ASC converts full-width katakana and ASCII characters to half-width equivalent characters, copying all others.
The distinction between half-width and full-width characters is described in http://www.unicode.org/reports/tr11/.
While in obsolete encodings ASC used to translate between 2-byte and 1-byte characters, this is not the case in UTF-8.
For most strings, this function has the same effect as in Excel.
This function is OpenFormula compatible.