gst/matroska/: fix signed integer reading/writing.

Original commit message from CVS:
2004-01-02  Ronald Bultje  <rbultje@ronald.bitfreak.net>

* gst/matroska/ebml-read.c: (gst_ebml_read_sint):
* gst/matroska/ebml-write.c: (gst_ebml_write_sint):
fix signed integer reading/writing.

2 files changed, 17 insertions, 6 deletions

diff --git a/gst/matroska/ebml-read.c b/gst/matroska/ebml-read.c
index 67b9b5f3..c5b9c0da 100644
--- a/gst/matroska/ebml-read.c
+++ b/gst/matroska/ebml-read.c
@@ -464,7 +464,7 @@ gst_ebml_read_sint (GstEbmlRead *ebml,
 {
   GstBuffer *buf;
   guint8 *data;
-  guint size;
+  guint size, negative = 0, n = 0;
 
   if (!gst_ebml_read_buffer (ebml, id, &buf))
     return FALSE;
@@ -478,14 +478,19 @@ gst_ebml_read_sint (GstEbmlRead *ebml,
     gst_buffer_unref (buf);
     return FALSE;
   }
+  if (data[0] & 0x80) {
+    negative = 1;
+    data[0] &= ~0x80;
+  }
   *num = 0;
-  while (size > 0) {
-    *num = (*num << 8) | data[GST_BUFFER_SIZE (buf) - size];
-    size--;
+  while (n < size) {
+    *num = (*num << 8) | data[n++];
   }
 
   /* make signed */
-  *num -= (1LL << ((8 * GST_BUFFER_SIZE (buf)) - 1));
+  if (negative) {
+    *num = *num - (1LL << ((8 * size) - 1));
+  }
 
   gst_buffer_unref (buf);
 
diff --git a/gst/matroska/ebml-write.c b/gst/matroska/ebml-write.c
index 46cfd4a5..b6504867 100644
--- a/gst/matroska/ebml-write.c
+++ b/gst/matroska/ebml-write.c
@@ -391,7 +391,13 @@ gst_ebml_write_sint (GstEbmlWrite *ebml,
   guint size = gst_ebml_write_get_uint_size (unum);
 
   /* make unsigned */
-  unum = (num < 0 ? -num : num) + (1LLU << ((8 * size) - 1));
+  if (num >= 0) {
+    unum = num;
+  } else {
+    unum = 0x80 << (size - 1);
+    unum += num;
+    unum |= 0x80 << (size - 1);
+  }
 
   /* write */
   gst_ebml_write_element_id (buf, id);