2@ = strlen 0@
3@ = strlen 1@
memcpy(0@ + 2@, 1@, 3@)
memset(0@ + 2@ + 3@, 0, 1) // null char
tested , works perfect.
:strcat
// 0@ - destination, 1@ - source
// Example: 0AB1: @strcat 2 destination 0@ source 1@
0AB1: @strlen 1 string 0@ _return: 2@
0AB1: @strlen 1 string 1@ _return: 3@...