extern struct sha1file *sha1fd_check(const char *name);
extern struct sha1file *sha1fd_throughput(int fd, const char *name, struct progress *tp);
extern int sha1close(struct sha1file *, unsigned char *, unsigned int);
-extern void sha1write(struct sha1file *, void *, unsigned int);
+extern void sha1write(struct sha1file *, const void *, unsigned int);
extern void sha1flush(struct sha1file *f);
extern void crc32_begin(struct sha1file *);
extern uint32_t crc32_end(struct sha1file *);