 @@
+;
+;  Copyright (c) 2011 The WebM project authors. All Rights Reserved.
+;
+;  Use of this source code is governed by a BSD-style license
+;  that can be found in the LICENSE file in the root of the source
+;  tree. An additional intellectual property rights grant can be found
+;  in the file PATENTS.  All contributing project authors may
+;  be found in the AUTHORS file in the root of the source tree.
+;
+
+
+    EXPORT  |vp8_variance_halfpixvar16x16_h_armv6|
+
+    ARM
+    REQUIRE8
+    PRESERVE8
+
+    AREA ||.text||, CODE, READONLY, ALIGN=2
+
+; r0    unsigned char *src_ptr
+; r1    int source_stride
+; r2    unsigned char *ref_ptr
+; r3    int  recon_stride
+; stack unsigned int *sse
+|vp8_variance_halfpixvar16x16_h_armv6| PROC
+
+    stmfd   sp!, {r4-r12, lr}
+    mov     r8, #0              ; initialize sum = 0
+    ldr     r10, c80808080
+    mov     r11, #0             ; initialize sse = 0
+    mov     r12, #16            ; set loop counter to 16 (=block height)
+    mov     lr, #0              ; constant zero
+loop
+    ; 1st 4 pixels
+    ldr     r4, [r0, #0]        ; load 4 src pixels
+    ldr     r6, [r0, #1]        ; load 4 src pixels with 1 byte offset
+    ldr     r5, [r2, #0]        ; load 4 ref pixels
+
+    ; bilinear interpolation
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+    ; calculate total sum
+    adds    r8, r8, r4          ; add positive differences to sum
+    subs    r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 2nd 4 pixels
+    ldr     r4, [r0, #4]        ; load 4 src pixels
+    ldr     r6, [r0, #5]        ; load 4 src pixels with 1 byte offset
+    ldr     r5, [r2, #4]        ; load 4 ref pixels
+
+    ; bilinear interpolation
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 3rd 4 pixels
+    ldr     r4, [r0, #8]        ; load 4 src pixels
+    ldr     r6, [r0, #9]        ; load 4 src pixels with 1 byte offset
+    ldr     r5, [r2, #8]        ; load 4 ref pixels
+
+    ; bilinear interpolation
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+
+    smlad   r11, r7, r7, r11  ; dual signed multiply, add and accumulate (2)
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 4th 4 pixels
+    ldr     r4, [r0, #12]       ; load 4 src pixels
+    ldr     r6, [r0, #13]       ; load 4 src pixels with 1 byte offset
+    ldr     r5, [r2, #12]       ; load 4 ref pixels
+
+    ; bilinear interpolation
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    usub8   r6, r4, r5          ; calculate difference
+    add     r0, r0, r1          ; set src_ptr to next row
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    add     r2, r2, r3          ; set dst_ptr to next row
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    subs    r12, r12, #1
+
+    bne     loop
+
+    ; return stuff
+    ldr     r6, [sp, #40]       ; get address of sse
+    mul     r0, r8, r8          ; sum * sum
+    str     r11, [r6]           ; store sse
+    sub     r0, r11, r0, asr #8 ; return (sse - ((sum * sum) >> 8))
+
+    ldmfd   sp!, {r4-r12, pc}
+
+    ENDP
+
+c80808080
+    DCD     0x80808080
+
+    END
+
diff --git a/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_hv_armv6.asm b/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_hv_armv6.asm
new file mode 100644
index 000000000..f9ae3b7e2
--- /dev/null
+++ b/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_hv_armv6.asm
@@ -0,0 +1,216 @@
+;
+;  Copyright (c) 2011 The WebM project authors. All Rights Reserved.
+;
+;  Use of this source code is governed by a BSD-style license
+;  that can be found in the LICENSE file in the root of the source
+;  tree. An additional intellectual property rights grant can be found
+;  in the file PATENTS.  All contributing project authors may
+;  be found in the AUTHORS file in the root of the source tree.
+;
+
+
+    EXPORT  |vp8_variance_halfpixvar16x16_hv_armv6|
+
+    ARM
+    REQUIRE8
+    PRESERVE8
+
+    AREA ||.text||, CODE, READONLY, ALIGN=2
+
+; r0    unsigned char *src_ptr
+; r1    int source_stride
+; r2    unsigned char *ref_ptr
+; r3    int  recon_stride
+; stack unsigned int *sse
+|vp8_variance_halfpixvar16x16_hv_armv6| PROC
+
+    stmfd   sp!, {r4-r12, lr}
+    mov     r8, #0              ; initialize sum = 0
+    ldr     r10, c80808080
+    mov     r11, #0             ; initialize sse = 0
+    mov     r12, #16            ; set loop counter to 16 (=block height)
+    mov     lr, #0              ; constant zero
+loop
+    add     r9, r0, r1          ; pointer to pixels on the next row
+    ; 1st 4 pixels
+    ldr     r4, [r0, #0]        ; load source pixels a, row N
+    ldr     r6, [r0, #1]        ; load source pixels b, row N
+    ldr     r5, [r9, #0]        ; load source pixels c, row N+1
+    ldr     r7, [r9, #1]        ; load source pixels d, row N+1
+
+    ; x = (a + b + 1) >> 1, interpolate pixels horizontally on row N
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+    ; y = (c + d + 1) >> 1, interpolate pixels horizontally on row N+1
+    mvn     r7, r7
+    uhsub8  r5, r5, r7
+    eor     r5, r5, r10
+    ; z = (x + y + 1) >> 1, interpolate half pixel values vertically
+    mvn     r5, r5
+    uhsub8  r4, r4, r5
+    ldr     r5, [r2, #0]        ; load 4 ref pixels
+    eor     r4, r4, r10
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+    ; calculate total sum
+    adds    r8, r8, r4          ; add positive differences to sum
+    subs    r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 2nd 4 pixels
+    ldr     r4, [r0, #4]        ; load source pixels a, row N
+    ldr     r6, [r0, #5]        ; load source pixels b, row N
+    ldr     r5, [r9, #4]        ; load source pixels c, row N+1
+
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    ldr     r7, [r9, #5]        ; load source pixels d, row N+1
+
+    ; x = (a + b + 1) >> 1, interpolate pixels horizontally on row N
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+    ; y = (c + d + 1) >> 1, interpolate pixels horizontally on row N+1
+    mvn     r7, r7
+    uhsub8  r5, r5, r7
+    eor     r5, r5, r10
+    ; z = (x + y + 1) >> 1, interpolate half pixel values vertically
+    mvn     r5, r5
+    uhsub8  r4, r4, r5
+    ldr     r5, [r2, #4]        ; load 4 ref pixels
+    eor     r4, r4, r10
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 3rd 4 pixels
+    ldr     r4, [r0, #8]        ; load source pixels a, row N
+    ldr     r6, [r0, #9]        ; load source pixels b, row N
+    ldr     r5, [r9, #8]        ; load source pixels c, row N+1
+
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    ldr     r7, [r9, #9]        ; load source pixels d, row N+1
+
+    ; x = (a + b + 1) >> 1, interpolate pixels horizontally on row N
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+    ; y = (c + d + 1) >> 1, interpolate pixels horizontally on row N+1
+    mvn     r7, r7
+    uhsub8  r5, r5, r7
+    eor     r5, r5, r10
+    ; z = (x + y + 1) >> 1, interpolate half pixel values vertically
+    mvn     r5, r5
+    uhsub8  r4, r4, r5
+    ldr     r5, [r2, #8]        ; load 4 ref pixels
+    eor     r4, r4, r10
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 4th 4 pixels
+    ldr     r4, [r0, #12]       ; load source pixels a, row N
+    ldr     r6, [r0, #13]       ; load source pixels b, row N
+    ldr     r5, [r9, #12]       ; load source pixels c, row N+1
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+    ldr     r7, [r9, #13]       ; load source pixels d, row N+1
+
+    ; x = (a + b + 1) >> 1, interpolate pixels horizontally on row N
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+    ; y = (c + d + 1) >> 1, interpolate pixels horizontally on row N+1
+    mvn     r7, r7
+    uhsub8  r5, r5, r7
+    eor     r5, r5, r10
+    ; z = (x + y + 1) >> 1, interpolate half pixel values vertically
+    mvn     r5, r5
+    uhsub8  r4, r4, r5
+    ldr     r5, [r2, #12]       ; load 4 ref pixels
+    eor     r4, r4, r10
+
+    usub8   r6, r4, r5          ; calculate difference
+    add     r0, r0, r1          ; set src_ptr to next row
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    add     r2, r2, r3          ; set dst_ptr to next row
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+    subs    r12, r12, #1
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    bne     loop
+
+    ; return stuff
+    ldr     r6, [sp, #40]       ; get address of sse
+    mul     r0, r8, r8          ; sum * sum
+    str     r11, [r6]           ; store sse
+    sub     r0, r11, r0, asr #8 ; return (sse - ((sum * sum) >> 8))
+
+    ldmfd   sp!, {r4-r12, pc}
+
+    ENDP
+
+c80808080
+    DCD     0x80808080
+
+    END
diff --git a/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_v_armv6.asm b/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_v_armv6.asm
new file mode 100644
index 000000000..9e0a03548
--- /dev/null
+++ b/vp8/encoder/arm/armv6/vp8_variance_halfpixvar16x16_v_armv6.asm
@@ -0,0 +1,178 @@
+;
+;  Copyright (c) 2011 The WebM project authors. All Rights Reserved.
+;
+;  Use of this source code is governed by a BSD-style license
+;  that can be found in the LICENSE file in the root of the source
+;  tree. An additional intellectual property rights grant can be found
+;  in the file PATENTS.  All contributing project authors may
+;  be found in the AUTHORS file in the root of the source tree.
+;
+
+
+    EXPORT  |vp8_variance_halfpixvar16x16_v_armv6|
+
+    ARM
+    REQUIRE8
+    PRESERVE8
+
+    AREA ||.text||, CODE, READONLY, ALIGN=2
+
+; r0    unsigned char *src_ptr
+; r1    int source_stride
+; r2    unsigned char *ref_ptr
+; r3    int  recon_stride
+; stack unsigned int *sse
+|vp8_variance_halfpixvar16x16_v_armv6| PROC
+
+    stmfd   sp!, {r4-r12, lr}
+    mov     r8, #0              ; initialize sum = 0
+    ldr     r10, c80808080
+    mov     r11, #0             ; initialize sse = 0
+    mov     r12, #16            ; set loop counter to 16 (=block height)
+    mov     lr, #0              ; constant zero
+loop
+    add     r9, r0, r1          ; set src pointer to next row
+    ; 1st 4 pixels
+    ldr     r4, [r0, #0]        ; load 4 src pixels
+    ldr     r6, [r9, #0]        ; load 4 src pixels from next row
+    ldr     r5, [r2, #0]        ; load 4 ref pixels
+
+    ; bilinear interpolation
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+    ; calculate total sum
+    adds    r8, r8, r4          ; add positive differences to sum
+    subs    r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 2nd 4 pixels
+    ldr     r4, [r0, #4]        ; load 4 src pixels
+    ldr     r6, [r9, #4]        ; load 4 src pixels from next row
+    ldr     r5, [r2, #4]        ; load 4 ref pixels
+
+    ; bilinear interpolation
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 3rd 4 pixels
+    ldr     r4, [r0, #8]        ; load 4 src pixels
+    ldr     r6, [r9, #8]        ; load 4 src pixels from next row
+    ldr     r5, [r2, #8]        ; load 4 ref pixels
+
+    ; bilinear interpolation
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    usub8   r6, r4, r5          ; calculate difference
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+
+    ; 4th 4 pixels
+    ldr     r4, [r0, #12]       ; load 4 src pixels
+    ldr     r6, [r9, #12]       ; load 4 src pixels from next row
+    ldr     r5, [r2, #12]       ; load 4 ref pixels
+
+    ; bilinear interpolation
+    mvn     r6, r6
+    uhsub8  r4, r4, r6
+    eor     r4, r4, r10
+
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+    usub8   r6, r4, r5          ; calculate difference
+    add     r0, r0, r1          ; set src_ptr to next row
+    sel     r7, r6, lr          ; select bytes with positive difference
+    usub8   r6, r5, r4          ; calculate difference with reversed operands
+    add     r2, r2, r3          ; set dst_ptr to next row
+    sel     r6, r6, lr          ; select bytes with negative difference
+
+    ; calculate partial sums
+    usad8   r4, r7, lr          ; calculate sum of positive differences
+    usad8   r5, r6, lr          ; calculate sum of negative differences
+    orr     r6, r6, r7          ; differences of all 4 pixels
+
+    ; calculate total sum
+    add     r8, r8, r4          ; add positive differences to sum
+    sub     r8, r8, r5          ; substract negative differences from sum
+
+    ; calculate sse
+    uxtb16  r5, r6              ; byte (two pixels) to halfwords
+    uxtb16  r7, r6, ror #8      ; another two pixels to halfwords
+    smlad   r11, r5, r5, r11    ; dual signed multiply, add and accumulate (1)
+    smlad   r11, r7, r7, r11    ; dual signed multiply, add and accumulate (2)
+
+
+    subs    r12, r12, #1
+
+    bne     loop
+
+    ; return stuff
+    ldr     r6, [sp, #40]       ; get address of sse
+    mul     r0, r8, r8          ; sum * sum
+    str     r11, [r6]           ; store sse
+    sub     r0, r11, r0, asr #8 ; return (sse - ((sum * sum) >> 8))
+
+    ldmfd   sp!, {r4-r12, pc}
+
+    ENDP
+
+c80808080
+    DCD     0x80808080
+
+    END
+