diff options
Diffstat (limited to 'mpi/mpi-mpow.c')
| -rw-r--r-- | mpi/mpi-mpow.c | 129 |
1 files changed, 4 insertions, 125 deletions
diff --git a/mpi/mpi-mpow.c b/mpi/mpi-mpow.c index a8c561dd1..001802191 100644 --- a/mpi/mpi-mpow.c +++ b/mpi/mpi-mpow.c @@ -1,5 +1,5 @@ /* mpi-mpow.c - MPI functions - * Copyright (C) 1998, 1999 Free Software Foundation, Inc. + * Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc. * * This file is part of GnuPG. * @@ -25,22 +25,6 @@ #include "longlong.h" #include <assert.h> -/* Barrett is slower than the classical way. It can be tweaked by - * using partial multiplications - */ -/*#define USE_BARRETT*/ - - - -#ifdef USE_BARRETT -static void barrett_mulm( MPI w, MPI u, MPI v, MPI m, MPI y, int k, MPI r1, MPI r2 ); -static MPI init_barrett( MPI m, int *k, MPI *r1, MPI *r2 ); -static int calc_barrett( MPI r, MPI x, MPI m, MPI y, int k, MPI r1, MPI r2 ); -#else -#define barrett_mulm( w, u, v, m, y, k, r1, r2 ) mpi_mulm( (w), (u), (v), (m) ) -#endif - - static int build_index( MPI *exparray, int k, int i, int t ) { @@ -53,7 +37,6 @@ build_index( MPI *exparray, int k, int i, int t ) if( mpi_test_bit( exparray[j], bitno ) ) index |= 1; } - /*log_debug("t=%d i=%d index=%d\n", t, i, index );*/ return index; } @@ -68,35 +51,25 @@ mpi_mulpowm( MPI res, MPI *basearray, MPI *exparray, MPI m) int i, j, idx; MPI *G; /* table with precomputed values of size 2^k */ MPI tmp; - #ifdef USE_BARRETT - MPI barrett_y, barrett_r1, barrett_r2; - int barrett_k; - #endif for(k=0; basearray[k]; k++ ) ; assert(k); for(t=0, i=0; (tmp=exparray[i]); i++ ) { - /*log_mpidump("exp: ", tmp );*/ j = mpi_get_nbits(tmp); if( j > t ) t = j; } - /*log_mpidump("mod: ", m );*/ assert(i==k); assert(t); assert( k < 10 ); G = m_alloc_clear( (1<<k) * sizeof *G ); - #ifdef USE_BARRETT - barrett_y = init_barrett( m, &barrett_k, &barrett_r1, &barrett_r2 ); - #endif /* and calculate */ tmp = mpi_alloc( mpi_get_nlimbs(m)+1 ); mpi_set_ui( res, 1 ); for(i = 1; i <= t; i++ ) { - barrett_mulm(tmp, res, res, m, barrett_y, barrett_k, - barrett_r1, barrett_r2 ); + mpi_mulm(tmp, res, res, m ); idx = build_index( exparray, k, i, t ); assert( idx >= 0 && idx < (1<<k) ); if( !G[idx] ) { @@ -108,115 +81,21 @@ mpi_mulpowm( MPI res, MPI *basearray, MPI *exparray, MPI m) if( !G[idx] ) G[idx] = mpi_copy( basearray[j] ); else - barrett_mulm( G[idx], G[idx], basearray[j], - m, barrett_y, barrett_k, barrett_r1, barrett_r2 ); + mpi_mulm( G[idx], G[idx], basearray[j], m ); } } if( !G[idx] ) G[idx] = mpi_alloc(0); } } - barrett_mulm(res, tmp, G[idx], m, barrett_y, barrett_k, barrett_r1, barrett_r2 ); + mpi_mulm(res, tmp, G[idx], m ); } /* cleanup */ mpi_free(tmp); - #ifdef USE_BARRETT - mpi_free(barrett_y); - mpi_free(barrett_r1); - mpi_free(barrett_r2); - #endif for(i=0; i < (1<<k); i++ ) mpi_free(G[i]); m_free(G); } - -#ifdef USE_BARRETT -static void -barrett_mulm( MPI w, MPI u, MPI v, MPI m, MPI y, int k, MPI r1, MPI r2 ) -{ - mpi_mul(w, u, v); - if( calc_barrett( w, w, m, y, k, r1, r2 ) ) - mpi_fdiv_r( w, w, m ); -} - -/**************** - * Barrett precalculation: y = floor(b^(2k) / m) - */ -static MPI -init_barrett( MPI m, int *k, MPI *r1, MPI *r2 ) -{ - MPI tmp; - - mpi_normalize( m ); - *k = mpi_get_nlimbs( m ); - tmp = mpi_alloc( *k + 1 ); - mpi_set_ui( tmp, 1 ); - mpi_lshift_limbs( tmp, 2 * *k ); - mpi_fdiv_q( tmp, tmp, m ); - *r1 = mpi_alloc( 2* *k + 1 ); - *r2 = mpi_alloc( 2* *k + 1 ); - return tmp; -} - -/**************** - * Barrett reduction: We assume that these conditions are met: - * Given x =(x_2k-1 ...x_0)_b - * m =(m_k-1 ....m_0)_b with m_k-1 != 0 - * Output r = x mod m - * Before using this function init_barret must be used to calucalte y and k. - * Returns: false = no error - * true = can't perform barret reduction - */ -static int -calc_barrett( MPI r, MPI x, MPI m, MPI y, int k, MPI r1, MPI r2 ) -{ - int xx = k > 3 ? k-3:0; - - mpi_normalize( x ); - if( mpi_get_nlimbs(x) > 2*k ) - return 1; /* can't do it */ - - /* 1. q1 = floor( x / b^k-1) - * q2 = q1 * y - * q3 = floor( q2 / b^k+1 ) - * Actually, we don't need qx, we can work direct on r2 - */ - mpi_set( r2, x ); - mpi_rshift_limbs( r2, k-1 ); - mpi_mul( r2, r2, y ); - mpi_rshift_limbs( r2, k+1 ); - - /* 2. r1 = x mod b^k+1 - * r2 = q3 * m mod b^k+1 - * r = r1 - r2 - * 3. if r < 0 then r = r + b^k+1 - */ - mpi_set( r1, x ); - if( r1->nlimbs > k+1 ) /* quick modulo operation */ - r1->nlimbs = k+1; - mpi_mul( r2, r2, m ); - if( r2->nlimbs > k+1 ) /* quick modulo operation */ - r2->nlimbs = k+1; - mpi_sub( r, r1, r2 ); - - if( mpi_is_neg( r ) ) { - MPI tmp; - - tmp = mpi_alloc( k + 2 ); - mpi_set_ui( tmp, 1 ); - mpi_lshift_limbs( tmp, k+1 ); - mpi_add( r, r, tmp ); - mpi_free(tmp); - } - - /* 4. while r >= m do r = r - m */ - while( mpi_cmp( r, m ) >= 0 ) - mpi_sub( r, r, m ); - - return 0; -} -#endif /* USE_BARRETT */ - |