Distinguish between non-coded blocks and decode errors in rtjpeg's get_block

Originally committed as revision 18926 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/rtjpeg.c

@@ -38,6 +38,7 @@
  * \param block where data is written to
  * \param scan array containing the mapping stream address -> block position
  * \param quant quantization factors
+ * \return 0 means the block is not coded, < 0 means an error occurred.
  *
  * Note: GetBitContext is used to make the code simpler, since all data is
  * aligned this could be done faster in a different way, e.g. as it is done
@@ -56,7 +57,7 @@ static inline int get_block(GetBitContext *gb, DCTELEM *block, const uint8_t *sc
     // number of non-zero coefficients
     coeff = get_bits(gb, 6);
     if (get_bits_count(gb) + (coeff << 1) >= gb->size_in_bits)
-        return 0;
+        return -1;
 
     // normally we would only need to clear the (63 - coeff) last values,
     // but since we do not know where they are we just clear the whole block
@@ -73,7 +74,7 @@ static inline int get_block(GetBitContext *gb, DCTELEM *block, const uint8_t *sc
     // 4 bits per coefficient
     ALIGN(4);
     if (get_bits_count(gb) + (coeff << 2) >= gb->size_in_bits)
-        return 0;
+        return -1;
     while (coeff) {
         ac = get_sbits(gb, 4);
         if (ac == -8)
@@ -84,7 +85,7 @@ static inline int get_block(GetBitContext *gb, DCTELEM *block, const uint8_t *sc
     // 8 bits per coefficient
     ALIGN(8);
     if (get_bits_count(gb) + (coeff << 3) >= gb->size_in_bits)
-        return 0;
+        return -1;
     while (coeff) {
         ac = get_sbits(gb, 8);
         PUT_COEFF(ac);
@@ -114,22 +115,22 @@ int rtjpeg_decode_frame_yuv420(RTJpegContext *c, AVFrame *f,
     for (y = 0; y < h; y++) {
         for (x = 0; x < w; x++) {
             DCTELEM *block = c->block;
-            if (get_block(&gb, block, c->scan, c->lquant))
+            if (get_block(&gb, block, c->scan, c->lquant) > 0)
                 c->dsp->idct_put(y1, f->linesize[0], block);
             y1 += 8;
-            if (get_block(&gb, block, c->scan, c->lquant))
+            if (get_block(&gb, block, c->scan, c->lquant) > 0)
                 c->dsp->idct_put(y1, f->linesize[0], block);
             y1 += 8;
-            if (get_block(&gb, block, c->scan, c->lquant))
+            if (get_block(&gb, block, c->scan, c->lquant) > 0)
                 c->dsp->idct_put(y2, f->linesize[0], block);
             y2 += 8;
-            if (get_block(&gb, block, c->scan, c->lquant))
+            if (get_block(&gb, block, c->scan, c->lquant) > 0)
                 c->dsp->idct_put(y2, f->linesize[0], block);
             y2 += 8;
-            if (get_block(&gb, block, c->scan, c->cquant))
+            if (get_block(&gb, block, c->scan, c->cquant) > 0)
                 c->dsp->idct_put(u, f->linesize[1], block);
             u += 8;
-            if (get_block(&gb, block, c->scan, c->cquant))
+            if (get_block(&gb, block, c->scan, c->cquant) > 0)
                 c->dsp->idct_put(v, f->linesize[2], block);
             v += 8;
         }