Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1407520 > unrolled thread

[PATCH 1/2] lib/mpi: mpi_read_raw_data(): purge redundant clearing of nbits

Back to article view | Back to linux.kernel

Contents

  [PATCH 1/2] lib/mpi: mpi_read_raw_data(): purge redundant clearing of nbits Nicolai Stange <nicstange@gmail.com> - 2016-05-26 13:10 +0200
    [PATCH 2/2] lib/mpi: mpi_read_raw_data(): fix nbits calculation Nicolai Stange <nicstange@gmail.com> - 2016-05-26 13:10 +0200

#1407520 — [PATCH 1/2] lib/mpi: mpi_read_raw_data(): purge redundant clearing of nbits

In mpi_read_raw_data(), unsigned nbits is calculated as follows:

 nbits = nbytes * 8;

and redundantly cleared later on if nbytes == 0:

  if (nbytes > 0)
    ...
  else
    nbits = 0;

Purge this redundant clearing for the sake of clarity.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
---
 Applicable to linux-next-20160525.

 lib/mpi/mpicoder.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index 747606f..c160393 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -51,8 +51,6 @@ MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
 	}
 	if (nbytes > 0)
 		nbits -= count_leading_zeros(buffer[0]);
-	else
-		nbits = 0;
 
 	nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 	val = mpi_alloc(nlimbs);
-- 
2.8.2

[toc] | [next] | [standalone]

#1407522 — [PATCH 2/2] 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>
---
 Applicable to linux-next-20150525.

 lib/mpi/mpicoder.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index c160393..d197210 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -50,7 +50,7 @@ MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
 		return NULL;
 	}
 	if (nbytes > 0)
-		nbits -= count_leading_zeros(buffer[0]);
+		nbits -= count_leading_zeros(buffer[0]) - (BITS_PER_LONG - 8);
 
 	nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 	val = mpi_alloc(nlimbs);
-- 
2.8.2

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web