avcodec/pngdec: create a function to decode PLTE chunk.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/pngdec.c

@@ -671,6 +671,29 @@ static int decode_idat_chunk(AVCodecContext *avctx, PNGDecContext *s,
     return 0;
 }
 
+static int decode_plte_chunk(AVCodecContext *avctx, PNGDecContext *s,
+                             uint32_t length)
+{
+    int n, i, r, g, b;
+
+    if ((length % 3) != 0 || length > 256 * 3)
+        return AVERROR_INVALIDDATA;
+    /* read the palette */
+    n = length / 3;
+    for (i = 0; i < n; i++) {
+        r = bytestream2_get_byte(&s->gb);
+        g = bytestream2_get_byte(&s->gb);
+        b = bytestream2_get_byte(&s->gb);
+        s->palette[i] = (0xFFU << 24) | (r << 16) | (g << 8) | b;
+    }
+    for (; i < 256; i++)
+        s->palette[i] = (0xFFU << 24);
+    s->state |= PNG_PLTE;
+    bytestream2_skip(&s->gb, 4);     /* crc */
+
+    return 0;
+}
+
 static int decode_frame_png(AVCodecContext *avctx,
                         void *data, int *got_frame,
                         AVPacket *avpkt)
@@ -744,24 +767,8 @@ static int decode_frame_png(AVCodecContext *avctx,
                 goto fail;
             break;
         case MKTAG('P', 'L', 'T', 'E'):
-        {
-            int n, i, r, g, b;
-
-            if ((length % 3) != 0 || length > 256 * 3)
+            if (decode_plte_chunk(avctx, s, length) < 0)
                 goto skip_tag;
-            /* read the palette */
-            n = length / 3;
-            for (i = 0; i < n; i++) {
-                r = bytestream2_get_byte(&s->gb);
-                g = bytestream2_get_byte(&s->gb);
-                b = bytestream2_get_byte(&s->gb);
-                s->palette[i] = (0xFFU << 24) | (r << 16) | (g << 8) | b;
-            }
-            for (; i < 256; i++)
-                s->palette[i] = (0xFFU << 24);
-            s->state |= PNG_PLTE;
-            bytestream2_skip(&s->gb, 4);     /* crc */
-        }
         break;
         case MKTAG('t', 'R', 'N', 'S'):
         {