libvpx: Add VP9 decoder.

source/libvpx/vp9/encoder/ppc/vp9_rdopt_altivec.asm

+;
+;  Copyright (c) 2010 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.
+;
+
+
+    .globl vp8_block_error_ppc
+
+    .align 2
+;# r3 short *Coeff
+;# r4 short *dqcoeff
+vp8_block_error_ppc:
+    mfspr   r11, 256            ;# get old VRSAVE
+    oris    r12, r11, 0xf800
+    mtspr   256, r12            ;# set VRSAVE
+
+    stwu    r1,-32(r1)          ;# create space on the stack
+
+    stw     r5, 12(r1)          ;# tranfer dc to vector register
+
+    lvx     v0, 0, r3           ;# Coeff
+    lvx     v1, 0, r4           ;# dqcoeff
+
+    li      r10, 16
+
+    vspltisw v3, 0
+
+    vsubshs v0, v0, v1
+
+    vmsumshm v2, v0, v0, v3     ;# multiply differences
+
+    lvx     v0, r10, r3         ;# Coeff
+    lvx     v1, r10, r4         ;# dqcoeff
+
+    vsubshs v0, v0, v1
+
+    vmsumshm v1, v0, v0, v2     ;# multiply differences
+    vsumsws v1, v1, v3          ;# sum up
+
+    stvx    v1, 0, r1
+    lwz     r3, 12(r1)          ;# return value
+
+    addi    r1, r1, 32          ;# recover stack
+    mtspr   256, r11            ;# reset old VRSAVE
+
+    blr