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feat: add vim.str_utf_{start,end} (#16129)

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vim.str_utf_{start,end} return the offset from the current position to
the start and end of the current utf-character (nearest codepoint)
respectively.
This commit is contained in:
Michael Lingelbach
2021-10-30 10:30:40 -07:00
committed by GitHub
parent 97ae0ab4d8
commit 2230b578d1
3 changed files with 104 additions and 0 deletions
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34
src/nvim/mbyte.c
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@@ -1883,6 +1883,40 @@ int mb_tail_off(char_u *base, char_u *p)
return i;
}
/// Return the offset from "p" to the first byte of the character it points
/// into. Can start anywhere in a stream of bytes.
///
/// @param[in] base Pointer to start of string
/// @param[in] p Pointer to byte for which to return the offset to the previous codepoint
//
/// @return 0 if invalid sequence, else offset to previous codepoint
int mb_head_off(char_u *base, char_u *p)
{
int i;
int j;
if (*p == NUL) {
return 0;
}
// Find the first character that is not 10xx.xxxx
for (i = 0; p - i > base; i--) {
if ((p[i] & 0xc0) != 0x80) {
break;
}
}
// Find the last character that is 10xx.xxxx
for (j = 0; (p[j + 1] & 0xc0) == 0x80; j++) {}
// Check for illegal sequence.
if (utf8len_tab[p[i]] == 1) {
return 0;
}
return i;
}
/*
* Find the next illegal byte sequence.
*/