
< uint32_t payload_size;
< payload_size = smh->submessageLength -
---
> uint32_t payload_size;
> uint32_t to_subtract = /* other value */;
> if (smh->submessageLength < to_subtract) {
>     // Handle error condition
>     return false;
> }
> payload_size = smh->submessageLength - to_subtract;
