Convert Protocol names to shared text

[crankyoldgit]

• Reduce string duplication by centralising protocol text.
• Use a single array (double null terminated string) to store the text
  • Allows for much simpler, & more compact code.
  • Kudos to @s-hadinger for the idea.
• Saves about ~3.8 kbytes.

FYI @s-hadinger

[s-hadinger]

Thanks David. I'm surprised that strcasecmp accepts PROGMEM parameter without crashing. Shouldn't you use strcasecmp_P instead?

Theo has a nice trick to save even more. In a nutshell, concatenate all strings of a specific type to a single string separate with |:

const PROGMEM char[] kDecodeTypeStr = "|"  kUnknownStr "|" kUnusedStr
             "|" kAirwellStr "|" kAiwaRcT501Str ; // and so on...

Then create an array of codes in parallel of the strings with the same indices:

const PROGMEM uint8_t[] kDecodeTypeCodes = { decode_type_t::UNKNOWN, decode_type_t::UNUSED,
             decode_type_t::AIRWELL, decode_type_t::AIWA_RC_T501,
             };  // and so on

Use the following for index to text (note the first string before the first | is a common prefix to all other strings, so leave it empty):

char* GetTextIndexed(char* destination, size_t destination_size, uint32_t index, const char* haystack)
{
  // Returns empty string if not found
  // Returns text of found
  char* write = destination;
  const char* read = haystack;

  index++;
  while (index--) {
    size_t size = destination_size -1;
    write = destination;
    char ch = '.';
    while ((ch != '\0') && (ch != '|')) {
      ch = pgm_read_byte(read++);
      if (size && (ch != '|'))  {
        *write++ = ch;
        size--;
      }
    }
    if (0 == ch) {
      if (index) {
        write = destination;
      }
      break;
    }
  }
  *write = '\0';
  return destination;
}

You can then have a strategy for matching similar to this one:

bool DecodeCommand(const char* haystack, void (* const MyCommand[])(void))
{
  GetTextIndexed(XdrvMailbox.command, CMDSZ, 0, haystack);  // Get prefix if available
  int prefix_length = strlen(XdrvMailbox.command);
  if (prefix_length) {
    char prefix[prefix_length +1];
    snprintf_P(prefix, sizeof(prefix), XdrvMailbox.topic);  // Copy prefix part only
    if (strcasecmp(prefix, XdrvMailbox.command)) {
      return false;                                         // Prefix not in command
    }
  }

   // retrieve the actual code from kDecodeTypeCodes
    return true;
  }
  return false;
}

The magic is that it works backwards, scan kDecodeTypeCodes for code to string, and use a first match to choose your preferred string in case a single code matches multiple strings.

This should save you a lot of code :)

[crankyoldgit]

@s-hadinger Thanks. I'll take a look at doing just that.

[crankyoldgit]

I'm surprised that strcasecmp accepts PROGMEM parameter without crashing. Shouldn't you use strcasecmp_P instead?

Interestingly, I tried using strcasecmp_P just now (I'm finally getting to this), and it added 500+ bytes to the binary size. So, if it ain't broke .. don't fix it?! /shrug.

[crankyoldgit]

This should save you a lot of code :)

@s-hadinger It did. I did something simpler as I don't have the same issues as Tasmota. I could do what you guys do, and shave a few more bytes, but this way makes the code more readable.
Anyway. Total saving is now approx 2.3k.

[crankyoldgit]

Another revision, this time removing redundant strings, & using a single double "null terminated" string to store the text. All in all, an additional 1.5k more saving.

[s-hadinger]

Wow. Great job. Let me try it in Tasmota

[s-hadinger]

I confirm it's working on Tasmota, no crash due to PROGMEM.

It saves 3.4KB of flash. Do you plan to release a version v2.7.6 with the space saving feature?

[crankyoldgit]

Do you plan to release a version v2.7.6 with the space saving feature?

Yes, eventually.

[crankyoldgit]

7 days have passed. No un-addressed negative feedback. Merging.