wtv: Seek by sector properly

Use an helper function to seek by sector to avoid possible mistakes
due shifting by WTV_SECTOR_BITS a 32bit integer.

Contrary to common intuition, a 32 bit integer left shifted
by a 64 bit integer does not promote the 32 bit integer to
64 bit before shifting.

libavformat/wtv.c

@@ -48,10 +48,12 @@
  *
  */
 
-#define WTV_SECTOR_BITS    INT64_C(12)
+#define WTV_SECTOR_BITS    12
 #define WTV_SECTOR_SIZE    (1 << WTV_SECTOR_BITS)
 #define WTV_BIGSECTOR_BITS 18
 
+#define SHIFT_SECTOR_BITS(a) ((int64_t)(a) << WTV_SECTOR_BITS)
+
 typedef struct {
     AVIOContext *pb_filesystem;  /** file system (AVFormatContext->pb) */
 
@@ -64,6 +66,11 @@ typedef struct {
     int64_t length;
 } WtvFile;
 
+static int64_t seek_by_sector(AVIOContext *pb, int64_t sector, int64_t offset)
+{
+    return avio_seek(pb, SHIFT_SECTOR_BITS(sector) + offset, SEEK_SET);
+}
+
 /**
  * @return bytes read, 0 on end of file, or <0 on error
  */
@@ -94,7 +101,7 @@ static int wtvfile_read_packet(void *opaque, uint8_t *buf, int buf_size)
             int i = wf->position >> wf->sector_bits;
             if (i >= wf->nb_sectors ||
                 (wf->sectors[i] != wf->sectors[i - 1] + (1 << (wf->sector_bits - WTV_SECTOR_BITS)) &&
-                avio_seek(pb, wf->sectors[i] << WTV_SECTOR_BITS, SEEK_SET) < 0)) {
+                seek_by_sector(pb, wf->sectors[i], 0) < 0)) {
                 wf->error = 1;
                 break;
             }
@@ -119,8 +126,8 @@ static int64_t wtvfile_seek(void *opaque, int64_t offset, int whence)
         offset = wf->length;
 
     wf->error = offset < 0 || offset >= wf->length ||
-                avio_seek(pb, (wf->sectors[offset >> wf->sector_bits] << WTV_SECTOR_BITS)
-                              + (offset & ((1 << wf->sector_bits) - 1)), SEEK_SET) < 0;
+                seek_by_sector(pb, wf->sectors[offset >> wf->sector_bits],
+                               offset & ((1 << wf->sector_bits) - 1)) < 0;
     wf->position = offset;
     return offset;
 }
@@ -155,7 +162,7 @@ static AVIOContext * wtvfile_open_sector(int first_sector, uint64_t length, int
     WtvFile *wf;
     uint8_t *buffer;
 
-    if (avio_seek(s->pb, first_sector << WTV_SECTOR_BITS, SEEK_SET) < 0)
+    if (seek_by_sector(s->pb, first_sector, 0) < 0)
         return NULL;
 
     wf = av_mallocz(sizeof(WtvFile));
@@ -184,14 +191,14 @@ static AVIOContext * wtvfile_open_sector(int first_sector, uint64_t length, int
         int nb_sectors1 = read_ints(s->pb, sectors1, WTV_SECTOR_SIZE / 4);
         int i;
 
-        wf->sectors = av_malloc(nb_sectors1 << WTV_SECTOR_BITS);
+        wf->sectors = av_malloc(SHIFT_SECTOR_BITS(nb_sectors1));
         if (!wf->sectors) {
             av_free(wf);
             return NULL;
         }
         wf->nb_sectors = 0;
         for (i = 0; i < nb_sectors1; i++) {
-            if (avio_seek(s->pb, sectors1[i] << WTV_SECTOR_BITS, SEEK_SET) < 0)
+            if (seek_by_sector(s->pb, sectors1[i], 0) < 0)
                 break;
             wf->nb_sectors += read_ints(s->pb, wf->sectors + i * WTV_SECTOR_SIZE / 4, WTV_SECTOR_SIZE / 4);
         }
@@ -218,7 +225,7 @@ static AVIOContext * wtvfile_open_sector(int first_sector, uint64_t length, int
 
     /* seek to initial sector */
     wf->position = 0;
-    if (avio_seek(s->pb, wf->sectors[0] << WTV_SECTOR_BITS, SEEK_SET) < 0) {
+    if (seek_by_sector(s->pb, wf->sectors[0], 0) < 0) {
         av_free(wf->sectors);
         av_free(wf);
         return NULL;
@@ -963,7 +970,7 @@ static int read_header(AVFormatContext *s)
     avio_skip(s->pb, 4);
     root_sector = avio_rl32(s->pb);
 
-    avio_seek(s->pb, root_sector << WTV_SECTOR_BITS, SEEK_SET);
+    seek_by_sector(s->pb, root_sector, 0);
     root_size = avio_read(s->pb, root, root_size);
     if (root_size < 0)
         return AVERROR_INVALIDDATA;