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Merge pull request #6235 from tom-cosgrove-arm/issue-6231-core-sub-int

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Bignum: extract core_sub_int from the prototype
This commit is contained in:
Janos Follath
2022-11-23 13:32:02 +00:00
committed by GitHub
parent ef25a99f20 d66d5b2fef
commit 531a871b88
5 changed files with 115 additions and 7 deletions
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12
library/bignum.c
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@ -968,17 +968,15 @@ int mbedtls_mpi_sub_abs( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
carry = mbedtls_mpi_core_sub( X->p, A->p, B->p, n );
if( carry != 0 )
{
/* Propagate the carry to the first nonzero limb of X. */
for( ; n < X->n && X->p[n] == 0; n++ )
--X->p[n];
/* If we ran out of space for the carry, it means that the result
* is negative. */
if( n == X->n )
/* Propagate the carry through the rest of X. */
carry = mbedtls_mpi_core_sub_int( X->p + n, X->p + n, carry, X->n - n );
/* If we have further carry/borrow, the result is negative. */
if( carry != 0 )
{
ret = MBEDTLS_ERR_MPI_NEGATIVE_VALUE;
goto cleanup;
}
--X->p[n];
}
/* X should always be positive as a result of unsigned subtractions. */

16
library/bignum_core.c
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@ -590,6 +590,22 @@ cleanup:
/* BEGIN MERGE SLOT 3 */
mbedtls_mpi_uint mbedtls_mpi_core_sub_int( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
mbedtls_mpi_uint c, /* doubles as carry */
size_t limbs )
{
for( size_t i = 0; i < limbs; i++ )
{
mbedtls_mpi_uint s = A[i];
mbedtls_mpi_uint t = s - c;
c = ( t > s );
X[i] = t;
}
return( c );
}
/* END MERGE SLOT 3 */
/* BEGIN MERGE SLOT 4 */

17
library/bignum_core.h
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@ -504,6 +504,23 @@ int mbedtls_mpi_core_fill_random( mbedtls_mpi_uint *X, size_t X_limbs,
/* BEGIN MERGE SLOT 3 */
/**
* \brief Subtract unsigned integer from known-size large unsigned integers.
* Return the borrow.
*
* \param[out] X The result of the subtraction.
* \param[in] A The left operand.
* \param b The unsigned scalar to subtract.
* \param limbs Number of limbs of \p X and \p A.
*
* \return 1 if `A < b`.
* 0 if `A >= b`.
*/
mbedtls_mpi_uint mbedtls_mpi_core_sub_int( mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
mbedtls_mpi_uint b,
size_t limbs );
/* END MERGE SLOT 3 */
/* BEGIN MERGE SLOT 4 */