ref: 5cba6516aa020e420106d276bf2dbebc6b517e3f
dir: /vp8/common/arm/armv6/vp8_variance8x8_armv6.asm/
;
; 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_variance8x8_armv6|
ARM
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_variance8x8_armv6| PROC
push {r4-r10, lr}
pld [r0, r1, lsl #0]
pld [r2, r3, lsl #0]
mov r12, #8 ; set loop counter to 8 (=block height)
mov r4, #0 ; initialize sum = 0
mov r5, #0 ; initialize sse = 0
loop
; 1st 4 pixels
ldr r6, [r0, #0x0] ; load 4 src pixels
ldr r7, [r2, #0x0] ; load 4 ref pixels
mov lr, #0 ; constant zero
usub8 r8, r6, r7 ; calculate difference
pld [r0, r1, lsl #1]
sel r10, r8, lr ; select bytes with positive difference
usub8 r9, r7, r6 ; calculate difference with reversed operands
pld [r2, r3, lsl #1]
sel r8, r9, lr ; select bytes with negative difference
; calculate partial sums
usad8 r6, r10, lr ; calculate sum of positive differences
usad8 r7, r8, lr ; calculate sum of negative differences
orr r8, r8, r10 ; differences of all 4 pixels
; calculate total sum
add r4, r4, r6 ; add positive differences to sum
sub r4, r4, r7 ; subtract negative differences from sum
; calculate sse
uxtb16 r7, r8 ; byte (two pixels) to halfwords
uxtb16 r10, r8, ror #8 ; another two pixels to halfwords
smlad r5, r7, r7, r5 ; dual signed multiply, add and accumulate (1)
; 2nd 4 pixels
ldr r6, [r0, #0x4] ; load 4 src pixels
ldr r7, [r2, #0x4] ; load 4 ref pixels
smlad r5, r10, r10, r5 ; dual signed multiply, add and accumulate (2)
usub8 r8, r6, r7 ; calculate difference
add r0, r0, r1 ; set src_ptr to next row
sel r10, r8, lr ; select bytes with positive difference
usub8 r9, r7, r6 ; calculate difference with reversed operands
add r2, r2, r3 ; set dst_ptr to next row
sel r8, r9, lr ; select bytes with negative difference
; calculate partial sums
usad8 r6, r10, lr ; calculate sum of positive differences
usad8 r7, r8, lr ; calculate sum of negative differences
orr r8, r8, r10 ; differences of all 4 pixels
; calculate total sum
add r4, r4, r6 ; add positive differences to sum
sub r4, r4, r7 ; subtract negative differences from sum
; calculate sse
uxtb16 r7, r8 ; byte (two pixels) to halfwords
uxtb16 r10, r8, ror #8 ; another two pixels to halfwords
smlad r5, r7, r7, r5 ; dual signed multiply, add and accumulate (1)
subs r12, r12, #1 ; next row
smlad r5, r10, r10, r5 ; dual signed multiply, add and accumulate (2)
bne loop
; return stuff
ldr r8, [sp, #32] ; get address of sse
mul r1, r4, r4 ; sum * sum
str r5, [r8] ; store sse
sub r0, r5, r1, ASR #6 ; return (sse - ((sum * sum) >> 6))
pop {r4-r10, pc}
ENDP
END