lzw: switch to bytestream2

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org

libavcodec/lzw.c

@@ -28,6 +28,7 @@
  */
 
 #include "avcodec.h"
+#include "bytestream.h"
 #include "lzw.h"
 #include "libavutil/mem.h"
 
@@ -43,7 +44,7 @@ static const uint16_t mask[17] =
 };
 
 struct LZWState {
-    const uint8_t *buf_start, *pbuf, *ebuf;
+    GetByteContext gb;
     int bbits;
     unsigned int bbuf;
 
@@ -73,9 +74,9 @@ static int lzw_get_code(struct LZWState * s)
     if(s->mode == FF_LZW_GIF) {
         while (s->bbits < s->cursize) {
             if (!s->bs) {
-                s->bs = *s->pbuf++;
+                s->bs = bytestream2_get_byte(&s->gb);
             }
-            s->bbuf |= (*s->pbuf++) << s->bbits;
+            s->bbuf |= bytestream2_get_byte(&s->gb) << s->bbits;
             s->bbits += 8;
             s->bs--;
         }
@@ -83,7 +84,7 @@ static int lzw_get_code(struct LZWState * s)
         s->bbuf >>= s->cursize;
     } else { // TIFF
         while (s->bbits < s->cursize) {
-            s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
+            s->bbuf = (s->bbuf << 8) | bytestream2_get_byte(&s->gb);
             s->bbits += 8;
         }
         c = s->bbuf >> (s->bbits - s->cursize);
@@ -95,7 +96,7 @@ static int lzw_get_code(struct LZWState * s)
 int ff_lzw_size_read(LZWState *p)
 {
     struct LZWState *s = p;
-    return s->pbuf - s->buf_start;
+    return bytestream2_tell(&s->gb);
 }
 
 void ff_lzw_decode_tail(LZWState *p)
@@ -103,17 +104,12 @@ void ff_lzw_decode_tail(LZWState *p)
     struct LZWState *s = (struct LZWState *)p;
 
     if(s->mode == FF_LZW_GIF) {
-        while (s->bs > 0) {
-            if (s->bs >= s->ebuf - s->pbuf) {
-                s->pbuf = s->ebuf;
-                break;
-            } else {
-                s->pbuf += s->bs;
-                s->bs = *s->pbuf++;
-            }
+        while (s->bs > 0 && bytestream2_get_bytes_left(&s->gb)) {
+            bytestream2_skip(&s->gb, s->bs);
+            s->bs = bytestream2_get_byte(&s->gb);
         }
     }else
-        s->pbuf= s->ebuf;
+        bytestream2_skip(&s->gb, bytestream2_get_bytes_left(&s->gb));
 }
 
 av_cold void ff_lzw_decode_open(LZWState **p)
@@ -141,8 +137,7 @@ int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size,
     if(csize < 1 || csize >= LZW_MAXBITS)
         return -1;
     /* read buffer */
-    s->pbuf = buf;
-    s->ebuf = s->pbuf + buf_size;
+    bytestream2_init(&s->gb, buf, buf_size);
     s->bbuf = 0;
     s->bbits = 0;
     s->bs = 0;