static unsigned int BN_STACK_pop(BN_STACK *st)
{
    return st->indexes[--(st->depth)];
}
['static int field_tests(const EC_METHOD *meth, const unsigned char *params,\n                       int len)\n{\n    BN_CTX *ctx = NULL;\n    BIGNUM *p = NULL, *a = NULL, *b = NULL;\n    EC_GROUP *group = NULL;\n    int ret = 0;\n    if (!TEST_ptr(ctx = BN_CTX_new()))\n        return 0;\n    BN_CTX_start(ctx);\n    p = BN_CTX_get(ctx);\n    a = BN_CTX_get(ctx);\n    if (!TEST_ptr(b = BN_CTX_get(ctx))\n        || !TEST_ptr(group = EC_GROUP_new(meth))\n        || !TEST_true(BN_bin2bn(params, len, p))\n        || !TEST_true(BN_bin2bn(params + len, len, a))\n        || !TEST_true(BN_bin2bn(params + 2 * len, len, b))\n        || !TEST_true(EC_GROUP_set_curve(group, p, a, b, ctx))\n        || !group_field_tests(group, ctx))\n        goto err;\n    ret = 1;\n err:\n    BN_CTX_end(ctx);\n    BN_CTX_free(ctx);\n    if (group != NULL)\n        EC_GROUP_free(group);\n    return ret;\n}', 'void BN_CTX_start(BN_CTX *ctx)\n{\n    CTXDBG_ENTRY("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_EXIT(ctx);\n}', 'static int group_field_tests(const EC_GROUP *group, BN_CTX *ctx)\n{\n    BIGNUM *a = NULL, *b = NULL, *c = NULL;\n    int ret = 0;\n    if (group->meth->field_inv == NULL || group->meth->field_mul == NULL)\n        return 1;\n    BN_CTX_start(ctx);\n    a = BN_CTX_get(ctx);\n    b = BN_CTX_get(ctx);\n    if (!TEST_ptr(c = BN_CTX_get(ctx))\n        || !TEST_true(group->meth->field_inv(group, b, BN_value_one(), ctx))\n        || !TEST_true(BN_is_one(b))\n        || !TEST_true(BN_pseudo_rand(a, BN_num_bits(group->field) - 1,\n                                     BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY))\n        || !TEST_true(group->meth->field_inv(group, b, a, ctx))\n        || (group->meth->field_encode &&\n            !TEST_true(group->meth->field_encode(group, a, a, ctx)))\n        || (group->meth->field_encode &&\n            !TEST_true(group->meth->field_encode(group, b, b, ctx)))\n        || !TEST_true(group->meth->field_mul(group, c, a, b, ctx))\n        || (group->meth->field_decode &&\n            !TEST_true(group->meth->field_decode(group, c, c, ctx)))\n        || !TEST_true(BN_is_one(c)))\n        goto err;\n    BN_zero(a);\n    if (!TEST_false(group->meth->field_inv(group, b, a, ctx))\n        || !TEST_true(ERR_GET_LIB(ERR_peek_last_error()) == ERR_LIB_EC)\n        || !TEST_true(ERR_GET_REASON(ERR_peek_last_error()) ==\n                      EC_R_CANNOT_INVERT)\n        || !TEST_false(group->meth->field_inv(group, b, group->field, ctx))\n        || !TEST_true(ERR_GET_LIB(ERR_peek_last_error()) == ERR_LIB_EC)\n        || !TEST_true(ERR_GET_REASON(ERR_peek_last_error()) ==\n                      EC_R_CANNOT_INVERT))\n        goto err;\n    ERR_clear_error();\n    ret = 1;\n err:\n    BN_CTX_end(ctx);\n    return ret;\n}', 'void BN_CTX_end(BN_CTX *ctx)\n{\n    CTXDBG_ENTRY("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_EXIT(ctx);\n}', 'static unsigned int BN_STACK_pop(BN_STACK *st)\n{\n    return st->indexes[--(st->depth)];\n}']