From 35d6d46169717d60f3f8728d0b6df0cfbd57e056 Mon Sep 17 00:00:00 2001 From: Alexander K Date: Thu, 31 Oct 2019 14:46:45 +0300 Subject: [PATCH] Small performance improvement of mbedtls_mpi_div_mpi(): 1. don't use dynamic allocator for fixed size T2; 2. move T2 initialization out of the inner loop. --- library/bignum.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/library/bignum.c b/library/bignum.c index d5bde8b2c..faf2be6e7 100644 --- a/library/bignum.c +++ b/library/bignum.c @@ -1632,6 +1632,7 @@ int mbedtls_mpi_div_mpi( mbedtls_mpi *Q, mbedtls_mpi *R, const mbedtls_mpi *A, int ret; size_t i, n, t, k; mbedtls_mpi X, Y, Z, T1, T2; + mbedtls_mpi_uint __tp2[3]; MPI_VALIDATE_RET( A != NULL ); MPI_VALIDATE_RET( B != NULL ); @@ -1639,7 +1640,11 @@ int mbedtls_mpi_div_mpi( mbedtls_mpi *Q, mbedtls_mpi *R, const mbedtls_mpi *A, return( MBEDTLS_ERR_MPI_DIVISION_BY_ZERO ); mbedtls_mpi_init( &X ); mbedtls_mpi_init( &Y ); mbedtls_mpi_init( &Z ); - mbedtls_mpi_init( &T1 ); mbedtls_mpi_init( &T2 ); + mbedtls_mpi_init( &T1 ); + /* Avoid dynamic memory allocations for constant-size T2. */ + T2.s = 1; + T2.n = 3; + T2.p = __tp2; if( mbedtls_mpi_cmp_abs( A, B ) < 0 ) { @@ -1655,7 +1660,6 @@ int mbedtls_mpi_div_mpi( mbedtls_mpi *Q, mbedtls_mpi *R, const mbedtls_mpi *A, MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &Z, A->n + 2 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &Z, 0 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &T1, 2 ) ); - MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &T2, 3 ) ); k = mbedtls_mpi_bitlen( &Y ) % biL; if( k < biL - 1 ) @@ -1687,6 +1691,10 @@ int mbedtls_mpi_div_mpi( mbedtls_mpi *Q, mbedtls_mpi *R, const mbedtls_mpi *A, Y.p[t], NULL); } + T2.p[0] = ( i < 2 ) ? 0 : X.p[i - 2]; + T2.p[1] = ( i < 1 ) ? 0 : X.p[i - 1]; + T2.p[2] = X.p[i]; + Z.p[i - t - 1]++; do { @@ -1696,11 +1704,6 @@ int mbedtls_mpi_div_mpi( mbedtls_mpi *Q, mbedtls_mpi *R, const mbedtls_mpi *A, T1.p[0] = ( t < 1 ) ? 0 : Y.p[t - 1]; T1.p[1] = Y.p[t]; MBEDTLS_MPI_CHK( mbedtls_mpi_mul_int( &T1, &T1, Z.p[i - t - 1] ) ); - - MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &T2, 0 ) ); - T2.p[0] = ( i < 2 ) ? 0 : X.p[i - 2]; - T2.p[1] = ( i < 1 ) ? 0 : X.p[i - 1]; - T2.p[2] = X.p[i]; } while( mbedtls_mpi_cmp_mpi( &T1, &T2 ) > 0 ); @@ -1736,7 +1739,7 @@ int mbedtls_mpi_div_mpi( mbedtls_mpi *Q, mbedtls_mpi *R, const mbedtls_mpi *A, cleanup: mbedtls_mpi_free( &X ); mbedtls_mpi_free( &Y ); mbedtls_mpi_free( &Z ); - mbedtls_mpi_free( &T1 ); mbedtls_mpi_free( &T2 ); + mbedtls_mpi_free( &T1 ); return( ret ); }