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Make the string cursor able to run backwards as well as forwards

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Daphne Preston-Kendal 2021-12-11 11:43:23 +01:00
parent 4e0f10ad21
commit a746370431
1 changed files with 21 additions and 3 deletions
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20
sexp.c
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@ -1260,6 +1260,9 @@ sexp sexp_string_index_to_cursor (sexp ctx, sexp self, sexp_sint_t n, sexp str,
sexp cursor;
sexp_sint_t i, j, limit;
unsigned char *p;
#if SEXP_USE_STRING_REF_CACHE
unsigned char *q;
#endif
sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, index);
p = (unsigned char*)sexp_string_data(str);
@ -1277,13 +1280,28 @@ sexp sexp_string_index_to_cursor (sexp ctx, sexp self, sexp_sint_t n, sexp str,
}
}
#elif SEXP_USE_STRING_REF_CACHE
if (i >= sexp_cached_char_idx(str)) {
if (i > (sexp_cached_char_idx(str) + ((sexp_string_length(str) - sexp_cached_char_idx(str)) >> 1))) {
j = sexp_string_size(str);
i = -(sexp_string_length(str) - i);
} else if (i > (sexp_cached_char_idx(str) >> 1)) {
j = sexp_unbox_string_cursor(sexp_cached_cursor(str));
i -= sexp_cached_char_idx(str);
}
#endif
#if SEXP_USE_STRING_REF_CACHE
if (i >= 0) {
#endif
for ( ; i>0 && j<limit; i--)
j += sexp_utf8_initial_byte_count(p[j]);
#if SEXP_USE_STRING_REF_CACHE
} else {
for (q=p+j; i<0 && q>=p; i++)
q = (unsigned char*)sexp_string_utf8_prev(q);
j = q - p;
}
#endif
if (i != 0)
return sexp_user_exception(ctx, self, "string-index->cursor: index out of range", index);
cursor = sexp_make_string_cursor(j);