lib/mpi: mpi_read_raw_data(): fix nbits calculation
authorNicolai Stange <nicstange@gmail.com>
Thu, 26 May 2016 11:05:32 +0000 (13:05 +0200)
committerHerbert Xu <herbert@gondor.apana.org.au>
Tue, 31 May 2016 08:41:59 +0000 (16:41 +0800)
commiteef0df6a59537032ab6b708f30b28d9530f8760e
tree3028a30022c96d7443a389dc7eff94cef65f2bd0
parentdfd90510672f69206942546e8df4f63cfa91eae6
lib/mpi: mpi_read_raw_data(): fix nbits calculation

The number of bits, nbits, is calculated in mpi_read_raw_data() as follows:

  nbits = nbytes * 8;

Afterwards, the number of leading zero bits of the first byte get
subtracted:

  nbits -= count_leading_zeros(buffer[0]);

However, count_leading_zeros() takes an unsigned long and thus,
the u8 gets promoted to an unsigned long.

Thus, the above doesn't subtract the number of leading zeros in the most
significant nonzero input byte from nbits, but the number of leading
zeros of the most significant nonzero input byte promoted to unsigned long,
i.e. BITS_PER_LONG - 8 too many.

Fix this by subtracting

  count_leading_zeros(...) - (BITS_PER_LONG - 8)

from nbits only.

Fixes: e1045992949 ("MPILIB: Provide a function to read raw data into an
                     MPI")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
lib/mpi/mpicoder.c