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Use less memory in fix_negative()

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Manuel Pégourié-Gonnard 2013-10-23 20:45:04 +02:00
parent cae6f3ed45
commit b21c81fb41
1 changed files with 16 additions and 12 deletions
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28
library/ecp.c
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@ -1736,12 +1736,20 @@ static inline void sub32( uint32_t *dst, uint32_t src, signed char *carry )
/*
* Helpers for the main 'loop'
* (see fix_negative for the motivation of C)
*/
#define INIT( b ) \
int ret; \
signed char c = 0, cc; \
uint32_t cur; \
size_t i = 0, bits = b; \
mpi C; \
t_uint Cp[ b / 8 / sizeof( t_uint) + 1 ]; \
\
C.s = 1; \
C.n = b / 8 / sizeof( t_uint) + 1; \
C.p = Cp; \
memset( Cp, 0, C.n * sizeof( t_uint ) ); \
\
MPI_CHK( mpi_grow( N, b * 2 / 8 / sizeof( t_uint ) ) ); \
LOAD32;
@ -1758,32 +1766,28 @@ static inline void sub32( uint32_t *dst, uint32_t src, signed char *carry )
STORE32; i++; \
cur = c > 0 ? c : 0; STORE32; \
cur = 0; while( ++i < MAX32 ) { STORE32; } \
if( c < 0 ) fix_negative( N, c, bits );
if( c < 0 ) fix_negative( N, c, &C, bits );
/*
* If the result is negative, we get it in the form
* c * 2^(bits + 32) + N, with c negative and N positive shorter than 'bits'
*/
static inline int fix_negative( mpi *N, signed char c, size_t bits )
static inline int fix_negative( mpi *N, signed char c, mpi *C, size_t bits )
{
int ret;
mpi C;
t_uint Cp[ 384 / 8 / sizeof( t_uint) + 1 ];
/* C = - c * 2^(bits + 32) */
C.s = 1;
C.n = bits / 8 / sizeof( t_uint ) + 1;
C.p = Cp;
memset( Cp, 0, C.n * sizeof( t_uint ) );
#if defined(POLARSSL_HAVE_INT64)
#if !defined(POLARSSL_HAVE_INT64)
((void) bits);
#else
if( bits == 224 )
Cp[ C.n - 1 ] = ((t_uint) -c) << 32;
C->p[ C->n - 1 ] = ((t_uint) -c) << 32;
else
#endif
Cp[ C.n - 1 ] = (t_uint) -c;
C->p[ C->n - 1 ] = (t_uint) -c;
/* N = - ( C - N ) */
MPI_CHK( mpi_sub_abs( N, &C, N ) );
MPI_CHK( mpi_sub_abs( N, C, N ) );
N->s = -1;
cleanup: