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See ChangeLog: Fri Jul 2 11:45:54 CEST 1999 Werner Koch
This commit is contained in:
Werner Koch
parent
28eb86c006
commit
86abac78a2
15 changed files with 366 additions and 64 deletions
141
mpi/mpi-mpow.c
141
mpi/mpi-mpow.c
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@ -1,5 +1,5 @@
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/* mpi-mpow.c - MPI functions
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* Copyright (C) 1998 Free Software Foundation, Inc.
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* Copyright (C) 1998, 1999 Free Software Foundation, Inc.
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*
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* This file is part of GnuPG.
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*
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@ -25,6 +25,22 @@
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#include "longlong.h"
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#include <assert.h>
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/* Barrett is slower than the classical way. It can be tweaked by
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* using partial multiplications
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*/
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/*#define USE_BARRETT*/
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#ifdef USE_BARRETT
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static void barrett_mulm( MPI w, MPI u, MPI v, MPI m, MPI y, int k, MPI r1, MPI r2 );
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static MPI init_barrett( MPI m, int *k, MPI *r1, MPI *r2 );
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static int calc_barrett( MPI r, MPI x, MPI m, MPI y, int k, MPI r1, MPI r2 );
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#else
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#define barrett_mulm( w, u, v, m, y, k, r1, r2 ) mpi_mulm( (w), (u), (v), (m) )
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#endif
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static int
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build_index( MPI *exparray, int k, int i, int t )
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{
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@ -52,6 +68,10 @@ mpi_mulpowm( MPI res, MPI *basearray, MPI *exparray, MPI m)
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int i, j, idx;
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MPI *G; /* table with precomputed values of size 2^k */
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MPI tmp;
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#ifdef USE_BARRETT
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MPI barrett_y, barrett_r1, barrett_r2;
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int barrett_k;
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#endif
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for(k=0; basearray[k]; k++ )
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;
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@ -68,27 +88,15 @@ mpi_mulpowm( MPI res, MPI *basearray, MPI *exparray, MPI m)
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assert( k < 10 );
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G = m_alloc_clear( (1<<k) * sizeof *G );
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#if 0
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/* do the precomputation */
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G[0] = mpi_alloc_set_ui( 1 );
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for(i=1; i < (1<<k); i++ ) {
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for(j=0; j < k; j++ ) {
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if( (i & (1<<j) ) ) {
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if( !G[i] )
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G[i] = mpi_copy( basearray[j] );
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else
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mpi_mulm( G[i], G[i], basearray[j], m );
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}
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}
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if( !G[i] )
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G[i] = mpi_alloc(0);
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}
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#ifdef USE_BARRETT
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barrett_y = init_barrett( m, &barrett_k, &barrett_r1, &barrett_r2 );
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#endif
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/* and calculate */
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tmp = mpi_alloc( mpi_get_nlimbs(m)+1 );
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mpi_set_ui( res, 1 );
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for(i = 1; i <= t; i++ ) {
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mpi_mulm(tmp, res, res, m );
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barrett_mulm(tmp, res, res, m, barrett_y, barrett_k,
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barrett_r1, barrett_r2 );
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idx = build_index( exparray, k, i, t );
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assert( idx >= 0 && idx < (1<<k) );
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if( !G[idx] ) {
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@ -100,20 +108,115 @@ mpi_mulpowm( MPI res, MPI *basearray, MPI *exparray, MPI m)
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if( !G[idx] )
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G[idx] = mpi_copy( basearray[j] );
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else
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mpi_mulm( G[idx], G[idx], basearray[j], m );
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barrett_mulm( G[idx], G[idx], basearray[j],
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m, barrett_y, barrett_k, barrett_r1, barrett_r2 );
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}
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}
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if( !G[idx] )
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G[idx] = mpi_alloc(0);
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}
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}
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mpi_mulm(res, tmp, G[idx], m );
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barrett_mulm(res, tmp, G[idx], m, barrett_y, barrett_k, barrett_r1, barrett_r2 );
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}
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/* cleanup */
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mpi_free(tmp);
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#ifdef USE_BARRETT
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mpi_free(barrett_y);
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mpi_free(barrett_r1);
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mpi_free(barrett_r2);
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#endif
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for(i=0; i < (1<<k); i++ )
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mpi_free(G[i]);
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m_free(G);
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}
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#ifdef USE_BARRETT
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static void
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barrett_mulm( MPI w, MPI u, MPI v, MPI m, MPI y, int k, MPI r1, MPI r2 )
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{
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mpi_mul(w, u, v);
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if( calc_barrett( w, w, m, y, k, r1, r2 ) )
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mpi_fdiv_r( w, w, m );
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}
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/****************
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* Barrett precalculation: y = floor(b^(2k) / m)
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*/
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static MPI
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init_barrett( MPI m, int *k, MPI *r1, MPI *r2 )
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{
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MPI tmp;
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mpi_normalize( m );
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*k = mpi_get_nlimbs( m );
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tmp = mpi_alloc( *k + 1 );
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mpi_set_ui( tmp, 1 );
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mpi_lshift_limbs( tmp, 2 * *k );
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mpi_fdiv_q( tmp, tmp, m );
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*r1 = mpi_alloc( 2* *k + 1 );
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*r2 = mpi_alloc( 2* *k + 1 );
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return tmp;
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}
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/****************
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* Barrett reduction: We assume that these conditions are met:
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* Given x =(x_2k-1 ...x_0)_b
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* m =(m_k-1 ....m_0)_b with m_k-1 != 0
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* Output r = x mod m
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* Before using this function init_barret must be used to calucalte y and k.
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* Returns: false = no error
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* true = can't perform barret reduction
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*/
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static int
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calc_barrett( MPI r, MPI x, MPI m, MPI y, int k, MPI r1, MPI r2 )
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{
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int xx = k > 3 ? k-3:0;
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mpi_normalize( x );
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if( mpi_get_nlimbs(x) > 2*k )
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return 1; /* can't do it */
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/* 1. q1 = floor( x / b^k-1)
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* q2 = q1 * y
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* q3 = floor( q2 / b^k+1 )
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* Actually, we don't need qx, we can work direct on r2
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*/
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mpi_set( r2, x );
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mpi_rshift_limbs( r2, k-1 );
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mpi_mul( r2, r2, y );
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mpi_rshift_limbs( r2, k+1 );
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/* 2. r1 = x mod b^k+1
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* r2 = q3 * m mod b^k+1
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* r = r1 - r2
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* 3. if r < 0 then r = r + b^k+1
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*/
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mpi_set( r1, x );
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if( r1->nlimbs > k+1 ) /* quick modulo operation */
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r1->nlimbs = k+1;
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mpi_mul( r2, r2, m );
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if( r2->nlimbs > k+1 ) /* quick modulo operation */
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r2->nlimbs = k+1;
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mpi_sub( r, r1, r2 );
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if( mpi_is_neg( r ) ) {
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MPI tmp;
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tmp = mpi_alloc( k + 2 );
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mpi_set_ui( tmp, 1 );
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mpi_lshift_limbs( tmp, k+1 );
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mpi_add( r, r, tmp );
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mpi_free(tmp);
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}
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/* 4. while r >= m do r = r - m */
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while( mpi_cmp( r, m ) >= 0 )
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mpi_sub( r, r, m );
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return 0;
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}
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#endif /* USE_BARRETT */
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