static unsigned int BN_STACK_pop(BN_STACK *st)
{
    return st->indexes[--(st->depth)];
}
['static int test_gf2m_modexp(void)\n{\n    BIGNUM *a = NULL, *b[2] = {NULL,NULL}, *c = NULL, *d = NULL;\n    BIGNUM *e = NULL, *f = NULL;\n    int i, j, st = 0;\n    if (!TEST_ptr(a = BN_new())\n            || !TEST_ptr(b[0] = BN_new())\n            || !TEST_ptr(b[1] = BN_new())\n            || !TEST_ptr(c = BN_new())\n            || !TEST_ptr(d = BN_new())\n            || !TEST_ptr(e = BN_new())\n            || !TEST_ptr(f = BN_new()))\n        goto err;\n    BN_GF2m_arr2poly(p0, b[0]);\n    BN_GF2m_arr2poly(p1, b[1]);\n    for (i = 0; i < NUM0; i++) {\n        BN_bntest_rand(a, 512, 0, 0);\n        BN_bntest_rand(c, 512, 0, 0);\n        BN_bntest_rand(d, 512, 0, 0);\n        for (j = 0; j < 2; j++) {\n            BN_GF2m_mod_exp(e, a, c, b[j], ctx);\n            BN_GF2m_mod_exp(f, a, d, b[j], ctx);\n            BN_GF2m_mod_mul(e, e, f, b[j], ctx);\n            BN_add(f, c, d);\n            BN_GF2m_mod_exp(f, a, f, b[j], ctx);\n            BN_GF2m_add(f, e, f);\n            if (!TEST_BN_eq_zero(f))\n                goto err;\n        }\n    }\n    st = 1;\n err:\n    BN_free(a);\n    BN_free(b[0]);\n    BN_free(b[1]);\n    BN_free(c);\n    BN_free(d);\n    BN_free(e);\n    BN_free(f);\n    return st;\n}', 'int BN_GF2m_mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,\n                    const BIGNUM *p, BN_CTX *ctx)\n{\n    int ret = 0;\n    const int max = BN_num_bits(p) + 1;\n    int *arr = NULL;\n    bn_check_top(a);\n    bn_check_top(b);\n    bn_check_top(p);\n    if ((arr = OPENSSL_malloc(sizeof(*arr) * max)) == NULL)\n        goto err;\n    ret = BN_GF2m_poly2arr(p, arr, max);\n    if (!ret || ret > max) {\n        BNerr(BN_F_BN_GF2M_MOD_EXP, BN_R_INVALID_LENGTH);\n        goto err;\n    }\n    ret = BN_GF2m_mod_exp_arr(r, a, b, arr, ctx);\n    bn_check_top(r);\n err:\n    OPENSSL_free(arr);\n    return ret;\n}', 'int BN_GF2m_mod_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,\n                    const BIGNUM *p, BN_CTX *ctx)\n{\n    int ret = 0;\n    const int max = BN_num_bits(p) + 1;\n    int *arr = NULL;\n    bn_check_top(a);\n    bn_check_top(b);\n    bn_check_top(p);\n    if ((arr = OPENSSL_malloc(sizeof(*arr) * max)) == NULL)\n        goto err;\n    ret = BN_GF2m_poly2arr(p, arr, max);\n    if (!ret || ret > max) {\n        BNerr(BN_F_BN_GF2M_MOD_MUL, BN_R_INVALID_LENGTH);\n        goto err;\n    }\n    ret = BN_GF2m_mod_mul_arr(r, a, b, arr, ctx);\n    bn_check_top(r);\n err:\n    OPENSSL_free(arr);\n    return ret;\n}', 'int BN_GF2m_mod_mul_arr(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,\n                        const int p[], BN_CTX *ctx)\n{\n    int zlen, i, j, k, ret = 0;\n    BIGNUM *s;\n    BN_ULONG x1, x0, y1, y0, zz[4];\n    bn_check_top(a);\n    bn_check_top(b);\n    if (a == b) {\n        return BN_GF2m_mod_sqr_arr(r, a, p, ctx);\n    }\n    BN_CTX_start(ctx);\n    if ((s = BN_CTX_get(ctx)) == NULL)\n        goto err;\n    zlen = a->top + b->top + 4;\n    if (!bn_wexpand(s, zlen))\n        goto err;\n    s->top = zlen;\n    for (i = 0; i < zlen; i++)\n        s->d[i] = 0;\n    for (j = 0; j < b->top; j += 2) {\n        y0 = b->d[j];\n        y1 = ((j + 1) == b->top) ? 0 : b->d[j + 1];\n        for (i = 0; i < a->top; i += 2) {\n            x0 = a->d[i];\n            x1 = ((i + 1) == a->top) ? 0 : a->d[i + 1];\n            bn_GF2m_mul_2x2(zz, x1, x0, y1, y0);\n            for (k = 0; k < 4; k++)\n                s->d[i + j + k] ^= zz[k];\n        }\n    }\n    bn_correct_top(s);\n    if (BN_GF2m_mod_arr(r, s, p))\n        ret = 1;\n    bn_check_top(r);\n err:\n    BN_CTX_end(ctx);\n    return ret;\n}', 'void BN_CTX_start(BN_CTX *ctx)\n{\n    CTXDBG("ENTER BN_CTX_start()", ctx);\n    if (ctx->err_stack || ctx->too_many)\n        ctx->err_stack++;\n    else if (!BN_STACK_push(&ctx->stack, ctx->used)) {\n        BNerr(BN_F_BN_CTX_START, BN_R_TOO_MANY_TEMPORARY_VARIABLES);\n        ctx->err_stack++;\n    }\n    CTXDBG("LEAVE BN_CTX_start()", ctx);\n}', 'void BN_CTX_end(BN_CTX *ctx)\n{\n    CTXDBG("ENTER BN_CTX_end()", ctx);\n    if (ctx->err_stack)\n        ctx->err_stack--;\n    else {\n        unsigned int fp = BN_STACK_pop(&ctx->stack);\n        if (fp < ctx->used)\n            BN_POOL_release(&ctx->pool, ctx->used - fp);\n        ctx->used = fp;\n        ctx->too_many = 0;\n    }\n    CTXDBG("LEAVE BN_CTX_end()", ctx);\n}', 'static unsigned int BN_STACK_pop(BN_STACK *st)\n{\n    return st->indexes[--(st->depth)];\n}']