avformat/aviobuf: add ffio_read_leb() and ffio_write_leb()

Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/avio_internal.h

@@ -146,6 +146,16 @@ int ffio_rewind_with_probe_data(AVIOContext *s, unsigned char **buf, int buf_siz
 
 uint64_t ffio_read_varlen(AVIOContext *bc);
 
+/**
+ * Read a unsigned integer coded as a variable number of up to eight
+ * little-endian bytes, where the MSB in a byte signals another byte
+ * must be read.
+ * All coded bytes are read, but values > UINT_MAX are truncated.
+ */
+unsigned int ffio_read_leb(AVIOContext *s);
+
+void ffio_write_leb(AVIOContext *s, unsigned val);
+
 /**
  * Read size bytes from AVIOContext into buf.
  * Check that exactly size bytes have been read.

libavformat/aviobuf.c

@@ -971,6 +971,39 @@ uint64_t ffio_read_varlen(AVIOContext *bc){
     return val;
 }
 
+unsigned int ffio_read_leb(AVIOContext *s) {
+    int more, i = 0;
+    unsigned leb = 0;
+
+    do {
+        int byte = avio_r8(s);
+        unsigned bits = byte & 0x7f;
+        more = byte & 0x80;
+        if (i <= 4)
+            leb |= bits << (i * 7);
+        if (++i == 8)
+            break;
+    } while (more);
+
+    return leb;
+}
+
+void ffio_write_leb(AVIOContext *s, unsigned val)
+{
+    int len;
+    uint8_t byte;
+
+    len = (av_log2(val) + 7) / 7;
+
+    for (int i = 0; i < len; i++) {
+        byte = val >> (7 * i) & 0x7f;
+        if (i < len - 1)
+            byte |= 0x80;
+
+        avio_w8(s, byte);
+    }
+}
+
 int ffio_fdopen(AVIOContext **s, URLContext *h)
 {
     uint8_t *buffer = NULL;