diff options
Diffstat (limited to 'mpi/mpi-inv.c')
| -rw-r--r-- | mpi/mpi-inv.c | 103 |
1 files changed, 102 insertions, 1 deletions
diff --git a/mpi/mpi-inv.c b/mpi/mpi-inv.c index 28cde00b6..53ef356b3 100644 --- a/mpi/mpi-inv.c +++ b/mpi/mpi-inv.c @@ -76,7 +76,7 @@ mpi_invm( MPI x, MPI a, MPI n ) mpi_free(t3); mpi_free(u); mpi_free(v); - #else + #elif 0 /* Extended Euclid's algorithm (See TAOPC Vol II, 4.5.2, Alg X) * modified according to Michael Penk's solution for Exercice 35 */ @@ -156,6 +156,107 @@ mpi_invm( MPI x, MPI a, MPI n ) mpi_free(t1); mpi_free(t2); mpi_free(t3); + #else + /* Extended Euclid's algorithm (See TAOPC Vol II, 4.5.2, Alg X) + * modified according to Michael Penk's solution for Exercice 35 + * with further enhancement */ + MPI u, v, u1, u2=NULL, u3, v1, v2=NULL, v3, t1, t2=NULL, t3; + unsigned k; + int sign; + int odd ; + + u = mpi_copy(a); + v = mpi_copy(n); + for(k=0; !mpi_test_bit(u,0) && !mpi_test_bit(v,0); k++ ) { + mpi_rshift(u, u, 1); + mpi_rshift(v, v, 1); + } + odd = mpi_test_bit(v,0); + + u1 = mpi_alloc_set_ui(1); + if( !odd ) + u2 = mpi_alloc_set_ui(0); + u3 = mpi_copy(u); + v1 = mpi_copy(v); + if( !odd ) { + v2 = mpi_alloc( mpi_get_nlimbs(u) ); + mpi_sub( v2, u1, u ); /* U is used as const 1 */ + } + v3 = mpi_copy(v); + if( mpi_test_bit(u, 0) ) { /* u is odd */ + t1 = mpi_alloc_set_ui(0); + if( !odd ) { + t2 = mpi_alloc_set_ui(1); t2->sign = 1; + } + t3 = mpi_copy(v); t3->sign = !t3->sign; + goto Y4; + } + else { + t1 = mpi_alloc_set_ui(1); + if( !odd ) + t2 = mpi_alloc_set_ui(0); + t3 = mpi_copy(u); + } + do { + do { + if( !odd ) { + if( mpi_test_bit(t1, 0) || mpi_test_bit(t2, 0) ) { /* one is odd */ + mpi_add(t1, t1, v); + mpi_sub(t2, t2, u); + } + mpi_rshift(t1, t1, 1); + mpi_rshift(t2, t2, 1); + mpi_rshift(t3, t3, 1); + } + else { + if( mpi_test_bit(t1, 0) ) + mpi_add(t1, t1, v); + mpi_rshift(t1, t1, 1); + mpi_rshift(t3, t3, 1); + } + Y4: + } while( !mpi_test_bit( t3, 0 ) ); /* while t3 is even */ + + if( !t3->sign ) { + mpi_set(u1, t1); + if( !odd ) + mpi_set(u2, t2); + mpi_set(u3, t3); + } + else { + mpi_sub(v1, v, t1); + sign = u->sign; u->sign = !u->sign; + if( !odd ) + mpi_sub(v2, u, t2); + u->sign = sign; + sign = t3->sign; t3->sign = !t3->sign; + mpi_set(v3, t3); + t3->sign = sign; + } + mpi_sub(t1, u1, v1); + if( !odd ) + mpi_sub(t2, u2, v2); + mpi_sub(t3, u3, v3); + if( t1->sign ) { + mpi_add(t1, t1, v); + if( !odd ) + mpi_sub(t2, t2, u); + } + } while( mpi_cmp_ui( t3, 0 ) ); /* while t3 != 0 */ + /* mpi_lshift( u3, k ); */ + mpi_set(x, u1); + + mpi_free(u1); + mpi_free(v1); + mpi_free(t1); + if( !odd ) { + mpi_free(u2); + mpi_free(v2); + mpi_free(t2); + } + mpi_free(u3); + mpi_free(v3); + mpi_free(t3); #endif } |