bits: add fill_bits_buf() function

bits.c

@@ -60,6 +60,15 @@ void put_byte(struct bitreader *b, int v)
 	b->bitend += 8;
 }
 
+void fill_bits_buf(struct bitreader *b, int n)
+{
+	uint8_t *p = b->data;
+
+	while (b->bitend < b->bitpos + n)
+		put_byte(b, *p++);
+
+	b->data = p;
+}
 
 static void fill_bits(struct bitreader *b, int n)
 {

bits.h

@@ -37,6 +37,7 @@ struct bitreader {
 	void (*fill_bits)(struct bitreader *, int n);
 	void (*get_bits_cb)(uint64_t bits, int n);
 	void (*eof_cb)(void);
+	void *data;
 };
 
 void init_bits(struct bitreader *b);
@@ -46,6 +47,7 @@ int64_t get_sbits(struct bitreader *b, int n);
 uint32_t peek_bits(struct bitreader *b, unsigned n, unsigned offs);
 uint64_t peek_bits64(struct bitreader *b, unsigned n, unsigned offs);
 void put_byte(struct bitreader *b, int v);
+void fill_bits_buf(struct bitreader *b, int n);
 
 struct bitfield {
 	int size;