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Rework ecp_mod_p192()

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On x86_64, this makes it 5x faster, and ecp_mul() 17% faster for this curve.
The code is shorter too.
This commit is contained in:
Manuel Pégourié-Gonnard
2013-10-22 21:03:16 +02:00
parent 6888167e73
commit d1e7a45fdd
2 changed files with 56 additions and 59 deletions
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101
library/ecp.c
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@ -475,25 +475,36 @@ cleanup:
}
#if defined(POLARSSL_ECP_DP_SECP192R1_ENABLED)
/*
* 192 bits in terms of t_uint
*/
#define P192_SIZE_INT ( 192 / CHAR_BIT / sizeof( t_uint ) )
/*
* Table to get S1, S2, S3 of FIPS 186-3 D.2.1:
* -1 means let this chunk be 0
* a positive value i means A_i.
*/
#define P192_CHUNKS 3
#define P192_CHUNK_CHAR ( 64 / CHAR_BIT )
#define P192_CHUNK_INT ( P192_CHUNK_CHAR / sizeof( t_uint ) )
/* Add 64-bit chunks (dst += src) and update carry */
static inline void add_64( t_uint *dst, t_uint *src, t_uint *carry )
{
unsigned char i;
t_uint c = 0;
for( i = 0; i < 8 / sizeof( t_uint ); i++, dst++, src++ )
{
*dst += c; c = ( *dst < c );
*dst += *src; c += ( *dst < *src );
}
*carry += c;
}
const signed char p192_tbl[][P192_CHUNKS] = {
{ -1, 3, 3 }, /* S1 */
{ 4, 4, -1 }, /* S2 */
{ 5, 5, 5 }, /* S3 */
};
/* Add carry to a 64-bit chunk and update carry */
static inline void carry64( t_uint *dst, t_uint *carry )
{
unsigned char i;
for( i = 0; i < 8 / sizeof( t_uint ); i++, dst++ )
{
*dst += *carry;
*carry = ( *dst < *carry );
}
}
#define OFFSET ( 8 / sizeof( t_uint ) )
#define A( i ) ( N->p + ( i ) * OFFSET )
#define ADD( i ) add_64( p, A( i ), &c )
#define NEXT p += OFFSET; carry64( p, &c )
#define LAST p += OFFSET; *p = c; while( ++p < end ) *p = 0
/*
* Fast quasi-reduction modulo p192 (FIPS 186-3 D.2.1)
@ -501,53 +512,27 @@ const signed char p192_tbl[][P192_CHUNKS] = {
static int ecp_mod_p192( mpi *N )
{
int ret;
unsigned char i, j, offset;
signed char chunk;
mpi tmp, acc;
t_uint tmp_p[P192_SIZE_INT], acc_p[P192_SIZE_INT + 1];
t_uint c = 0;
t_uint *p, *end;
tmp.s = 1;
tmp.n = sizeof( tmp_p ) / sizeof( tmp_p[0] );
tmp.p = tmp_p;
/* Make sure we have the correct number of blocks */
MPI_CHK( mpi_grow( N, 6 * OFFSET ) );
p = N->p;
end = p + N->n;
acc.s = 1;
acc.n = sizeof( acc_p ) / sizeof( acc_p[0] );
acc.p = acc_p;
MPI_CHK( mpi_grow( N, P192_SIZE_INT * 2 ) );
/*
* acc = T
*/
memset( acc_p, 0, sizeof( acc_p ) );
memcpy( acc_p, N->p, P192_CHUNK_CHAR * P192_CHUNKS );
for( i = 0; i < sizeof( p192_tbl ) / sizeof( p192_tbl[0] ); i++)
{
/*
* tmp = S_i
*/
memset( tmp_p, 0, sizeof( tmp_p ) );
for( j = 0, offset = P192_CHUNKS - 1; j < P192_CHUNKS; j++, offset-- )
{
chunk = p192_tbl[i][j];
if( chunk >= 0 )
memcpy( tmp_p + offset * P192_CHUNK_INT,
N->p + chunk * P192_CHUNK_INT,
P192_CHUNK_CHAR );
}
/*
* acc += tmp
*/
MPI_CHK( mpi_add_abs( &acc, &acc, &tmp ) );
}
MPI_CHK( mpi_copy( N, &acc ) );
ADD( 3 ); ADD( 5 ); NEXT; // A0 += A3 + A5
ADD( 3 ); ADD( 4 ); ADD( 5 ); NEXT; // A1 += A3 + A4 + A5
ADD( 4 ); ADD( 5 ); LAST; // A2 += A4 + A5
cleanup:
return( ret );
}
#undef OFFSET
#undef A
#undef ADD
#undef NEXT
#undef LAST
#endif /* POLARSSL_ECP_DP_SECP192R1_ENABLED */
#if defined(POLARSSL_ECP_DP_SECP521R1_ENABLED)