ENGINES: Optimize string handling

[mikrosk]

[v]snprintf() / [v]fprintf() used in String::format() gets called roughly a million times (!) when adding a game.

Reducing the number of calls into libc leads to about 10% speed improvement on the atari backend (which is counting in seconds!)

I wish I could get rid of that Common::String::format("%d", _md5Bytes); construct, too. But even in its present form (i.e. with just reduced content passed to String::format) it leads to a measurable speed-up.

[sev-]

Could you try using itoa() here and see if it is any faster?

[mikrosk]

itoa is a non-standard function. However out of curiosity I have tried std::to_string and my custom itoa:

• Common::String::format: 74.290s
• std::to_string: 73.440s
• my own itoa: 73.070s

static Common::String itoa(uint val)
{
	Common::String s;

	do
	{
		uint a = val % 10;
		val /= 10;

		s += a + '0';

	} while (val > 0);

	if (s.size() > 1) {
		int start = 0 , end = s.size()-1;
		while (start < end) {
			auto temp = s[start];
			s.setChar(s[end], start);
			s.setChar(temp, end);
			start += 1;
			end -= 1;
		}
	}

	return s;
}

So there is some speedup but not that significant.

[lephilousophe]

Currently it's not an itoa but more an utoa.
I think this could go into BaseString class.

[sev-]

Yes, that would be nice to have in the base string class. Just to my surprise, the code formatting is off.

[mikrosk]

So if I implemented BaseString::itoa() (which would handle also negative numbers), would you accept it?

[sev-]

Merging, thanks!