Add startsWith function to HGS language

[holstvoogd]

I'm creating a config for a Butterstick board & needed a way to neatly customize some constraints for all ports starting with some prefix.

Example of how I use it:

func pin(name, pin) {
    io_type := "LVCMOS33";
    misc := "";

    if ( startsWith(name, "user_btn") ) { io_type = "SSTL135_I"; }
    if ( startsWith(name, "ulpi_") ) { io_type = "LVCMOS18"; misc="SLEWRATE=FAST"; }
    if ( name = "rst_n" ) { misc = "OPENDRAIN=ON"; }

    config := "LOCATE COMP \""+ name + "\" SITE \""+ pin +"\";";
    config = config + "\nIOBUF PORT \""+ name + "\" IO_TYPE=" + io_type + " " + misc + ";";

    if (name = "clk30") { config = config + "\nFREQUENCY PORT \"clk30\" 30.0 MHz;"; }

    return config + "\n";
}
for (i:=0; i<sizeOf(model.ports); i++) {
    port:=model.ports[i];
    if (port.bits=1) {
        println(pin(port.name, port.pin));
    } else {
        pins := splitString(port.pin);
        for (p:=0;p<sizeOf(pins);p++) {
          println(pin(port.name + "[" + p + "]", pins[p]));
        }
    }
}

It builds & verifies. And I've confirmed it works for generating my constraints file.

Since it seems most trivial functions are not explicitly tested, I didn't add one for this either. Let me know if I should add one though!

[codecov-commenter]

Codecov Report

Merging #994 (3e8f43c) into master (e46b2bd) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff            @@
##             master    #994   +/-   ##
========================================
  Coverage      56.6%   56.6%           
- Complexity     6553    6554    +1     
========================================
  Files           679     679           
  Lines         35358   35359    +1     
  Branches       4761    4761           
========================================
+ Hits          20042   20043    +1     
  Misses        14111   14111           
  Partials       1205    1205           

Impacted Files	Coverage Δ
.../main/java/de/neemann/digital/hdl/hgs/Context.java	79.5% <100.0%> (+<0.1%)	⬆️

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