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mpi_exp_mod: remove the 'one' variable

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Signed-off-by: Janos Follath <janos.follath@arm.com>
This commit is contained in:
Janos Follath 2022-11-21 15:54:20 +00:00
parent b2c2fca974
commit 74601209fa
1 changed files with 10 additions and 5 deletions
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15
library/bignum.c
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@ -1970,7 +1970,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
mbedtls_mpi *prec_RR ) mbedtls_mpi *prec_RR )
{ {
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
size_t window_bitsize, one = 1; size_t window_bitsize;
size_t i, j, nblimbs; size_t i, j, nblimbs;
size_t bufsize, nbits; size_t bufsize, nbits;
mbedtls_mpi_uint ei, mm, state; mbedtls_mpi_uint ei, mm, state;
@ -2091,9 +2091,12 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
if( window_bitsize > 1 ) if( window_bitsize > 1 )
{ {
/* /*
* W[1 << (window_bitsize - 1)] = W[1] ^ (window_bitsize - 1) * W[i] = W[1] ^ i
*
* The first bit of the sliding window is always 1 and therefore we
* only need to store the second half of the table.
*/ */
j = one << ( window_bitsize - 1 ); j = w_table_used_size / 2;
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[j], N->n + 1 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[j], N->n + 1 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[j], &W[1] ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[j], &W[1] ) );
@ -2103,8 +2106,10 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
/* /*
* W[i] = W[i - 1] * W[1] * W[i] = W[i - 1] * W[1]
* (The last element in the table is for the result X, so we don't need
* to calculate that.)
*/ */
for( i = j + 1; i < ( one << window_bitsize ); i++ ) for( i = j + 1; i < w_table_used_size - 1; i++ )
{ {
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[i], N->n + 1 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[i], N->n + 1 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[i], &W[i - 1] ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[i], &W[i - 1] ) );
@ -2194,7 +2199,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
exponent_bits_in_window <<= 1; exponent_bits_in_window <<= 1;
if( ( exponent_bits_in_window & ( one << window_bitsize ) ) != 0 ) if( ( exponent_bits_in_window & ( (size_t) 1 << window_bitsize ) ) != 0 )
{ {
MBEDTLS_MPI_CHK( mpi_select( &WW, W, w_table_used_size, 1 ) ); MBEDTLS_MPI_CHK( mpi_select( &WW, W, w_table_used_size, 1 ) );
mpi_montmul( &W[x_index], &WW, N, mm, &T ); mpi_montmul( &W[x_index], &WW, N, mm, &T );