static unsigned int BN_STACK_pop(BN_STACK *st)
{
    return st->indexes[--(st->depth)];
}
['int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,\n                            const EC_POINT *pub_key, const EC_KEY *ecdh)\n{\n    BN_CTX *ctx;\n    EC_POINT *tmp = NULL;\n    BIGNUM *x = NULL;\n    const BIGNUM *priv_key;\n    const EC_GROUP *group;\n    int ret = 0;\n    size_t buflen, len;\n    unsigned char *buf = NULL;\n    if ((ctx = BN_CTX_new()) == NULL)\n        goto err;\n    BN_CTX_start(ctx);\n    x = BN_CTX_get(ctx);\n    if (x == NULL) {\n        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);\n        goto err;\n    }\n    priv_key = EC_KEY_get0_private_key(ecdh);\n    if (priv_key == NULL) {\n        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_NO_PRIVATE_VALUE);\n        goto err;\n    }\n    group = EC_KEY_get0_group(ecdh);\n    if (EC_KEY_get_flags(ecdh) & EC_FLAG_COFACTOR_ECDH) {\n        if (!EC_GROUP_get_cofactor(group, x, NULL) ||\n            !BN_mul(x, x, priv_key, ctx)) {\n            ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);\n            goto err;\n        }\n        priv_key = x;\n    }\n    if ((tmp = EC_POINT_new(group)) == NULL) {\n        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);\n        goto err;\n    }\n    if (!EC_POINT_mul(group, tmp, NULL, pub_key, priv_key, ctx)) {\n        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);\n        goto err;\n    }\n    if (EC_METHOD_get_field_type(EC_GROUP_method_of(group)) ==\n        NID_X9_62_prime_field) {\n        if (!EC_POINT_get_affine_coordinates_GFp(group, tmp, x, NULL, ctx)) {\n            ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);\n            goto err;\n        }\n    }\n#ifndef OPENSSL_NO_EC2M\n    else {\n        if (!EC_POINT_get_affine_coordinates_GF2m(group, tmp, x, NULL, ctx)) {\n            ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);\n            goto err;\n        }\n    }\n#endif\n    buflen = (EC_GROUP_get_degree(group) + 7) / 8;\n    len = BN_num_bytes(x);\n    if (len > buflen) {\n        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_INTERNAL_ERROR);\n        goto err;\n    }\n    if ((buf = OPENSSL_malloc(buflen)) == NULL) {\n        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);\n        goto err;\n    }\n    memset(buf, 0, buflen - len);\n    if (len != (size_t)BN_bn2bin(x, buf + buflen - len)) {\n        ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_BN_LIB);\n        goto err;\n    }\n    *pout = buf;\n    *poutlen = buflen;\n    buf = NULL;\n    ret = 1;\n err:\n    EC_POINT_free(tmp);\n    if (ctx)\n        BN_CTX_end(ctx);\n    BN_CTX_free(ctx);\n    OPENSSL_free(buf);\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}', '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}']