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Bignum core: Break shift_r function out of the classic shift_r

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This commit contains the function prototype for mbedtls_mpi_core_shift_r,
and the implementation minimally modified from mbedtls_mpi_shift_r.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2022-09-21 15:36:16 +02:00
parent 2b751cfa46
commit 6641420951
2 changed files with 37 additions and 13 deletions
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35
library/bignum.c
View File

@ -770,27 +770,38 @@ cleanup:
* Right-shift: X >>= count
*/
int mbedtls_mpi_shift_r( mbedtls_mpi *X, size_t count )
{
MPI_VALIDATE_RET( X != NULL );
if( X->n != 0 )
mbedtls_mpi_core_shift_r( X->p, X->n, count );
return( 0 );
}
void mbedtls_mpi_core_shift_r( mbedtls_mpi_uint *X, size_t limbs,
size_t count )
{
size_t i, v0, v1;
mbedtls_mpi_uint r0 = 0, r1;
MPI_VALIDATE_RET( X != NULL );
v0 = count / biL;
v1 = count & (biL - 1);
if( v0 > X->n || ( v0 == X->n && v1 > 0 ) )
return mbedtls_mpi_lset( X, 0 );
if( v0 > limbs || ( v0 == limbs && v1 > 0 ) )
{
memset( X, 0, limbs * ciL );
return;
}
/*
* shift by count / limb_size
*/
if( v0 > 0 )
{
for( i = 0; i < X->n - v0; i++ )
X->p[i] = X->p[i + v0];
for( i = 0; i < limbs - v0; i++ )
X[i] = X[i + v0];
for( ; i < X->n; i++ )
X->p[i] = 0;
for( ; i < limbs; i++ )
X[i] = 0;
}
/*
@ -798,16 +809,14 @@ int mbedtls_mpi_shift_r( mbedtls_mpi *X, size_t count )
*/
if( v1 > 0 )
{
for( i = X->n; i > 0; i-- )
for( i = limbs; i > 0; i-- )
{
r1 = X->p[i - 1] << (biL - v1);
X->p[i - 1] >>= v1;
X->p[i - 1] |= r0;
r1 = X[i - 1] << (biL - v1);
X[i - 1] >>= v1;
X[i - 1] |= r0;
r0 = r1;
}
}
return( 0 );
}
/*

15
library/bignum_core.h
View File

@ -262,6 +262,21 @@ int mbedtls_mpi_core_write_be( const mbedtls_mpi_uint *A,
unsigned char *output,
size_t output_length );
/** \brief Shift a machine integer right by a number of bits.
*
* Shifting by more bits than there are bit positions
* in \p X is valid and results in setting \p X to 0.
*
* This function's execution time depends on the value
* of \p count (and of course \p limbs).
*
* \param[in,out] X The number to shift.
* \param limbs The number of limbs of \p X. This must be at least 1.
* \param count The number of bits to shift by.
*/
void mbedtls_mpi_core_shift_r( mbedtls_mpi_uint *X, size_t limbs,
size_t count );
/**
* \brief Conditional addition of two fixed-size large unsigned integers,
* returning the carry.