From eef0df6a59537032ab6b708f30b28d9530f8760e Mon Sep 17 00:00:00 2001
From: Nicolai Stange <nicstange@gmail.com>
Date: Thu, 26 May 2016 13:05:32 +0200
Subject: 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 | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
(limited to 'lib/mpi/mpicoder.c')
diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index 37d6a4edb33c..eda34aba017e 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);
--
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