1 files changed, 53 insertions, 0 deletions
diff --git a/Src/nsavi/read.cpp b/Src/nsavi/read.cpp
new file mode 100644
index 00000000..8790d5e0
--- /dev/null
+++ b/Src/nsavi/read.cpp
@@ -0,0 +1,53 @@
+#include "read.h"
+
+
+/* helper macro to do a read, check error code and number of bytes read, and return from the function if necessary 
+  has to be a macro because of the return */
+
+#define NSAVI_READ(reader, buffer, size, bytes_read) { int ret = reader->Read(buffer, size, &bytes_read); if (ret) return ret; if (bytes_read != size) return READ_EOF; }
+
+int nsavi::read_riff_chunk(nsavi::avi_reader *reader, nsavi::riff_chunk *chunk, uint32_t *out_bytes_read)
+{
+	uint32_t total_bytes_read=0;
+	uint32_t bytes_read;
+	NSAVI_READ(reader, chunk, 8, bytes_read); // read id and size
+	total_bytes_read += bytes_read;
+
+	if (chunk->id == 'FFIR' || chunk->id == 'TSIL')
+	{
+		if (chunk->size < 4)
+			return READ_INVALID_DATA;
+		NSAVI_READ(reader, &chunk->type, 4, bytes_read);
+		total_bytes_read += bytes_read;
+		chunk->size -= 4;
+	}
+	else
+		chunk->type = 0;
+
+	if (out_bytes_read)
+		*out_bytes_read = total_bytes_read;
+	return READ_OK;
+}
+
+// we pass riff_chunk instead of size
+// to avoid any confusion about who is responsible for adding the padding byte
+// (this function is responsible)
+int nsavi::skip_chunk(nsavi::avi_reader *reader, const nsavi::riff_chunk *chunk, uint32_t *out_bytes_read)
+{
+	uint32_t chunk_size = chunk->size;
+	if (chunk_size & 1)
+	{
+		chunk_size ++;  // odd chunk sizes must be padded by one
+		if (chunk_size == 0) // check for overflow
+			return READ_INVALID_DATA;
+	}
+
+	int ret = reader->Skip(chunk_size);
+	if (ret)
+		return ret;
+
+	if (out_bytes_read)
+		*out_bytes_read = chunk_size;
+	return READ_OK;
+}
+