Uses k_size as an signed integer buf_incrwritepos() and mp_to_unsigned_bin() functions use k_size as signed integer argument. k_size is also used in an assertion that compared it to curve_size which is a signed long. Only buf_getwriteptr() is using k_size as unsigned. So it safe to use it as signed.

480        87
960       111
1440       135
1920       159
2400       200
2880       224
3360       248
3840       272
4320       296
4800       320
5280       344
5760       368
6240       392
6720       416
7200       440
7680       464