Function test_ecmult_multi_random

src/secp256k1/src/tests.c:5009–5173

}

static int test_ecmult_multi_random(secp256k1_scratch *scratch) {
    /* Large random test for ecmult_multi_* functions which exercises:
     * - Few or many inputs (0 up to 128, roughly exponentially distributed).
     * - Few or many 0*P or a*INF inputs (roughly uniformly distributed).
     * - Including or excluding an nonzero a*G term (or such a term at all).
     * - Final expected result equal to infinity or not (roughly 50%).
     * - ecmult_multi_var, ecmult_strauss_single_batch, ecmult_pippenger_single_batch
     */

    /* These 4 variables define the eventual input to the ecmult_multi function.
     * g_scalar is the G scalar fed to it (or NULL, possibly, if g_scalar=0), and
     * scalars[0..filled-1] and gejs[0..filled-1] are the scalars and points
     * which form its normal inputs. */
    int filled = 0;
    secp256k1_scalar g_scalar = SECP256K1_SCALAR_CONST(0, 0, 0, 0, 0, 0, 0, 0);
    secp256k1_scalar scalars[128];
    secp256k1_gej gejs[128];
    /* The expected result, and the computed result. */
    secp256k1_gej expected, computed;
    /* Temporaries. */
    secp256k1_scalar sc_tmp;
    secp256k1_ge ge_tmp;
    /* Variables needed for the actual input to ecmult_multi. */
    secp256k1_ge ges[128];
    ecmult_multi_data data;

    int i;
    /* Which multiplication function to use */
    int fn = secp256k1_testrand_int(3);
    secp256k1_ecmult_multi_func ecmult_multi = fn == 0 ? secp256k1_ecmult_multi_var :
                                               fn == 1 ? secp256k1_ecmult_strauss_batch_single :
                                               secp256k1_ecmult_pippenger_batch_single;
    /* Simulate exponentially distributed num. */
    int num_bits = 2 + secp256k1_testrand_int(6);
    /* Number of (scalar, point) inputs (excluding g). */
    int num = secp256k1_testrand_int((1 << num_bits) + 1);
    /* Number of those which are nonzero. */
    int num_nonzero = secp256k1_testrand_int(num + 1);
    /* Whether we're aiming to create an input with nonzero expected result. */
    int nonzero_result = secp256k1_testrand_bits(1);
    /* Whether we will provide nonzero g multiplicand. In some cases our hand
     * is forced here based on num_nonzero and nonzero_result. */
    int g_nonzero = num_nonzero == 0 ? nonzero_result :
                    num_nonzero == 1 && !nonzero_result ? 1 :
                    (int)secp256k1_testrand_bits(1);
    /* Which g_scalar pointer to pass into ecmult_multi(). */
    const secp256k1_scalar* g_scalar_ptr = (g_nonzero || secp256k1_testrand_bits(1)) ? &g_scalar : NULL;
    /* How many EC multiplications were performed in this function. */
    int mults = 0;
    /* How many randomization steps to apply to the input list. */
    int rands = (int)secp256k1_testrand_bits(3);
    if (rands > num_nonzero) rands = num_nonzero;

    secp256k1_gej_set_infinity(&expected);
    secp256k1_gej_set_infinity(&gejs[0]);
    secp256k1_scalar_set_int(&scalars[0], 0);

    if (g_nonzero) {