On Fri, Sep 02, 2022 at 02:08:03PM -0300, atrtar...@cock.li wrote:
> Quite inefficient really, but I guess it's fine since my usage would be
> only user input (left arrow)
If efficiency is not a concern, then you can easily use something like
this (just a quick prototype, didn't verify if it's correct or not):
/* returns an offset into `s` */
static size_t
prev_char_offset(const char *s, size_t slen, size_t off)
{
assert(s != NULL);
assert(slen > 0);
assert(off <= slen);
size_t ret = 0;
const char *const end = s + slen;
while (s < end) {
size_t n = grapheme_next_character_break_utf8(s, end -
s);
if (ret + n >= off)
return ret;
ret += n;
s += n;
}
return 0; /* unreachable (?) */
}
If I was expecting a decent amount of non-ascii input, I would use the
bitvector approach described by Thomas Oltmann. 1bit per byte overhead
should be fine for most use-cases.
- NRK
