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mbedtls_mpi_mul_hlp: no microoptimization

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Note a possible microoptimization in mbedtls_mpi_mul_hlp that I tried
in the hope of reducing the number of allocations, but turned out to
be counterproductive.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2020-07-24 00:09:04 +02:00
parent 8e464c407a
commit cd0dbf36b6
1 changed files with 8 additions and 0 deletions
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8
library/bignum.c
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@ -1676,6 +1676,14 @@ int mbedtls_mpi_mul_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_uint
/* Calculate X*b as A + A*(b-1) to take advantage of mpi_mul_hlp */ /* Calculate X*b as A + A*(b-1) to take advantage of mpi_mul_hlp */
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
/* In general, A * b requires 1 limb more than b. If
* A->p[n - 1] * b / b == A->p[n - 1], then A * b fits in the same
* number of limbs as A and the call to grow() is not required since
* copy() will take care of the growth. However, experimentally,
* making the call to grow() conditional causes slightly fewer
* calls to calloc() in ECP code, presumably because it reuses the
* same mpi for a while and this way the mpi is more likely to directly
* grow to its final size. */
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, n + 1 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, n + 1 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( X, A ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( X, A ) );
mpi_mul_hlp( n, A->p, X->p, b - 1 ); mpi_mul_hlp( n, A->p, X->p, b - 1 );