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Use new mbedtls_mpi_core_sub() instead of old static mpi_sub_hlp()

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Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
This commit is contained in:
Tom Cosgrove 2022-07-20 14:02:11 +01:00
parent 90c426b932
commit 7e655f7b4c
1 changed files with 2 additions and 36 deletions
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38
library/bignum.c
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@ -961,40 +961,6 @@ cleanup:
return( ret ); return( ret );
} }
/**
* Helper for mbedtls_mpi subtraction.
*
* Calculate l - r where l and r have the same size.
* This function operates modulo (2^ciL)^n and returns the carry
* (1 if there was a wraparound, i.e. if `l < r`, and 0 otherwise).
*
* d may be aliased to l or r.
*
* \param n Number of limbs of \p d, \p l and \p r.
* \param[out] d The result of the subtraction.
* \param[in] l The left operand.
* \param[in] r The right operand.
*
* \return 1 if `l < r`.
* 0 if `l >= r`.
*/
static mbedtls_mpi_uint mpi_sub_hlp( size_t n,
mbedtls_mpi_uint *d,
const mbedtls_mpi_uint *l,
const mbedtls_mpi_uint *r )
{
size_t i;
mbedtls_mpi_uint c = 0, t, z;
for( i = 0; i < n; i++ )
{
z = ( l[i] < c ); t = l[i] - c;
c = ( t < r[i] ) + z; d[i] = t - r[i];
}
return( c );
}
/* /*
* Unsigned subtraction: X = |A| - |B| (HAC 14.9, 14.10) * Unsigned subtraction: X = |A| - |B| (HAC 14.9, 14.10)
*/ */
@ -1027,7 +993,7 @@ int mbedtls_mpi_sub_abs( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
if( X->n > A->n ) if( X->n > A->n )
memset( X->p + A->n, 0, ( X->n - A->n ) * ciL ); memset( X->p + A->n, 0, ( X->n - A->n ) * ciL );
carry = mpi_sub_hlp( n, X->p, A->p, B->p ); carry = mbedtls_mpi_core_sub( X->p, A->p, B->p, n );
if( carry != 0 ) if( carry != 0 )
{ {
/* Propagate the carry to the first nonzero limb of X. */ /* Propagate the carry to the first nonzero limb of X. */
@ -1660,7 +1626,7 @@ static void mpi_montmul( mbedtls_mpi *A, const mbedtls_mpi *B, const mbedtls_mpi
* do the calculation without using conditional tests. */ * do the calculation without using conditional tests. */
/* Set d to d0 + (2^biL)^n - N where d0 is the current value of d. */ /* Set d to d0 + (2^biL)^n - N where d0 is the current value of d. */
d[n] += 1; d[n] += 1;
d[n] -= mpi_sub_hlp( n, d, d, N->p ); d[n] -= mbedtls_mpi_core_sub( d, d, N->p, n );
/* If d0 < N then d < (2^biL)^n /* If d0 < N then d < (2^biL)^n
* so d[n] == 0 and we want to keep A as it is. * so d[n] == 0 and we want to keep A as it is.
* If d0 >= N then d >= (2^biL)^n, and d <= (2^biL)^n + N < 2 * (2^biL)^n * If d0 >= N then d >= (2^biL)^n, and d <= (2^biL)^n + N < 2 * (2^biL)^n