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feature?: ignored characters `'_ / allowing prefixs 0x and 0b etc... #124
Description
This isn't a performance related feature, but I've found it odd that the charconv spec goes out of its way to avoid parsing what would otherwise be necessary to handle c++'s own floating point literals. What would you think about having some additional utility from_chars like functions to handle those formats?
Ages ago I modified microsoft's charconv to do this for myself, but it broke at some point because headers changed and some utility functions went missing. The core idea is roughly this:
if (fmt is prefixed) {
//bump pointer forward past the prefix for the format
}
//continue parsing like charconv would except skip over specified characters
uint64_t mantissa = 0;
for (;begin != end; ++begin) {
if ((*begin == some_template_pack) || ...)
continue;
const unsigned char digit = char_table[*begin];
if (digit >= base)
break;
//so on...
}Not used your library, but it seems like hex formatted floats have the enum for the format but aren't supported? Could also be the opportunity to add that in.
Activity
lemire commentedon Jan 20, 2022
@Andersama We want the
from_charsfunction to abide by the standard as much as possible. It should be close to a "drop-in" replacement for whatever the standard library provides.However, we also have the
from_chars_advancedfunction which is an extension. There is no limit to what we could do there.Support for other data types and formats is certainly welcome. Please consider providing a pull request, or many pull requests.
Andersama commentedon Feb 9, 2022
It looks like parse_number_string is the underlying function that from_char_advanced is using. Were you expecting the drop in to handle hex floats? Currently it seems like it doesn't, and it seems like I'm about to add a fairly large if / else block otherwise with an extra flag integer to parse_options. Pretty sure that'll be a bit of a performance hit.
lemire commentedon Feb 9, 2022
We have decent benchmarks so we can assess performance issues. I would not necessarily be overly concerned at first.