summaryrefslogtreecommitdiffstats
path: root/media/libwebp/dec/vp8_dec.c
diff options
context:
space:
mode:
authorwolfbeast <mcwerewolf@gmail.com>2017-07-24 13:19:25 +0200
committerwolfbeast <mcwerewolf@gmail.com>2018-02-03 09:57:42 +0100
commit2c1f833a092ef7af17f072749940bcb47da19aa6 (patch)
treee1904491a9c9a745d77df2225b679d921156affc /media/libwebp/dec/vp8_dec.c
parentc0cfd6f89cd6b25cc8aaea1a1eb7bc004c88c206 (diff)
downloadUXP-2c1f833a092ef7af17f072749940bcb47da19aa6.tar
UXP-2c1f833a092ef7af17f072749940bcb47da19aa6.tar.gz
UXP-2c1f833a092ef7af17f072749940bcb47da19aa6.tar.lz
UXP-2c1f833a092ef7af17f072749940bcb47da19aa6.tar.xz
UXP-2c1f833a092ef7af17f072749940bcb47da19aa6.zip
Add libwebp 0.6.0 to the tree
Diffstat (limited to 'media/libwebp/dec/vp8_dec.c')
-rw-r--r--media/libwebp/dec/vp8_dec.c721
1 files changed, 721 insertions, 0 deletions
diff --git a/media/libwebp/dec/vp8_dec.c b/media/libwebp/dec/vp8_dec.c
new file mode 100644
index 000000000..fad8d9cf3
--- /dev/null
+++ b/media/libwebp/dec/vp8_dec.c
@@ -0,0 +1,721 @@
+// Copyright 2010 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING 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.
+// -----------------------------------------------------------------------------
+//
+// main entry for the decoder
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#include <stdlib.h>
+
+#include "./alphai_dec.h"
+#include "./vp8i_dec.h"
+#include "./vp8li_dec.h"
+#include "./webpi_dec.h"
+#include "../utils/bit_reader_inl_utils.h"
+#include "../utils/utils.h"
+
+//------------------------------------------------------------------------------
+
+int WebPGetDecoderVersion(void) {
+ return (DEC_MAJ_VERSION << 16) | (DEC_MIN_VERSION << 8) | DEC_REV_VERSION;
+}
+
+//------------------------------------------------------------------------------
+// Signature and pointer-to-function for GetCoeffs() variants below.
+
+typedef int (*GetCoeffsFunc)(VP8BitReader* const br,
+ const VP8BandProbas* const prob[],
+ int ctx, const quant_t dq, int n, int16_t* out);
+static volatile GetCoeffsFunc GetCoeffs = NULL;
+
+static void InitGetCoeffs(void);
+
+//------------------------------------------------------------------------------
+// VP8Decoder
+
+static void SetOk(VP8Decoder* const dec) {
+ dec->status_ = VP8_STATUS_OK;
+ dec->error_msg_ = "OK";
+}
+
+int VP8InitIoInternal(VP8Io* const io, int version) {
+ if (WEBP_ABI_IS_INCOMPATIBLE(version, WEBP_DECODER_ABI_VERSION)) {
+ return 0; // mismatch error
+ }
+ if (io != NULL) {
+ memset(io, 0, sizeof(*io));
+ }
+ return 1;
+}
+
+VP8Decoder* VP8New(void) {
+ VP8Decoder* const dec = (VP8Decoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
+ if (dec != NULL) {
+ SetOk(dec);
+ WebPGetWorkerInterface()->Init(&dec->worker_);
+ dec->ready_ = 0;
+ dec->num_parts_minus_one_ = 0;
+ InitGetCoeffs();
+ }
+ return dec;
+}
+
+VP8StatusCode VP8Status(VP8Decoder* const dec) {
+ if (!dec) return VP8_STATUS_INVALID_PARAM;
+ return dec->status_;
+}
+
+const char* VP8StatusMessage(VP8Decoder* const dec) {
+ if (dec == NULL) return "no object";
+ if (!dec->error_msg_) return "OK";
+ return dec->error_msg_;
+}
+
+void VP8Delete(VP8Decoder* const dec) {
+ if (dec != NULL) {
+ VP8Clear(dec);
+ WebPSafeFree(dec);
+ }
+}
+
+int VP8SetError(VP8Decoder* const dec,
+ VP8StatusCode error, const char* const msg) {
+ // The oldest error reported takes precedence over the new one.
+ if (dec->status_ == VP8_STATUS_OK) {
+ dec->status_ = error;
+ dec->error_msg_ = msg;
+ dec->ready_ = 0;
+ }
+ return 0;
+}
+
+//------------------------------------------------------------------------------
+
+int VP8CheckSignature(const uint8_t* const data, size_t data_size) {
+ return (data_size >= 3 &&
+ data[0] == 0x9d && data[1] == 0x01 && data[2] == 0x2a);
+}
+
+int VP8GetInfo(const uint8_t* data, size_t data_size, size_t chunk_size,
+ int* const width, int* const height) {
+ if (data == NULL || data_size < VP8_FRAME_HEADER_SIZE) {
+ return 0; // not enough data
+ }
+ // check signature
+ if (!VP8CheckSignature(data + 3, data_size - 3)) {
+ return 0; // Wrong signature.
+ } else {
+ const uint32_t bits = data[0] | (data[1] << 8) | (data[2] << 16);
+ const int key_frame = !(bits & 1);
+ const int w = ((data[7] << 8) | data[6]) & 0x3fff;
+ const int h = ((data[9] << 8) | data[8]) & 0x3fff;
+
+ if (!key_frame) { // Not a keyframe.
+ return 0;
+ }
+
+ if (((bits >> 1) & 7) > 3) {
+ return 0; // unknown profile
+ }
+ if (!((bits >> 4) & 1)) {
+ return 0; // first frame is invisible!
+ }
+ if (((bits >> 5)) >= chunk_size) { // partition_length
+ return 0; // inconsistent size information.
+ }
+ if (w == 0 || h == 0) {
+ return 0; // We don't support both width and height to be zero.
+ }
+
+ if (width) {
+ *width = w;
+ }
+ if (height) {
+ *height = h;
+ }
+
+ return 1;
+ }
+}
+
+//------------------------------------------------------------------------------
+// Header parsing
+
+static void ResetSegmentHeader(VP8SegmentHeader* const hdr) {
+ assert(hdr != NULL);
+ hdr->use_segment_ = 0;
+ hdr->update_map_ = 0;
+ hdr->absolute_delta_ = 1;
+ memset(hdr->quantizer_, 0, sizeof(hdr->quantizer_));
+ memset(hdr->filter_strength_, 0, sizeof(hdr->filter_strength_));
+}
+
+// Paragraph 9.3
+static int ParseSegmentHeader(VP8BitReader* br,
+ VP8SegmentHeader* hdr, VP8Proba* proba) {
+ assert(br != NULL);
+ assert(hdr != NULL);
+ hdr->use_segment_ = VP8Get(br);
+ if (hdr->use_segment_) {
+ hdr->update_map_ = VP8Get(br);
+ if (VP8Get(br)) { // update data
+ int s;
+ hdr->absolute_delta_ = VP8Get(br);
+ for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
+ hdr->quantizer_[s] = VP8Get(br) ? VP8GetSignedValue(br, 7) : 0;
+ }
+ for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
+ hdr->filter_strength_[s] = VP8Get(br) ? VP8GetSignedValue(br, 6) : 0;
+ }
+ }
+ if (hdr->update_map_) {
+ int s;
+ for (s = 0; s < MB_FEATURE_TREE_PROBS; ++s) {
+ proba->segments_[s] = VP8Get(br) ? VP8GetValue(br, 8) : 255u;
+ }
+ }
+ } else {
+ hdr->update_map_ = 0;
+ }
+ return !br->eof_;
+}
+
+// Paragraph 9.5
+// This function returns VP8_STATUS_SUSPENDED if we don't have all the
+// necessary data in 'buf'.
+// This case is not necessarily an error (for incremental decoding).
+// Still, no bitreader is ever initialized to make it possible to read
+// unavailable memory.
+// If we don't even have the partitions' sizes, than VP8_STATUS_NOT_ENOUGH_DATA
+// is returned, and this is an unrecoverable error.
+// If the partitions were positioned ok, VP8_STATUS_OK is returned.
+static VP8StatusCode ParsePartitions(VP8Decoder* const dec,
+ const uint8_t* buf, size_t size) {
+ VP8BitReader* const br = &dec->br_;
+ const uint8_t* sz = buf;
+ const uint8_t* buf_end = buf + size;
+ const uint8_t* part_start;
+ size_t size_left = size;
+ size_t last_part;
+ size_t p;
+
+ dec->num_parts_minus_one_ = (1 << VP8GetValue(br, 2)) - 1;
+ last_part = dec->num_parts_minus_one_;
+ if (size < 3 * last_part) {
+ // we can't even read the sizes with sz[]! That's a failure.
+ return VP8_STATUS_NOT_ENOUGH_DATA;
+ }
+ part_start = buf + last_part * 3;
+ size_left -= last_part * 3;
+ for (p = 0; p < last_part; ++p) {
+ size_t psize = sz[0] | (sz[1] << 8) | (sz[2] << 16);
+ if (psize > size_left) psize = size_left;
+ VP8InitBitReader(dec->parts_ + p, part_start, psize);
+ part_start += psize;
+ size_left -= psize;
+ sz += 3;
+ }
+ VP8InitBitReader(dec->parts_ + last_part, part_start, size_left);
+ return (part_start < buf_end) ? VP8_STATUS_OK :
+ VP8_STATUS_SUSPENDED; // Init is ok, but there's not enough data
+}
+
+// Paragraph 9.4
+static int ParseFilterHeader(VP8BitReader* br, VP8Decoder* const dec) {
+ VP8FilterHeader* const hdr = &dec->filter_hdr_;
+ hdr->simple_ = VP8Get(br);
+ hdr->level_ = VP8GetValue(br, 6);
+ hdr->sharpness_ = VP8GetValue(br, 3);
+ hdr->use_lf_delta_ = VP8Get(br);
+ if (hdr->use_lf_delta_) {
+ if (VP8Get(br)) { // update lf-delta?
+ int i;
+ for (i = 0; i < NUM_REF_LF_DELTAS; ++i) {
+ if (VP8Get(br)) {
+ hdr->ref_lf_delta_[i] = VP8GetSignedValue(br, 6);
+ }
+ }
+ for (i = 0; i < NUM_MODE_LF_DELTAS; ++i) {
+ if (VP8Get(br)) {
+ hdr->mode_lf_delta_[i] = VP8GetSignedValue(br, 6);
+ }
+ }
+ }
+ }
+ dec->filter_type_ = (hdr->level_ == 0) ? 0 : hdr->simple_ ? 1 : 2;
+ return !br->eof_;
+}
+
+// Topmost call
+int VP8GetHeaders(VP8Decoder* const dec, VP8Io* const io) {
+ const uint8_t* buf;
+ size_t buf_size;
+ VP8FrameHeader* frm_hdr;
+ VP8PictureHeader* pic_hdr;
+ VP8BitReader* br;
+ VP8StatusCode status;
+
+ if (dec == NULL) {
+ return 0;
+ }
+ SetOk(dec);
+ if (io == NULL) {
+ return VP8SetError(dec, VP8_STATUS_INVALID_PARAM,
+ "null VP8Io passed to VP8GetHeaders()");
+ }
+ buf = io->data;
+ buf_size = io->data_size;
+ if (buf_size < 4) {
+ return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
+ "Truncated header.");
+ }
+
+ // Paragraph 9.1
+ {
+ const uint32_t bits = buf[0] | (buf[1] << 8) | (buf[2] << 16);
+ frm_hdr = &dec->frm_hdr_;
+ frm_hdr->key_frame_ = !(bits & 1);
+ frm_hdr->profile_ = (bits >> 1) & 7;
+ frm_hdr->show_ = (bits >> 4) & 1;
+ frm_hdr->partition_length_ = (bits >> 5);
+ if (frm_hdr->profile_ > 3) {
+ return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
+ "Incorrect keyframe parameters.");
+ }
+ if (!frm_hdr->show_) {
+ return VP8SetError(dec, VP8_STATUS_UNSUPPORTED_FEATURE,
+ "Frame not displayable.");
+ }
+ buf += 3;
+ buf_size -= 3;
+ }
+
+ pic_hdr = &dec->pic_hdr_;
+ if (frm_hdr->key_frame_) {
+ // Paragraph 9.2
+ if (buf_size < 7) {
+ return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
+ "cannot parse picture header");
+ }
+ if (!VP8CheckSignature(buf, buf_size)) {
+ return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
+ "Bad code word");
+ }
+ pic_hdr->width_ = ((buf[4] << 8) | buf[3]) & 0x3fff;
+ pic_hdr->xscale_ = buf[4] >> 6; // ratio: 1, 5/4 5/3 or 2
+ pic_hdr->height_ = ((buf[6] << 8) | buf[5]) & 0x3fff;
+ pic_hdr->yscale_ = buf[6] >> 6;
+ buf += 7;
+ buf_size -= 7;
+
+ dec->mb_w_ = (pic_hdr->width_ + 15) >> 4;
+ dec->mb_h_ = (pic_hdr->height_ + 15) >> 4;
+
+ // Setup default output area (can be later modified during io->setup())
+ io->width = pic_hdr->width_;
+ io->height = pic_hdr->height_;
+ // IMPORTANT! use some sane dimensions in crop_* and scaled_* fields.
+ // So they can be used interchangeably without always testing for
+ // 'use_cropping'.
+ io->use_cropping = 0;
+ io->crop_top = 0;
+ io->crop_left = 0;
+ io->crop_right = io->width;
+ io->crop_bottom = io->height;
+ io->use_scaling = 0;
+ io->scaled_width = io->width;
+ io->scaled_height = io->height;
+
+ io->mb_w = io->width; // sanity check
+ io->mb_h = io->height; // ditto
+
+ VP8ResetProba(&dec->proba_);
+ ResetSegmentHeader(&dec->segment_hdr_);
+ }
+
+ // Check if we have all the partition #0 available, and initialize dec->br_
+ // to read this partition (and this partition only).
+ if (frm_hdr->partition_length_ > buf_size) {
+ return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
+ "bad partition length");
+ }
+
+ br = &dec->br_;
+ VP8InitBitReader(br, buf, frm_hdr->partition_length_);
+ buf += frm_hdr->partition_length_;
+ buf_size -= frm_hdr->partition_length_;
+
+ if (frm_hdr->key_frame_) {
+ pic_hdr->colorspace_ = VP8Get(br);
+ pic_hdr->clamp_type_ = VP8Get(br);
+ }
+ if (!ParseSegmentHeader(br, &dec->segment_hdr_, &dec->proba_)) {
+ return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
+ "cannot parse segment header");
+ }
+ // Filter specs
+ if (!ParseFilterHeader(br, dec)) {
+ return VP8SetError(dec, VP8_STATUS_BITSTREAM_ERROR,
+ "cannot parse filter header");
+ }
+ status = ParsePartitions(dec, buf, buf_size);
+ if (status != VP8_STATUS_OK) {
+ return VP8SetError(dec, status, "cannot parse partitions");
+ }
+
+ // quantizer change
+ VP8ParseQuant(dec);
+
+ // Frame buffer marking
+ if (!frm_hdr->key_frame_) {
+ return VP8SetError(dec, VP8_STATUS_UNSUPPORTED_FEATURE,
+ "Not a key frame.");
+ }
+
+ VP8Get(br); // ignore the value of update_proba_
+
+ VP8ParseProba(br, dec);
+
+ // sanitized state
+ dec->ready_ = 1;
+ return 1;
+}
+
+//------------------------------------------------------------------------------
+// Residual decoding (Paragraph 13.2 / 13.3)
+
+static const uint8_t kCat3[] = { 173, 148, 140, 0 };
+static const uint8_t kCat4[] = { 176, 155, 140, 135, 0 };
+static const uint8_t kCat5[] = { 180, 157, 141, 134, 130, 0 };
+static const uint8_t kCat6[] =
+ { 254, 254, 243, 230, 196, 177, 153, 140, 133, 130, 129, 0 };
+static const uint8_t* const kCat3456[] = { kCat3, kCat4, kCat5, kCat6 };
+static const uint8_t kZigzag[16] = {
+ 0, 1, 4, 8, 5, 2, 3, 6, 9, 12, 13, 10, 7, 11, 14, 15
+};
+
+// See section 13-2: http://tools.ietf.org/html/rfc6386#section-13.2
+static int GetLargeValue(VP8BitReader* const br, const uint8_t* const p) {
+ int v;
+ if (!VP8GetBit(br, p[3])) {
+ if (!VP8GetBit(br, p[4])) {
+ v = 2;
+ } else {
+ v = 3 + VP8GetBit(br, p[5]);
+ }
+ } else {
+ if (!VP8GetBit(br, p[6])) {
+ if (!VP8GetBit(br, p[7])) {
+ v = 5 + VP8GetBit(br, 159);
+ } else {
+ v = 7 + 2 * VP8GetBit(br, 165);
+ v += VP8GetBit(br, 145);
+ }
+ } else {
+ const uint8_t* tab;
+ const int bit1 = VP8GetBit(br, p[8]);
+ const int bit0 = VP8GetBit(br, p[9 + bit1]);
+ const int cat = 2 * bit1 + bit0;
+ v = 0;
+ for (tab = kCat3456[cat]; *tab; ++tab) {
+ v += v + VP8GetBit(br, *tab);
+ }
+ v += 3 + (8 << cat);
+ }
+ }
+ return v;
+}
+
+// Returns the position of the last non-zero coeff plus one
+static int GetCoeffsFast(VP8BitReader* const br,
+ const VP8BandProbas* const prob[],
+ int ctx, const quant_t dq, int n, int16_t* out) {
+ const uint8_t* p = prob[n]->probas_[ctx];
+ for (; n < 16; ++n) {
+ if (!VP8GetBit(br, p[0])) {
+ return n; // previous coeff was last non-zero coeff
+ }
+ while (!VP8GetBit(br, p[1])) { // sequence of zero coeffs
+ p = prob[++n]->probas_[0];
+ if (n == 16) return 16;
+ }
+ { // non zero coeff
+ const VP8ProbaArray* const p_ctx = &prob[n + 1]->probas_[0];
+ int v;
+ if (!VP8GetBit(br, p[2])) {
+ v = 1;
+ p = p_ctx[1];
+ } else {
+ v = GetLargeValue(br, p);
+ p = p_ctx[2];
+ }
+ out[kZigzag[n]] = VP8GetSigned(br, v) * dq[n > 0];
+ }
+ }
+ return 16;
+}
+
+// This version of GetCoeffs() uses VP8GetBitAlt() which is an alternate version
+// of VP8GetBitAlt() targeting specific platforms.
+static int GetCoeffsAlt(VP8BitReader* const br,
+ const VP8BandProbas* const prob[],
+ int ctx, const quant_t dq, int n, int16_t* out) {
+ const uint8_t* p = prob[n]->probas_[ctx];
+ for (; n < 16; ++n) {
+ if (!VP8GetBitAlt(br, p[0])) {
+ return n; // previous coeff was last non-zero coeff
+ }
+ while (!VP8GetBitAlt(br, p[1])) { // sequence of zero coeffs
+ p = prob[++n]->probas_[0];
+ if (n == 16) return 16;
+ }
+ { // non zero coeff
+ const VP8ProbaArray* const p_ctx = &prob[n + 1]->probas_[0];
+ int v;
+ if (!VP8GetBitAlt(br, p[2])) {
+ v = 1;
+ p = p_ctx[1];
+ } else {
+ v = GetLargeValue(br, p);
+ p = p_ctx[2];
+ }
+ out[kZigzag[n]] = VP8GetSigned(br, v) * dq[n > 0];
+ }
+ }
+ return 16;
+}
+
+WEBP_TSAN_IGNORE_FUNCTION static void InitGetCoeffs(void) {
+ if (GetCoeffs == NULL) {
+ if (VP8GetCPUInfo != NULL && VP8GetCPUInfo(kSlowSSSE3)) {
+ GetCoeffs = GetCoeffsAlt;
+ } else {
+ GetCoeffs = GetCoeffsFast;
+ }
+ }
+}
+
+static WEBP_INLINE uint32_t NzCodeBits(uint32_t nz_coeffs, int nz, int dc_nz) {
+ nz_coeffs <<= 2;
+ nz_coeffs |= (nz > 3) ? 3 : (nz > 1) ? 2 : dc_nz;
+ return nz_coeffs;
+}
+
+static int ParseResiduals(VP8Decoder* const dec,
+ VP8MB* const mb, VP8BitReader* const token_br) {
+ const VP8BandProbas* (* const bands)[16 + 1] = dec->proba_.bands_ptr_;
+ const VP8BandProbas* const * ac_proba;
+ VP8MBData* const block = dec->mb_data_ + dec->mb_x_;
+ const VP8QuantMatrix* const q = &dec->dqm_[block->segment_];
+ int16_t* dst = block->coeffs_;
+ VP8MB* const left_mb = dec->mb_info_ - 1;
+ uint8_t tnz, lnz;
+ uint32_t non_zero_y = 0;
+ uint32_t non_zero_uv = 0;
+ int x, y, ch;
+ uint32_t out_t_nz, out_l_nz;
+ int first;
+
+ memset(dst, 0, 384 * sizeof(*dst));
+ if (!block->is_i4x4_) { // parse DC
+ int16_t dc[16] = { 0 };
+ const int ctx = mb->nz_dc_ + left_mb->nz_dc_;
+ const int nz = GetCoeffs(token_br, bands[1], ctx, q->y2_mat_, 0, dc);
+ mb->nz_dc_ = left_mb->nz_dc_ = (nz > 0);
+ if (nz > 1) { // more than just the DC -> perform the full transform
+ VP8TransformWHT(dc, dst);
+ } else { // only DC is non-zero -> inlined simplified transform
+ int i;
+ const int dc0 = (dc[0] + 3) >> 3;
+ for (i = 0; i < 16 * 16; i += 16) dst[i] = dc0;
+ }
+ first = 1;
+ ac_proba = bands[0];
+ } else {
+ first = 0;
+ ac_proba = bands[3];
+ }
+
+ tnz = mb->nz_ & 0x0f;
+ lnz = left_mb->nz_ & 0x0f;
+ for (y = 0; y < 4; ++y) {
+ int l = lnz & 1;
+ uint32_t nz_coeffs = 0;
+ for (x = 0; x < 4; ++x) {
+ const int ctx = l + (tnz & 1);
+ const int nz = GetCoeffs(token_br, ac_proba, ctx, q->y1_mat_, first, dst);
+ l = (nz > first);
+ tnz = (tnz >> 1) | (l << 7);
+ nz_coeffs = NzCodeBits(nz_coeffs, nz, dst[0] != 0);
+ dst += 16;
+ }
+ tnz >>= 4;
+ lnz = (lnz >> 1) | (l << 7);
+ non_zero_y = (non_zero_y << 8) | nz_coeffs;
+ }
+ out_t_nz = tnz;
+ out_l_nz = lnz >> 4;
+
+ for (ch = 0; ch < 4; ch += 2) {
+ uint32_t nz_coeffs = 0;
+ tnz = mb->nz_ >> (4 + ch);
+ lnz = left_mb->nz_ >> (4 + ch);
+ for (y = 0; y < 2; ++y) {
+ int l = lnz & 1;
+ for (x = 0; x < 2; ++x) {
+ const int ctx = l + (tnz & 1);
+ const int nz = GetCoeffs(token_br, bands[2], ctx, q->uv_mat_, 0, dst);
+ l = (nz > 0);
+ tnz = (tnz >> 1) | (l << 3);
+ nz_coeffs = NzCodeBits(nz_coeffs, nz, dst[0] != 0);
+ dst += 16;
+ }
+ tnz >>= 2;
+ lnz = (lnz >> 1) | (l << 5);
+ }
+ // Note: we don't really need the per-4x4 details for U/V blocks.
+ non_zero_uv |= nz_coeffs << (4 * ch);
+ out_t_nz |= (tnz << 4) << ch;
+ out_l_nz |= (lnz & 0xf0) << ch;
+ }
+ mb->nz_ = out_t_nz;
+ left_mb->nz_ = out_l_nz;
+
+ block->non_zero_y_ = non_zero_y;
+ block->non_zero_uv_ = non_zero_uv;
+
+ // We look at the mode-code of each block and check if some blocks have less
+ // than three non-zero coeffs (code < 2). This is to avoid dithering flat and
+ // empty blocks.
+ block->dither_ = (non_zero_uv & 0xaaaa) ? 0 : q->dither_;
+
+ return !(non_zero_y | non_zero_uv); // will be used for further optimization
+}
+
+//------------------------------------------------------------------------------
+// Main loop
+
+int VP8DecodeMB(VP8Decoder* const dec, VP8BitReader* const token_br) {
+ VP8MB* const left = dec->mb_info_ - 1;
+ VP8MB* const mb = dec->mb_info_ + dec->mb_x_;
+ VP8MBData* const block = dec->mb_data_ + dec->mb_x_;
+ int skip = dec->use_skip_proba_ ? block->skip_ : 0;
+
+ if (!skip) {
+ skip = ParseResiduals(dec, mb, token_br);
+ } else {
+ left->nz_ = mb->nz_ = 0;
+ if (!block->is_i4x4_) {
+ left->nz_dc_ = mb->nz_dc_ = 0;
+ }
+ block->non_zero_y_ = 0;
+ block->non_zero_uv_ = 0;
+ block->dither_ = 0;
+ }
+
+ if (dec->filter_type_ > 0) { // store filter info
+ VP8FInfo* const finfo = dec->f_info_ + dec->mb_x_;
+ *finfo = dec->fstrengths_[block->segment_][block->is_i4x4_];
+ finfo->f_inner_ |= !skip;
+ }
+
+ return !token_br->eof_;
+}
+
+void VP8InitScanline(VP8Decoder* const dec) {
+ VP8MB* const left = dec->mb_info_ - 1;
+ left->nz_ = 0;
+ left->nz_dc_ = 0;
+ memset(dec->intra_l_, B_DC_PRED, sizeof(dec->intra_l_));
+ dec->mb_x_ = 0;
+}
+
+static int ParseFrame(VP8Decoder* const dec, VP8Io* io) {
+ for (dec->mb_y_ = 0; dec->mb_y_ < dec->br_mb_y_; ++dec->mb_y_) {
+ // Parse bitstream for this row.
+ VP8BitReader* const token_br =
+ &dec->parts_[dec->mb_y_ & dec->num_parts_minus_one_];
+ if (!VP8ParseIntraModeRow(&dec->br_, dec)) {
+ return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
+ "Premature end-of-partition0 encountered.");
+ }
+ for (; dec->mb_x_ < dec->mb_w_; ++dec->mb_x_) {
+ if (!VP8DecodeMB(dec, token_br)) {
+ return VP8SetError(dec, VP8_STATUS_NOT_ENOUGH_DATA,
+ "Premature end-of-file encountered.");
+ }
+ }
+ VP8InitScanline(dec); // Prepare for next scanline
+
+ // Reconstruct, filter and emit the row.
+ if (!VP8ProcessRow(dec, io)) {
+ return VP8SetError(dec, VP8_STATUS_USER_ABORT, "Output aborted.");
+ }
+ }
+ if (dec->mt_method_ > 0) {
+ if (!WebPGetWorkerInterface()->Sync(&dec->worker_)) return 0;
+ }
+
+ return 1;
+}
+
+// Main entry point
+int VP8Decode(VP8Decoder* const dec, VP8Io* const io) {
+ int ok = 0;
+ if (dec == NULL) {
+ return 0;
+ }
+ if (io == NULL) {
+ return VP8SetError(dec, VP8_STATUS_INVALID_PARAM,
+ "NULL VP8Io parameter in VP8Decode().");
+ }
+
+ if (!dec->ready_) {
+ if (!VP8GetHeaders(dec, io)) {
+ return 0;
+ }
+ }
+ assert(dec->ready_);
+
+ // Finish setting up the decoding parameter. Will call io->setup().
+ ok = (VP8EnterCritical(dec, io) == VP8_STATUS_OK);
+ if (ok) { // good to go.
+ // Will allocate memory and prepare everything.
+ if (ok) ok = VP8InitFrame(dec, io);
+
+ // Main decoding loop
+ if (ok) ok = ParseFrame(dec, io);
+
+ // Exit.
+ ok &= VP8ExitCritical(dec, io);
+ }
+
+ if (!ok) {
+ VP8Clear(dec);
+ return 0;
+ }
+
+ dec->ready_ = 0;
+ return ok;
+}
+
+void VP8Clear(VP8Decoder* const dec) {
+ if (dec == NULL) {
+ return;
+ }
+ WebPGetWorkerInterface()->End(&dec->worker_);
+ WebPDeallocateAlphaMemory(dec);
+ WebPSafeFree(dec->mem_);
+ dec->mem_ = NULL;
+ dec->mem_size_ = 0;
+ memset(&dec->br_, 0, sizeof(dec->br_));
+ dec->ready_ = 0;
+}
+
+//------------------------------------------------------------------------------