- From: jean-frederic clere <jfrederic.clere@fujitsu-siemens.com>
- Date: Fri, 07 Nov 2003 12:12:26 +0100
- To: Markus Scherer <markus.scherer@jtcsv.com>
- Cc: ietf-charsets@iana.org, Guenther Kammermeier <guenther.kammermeier@fujitsu-siemens.com>, Martin Kraemer <Martin.Kraemer@fujitsu-siemens.com>
Markus Scherer wrote: > jean-frederic clere wrote: > >> For OSD_EBCDIC_DF04_1 and OSD_EBCDIC_DF04_15 that is a 8 bits >> roundtrip mapping but for 2 bytes mapping, undefined characters are >> mapped as '?' 0x6F. > > > Ok, so the substitution character for these tables is 0x6F. > > On the question of roundtrips, I think we are not communicating properly > due to a mismatch in terminology. > > I believe what you are saying is that these _tables_ as a whole perform > a roundtrip of their repertoire between a BS2000-EBCDIC codepage and the > Unicode portion corresponding to the equivalent ISO 8859 codepage. In > other words, the tables map between exactly N codes on the EBCDIC-based > and N Unicode code points. (N being the same on both sides, N=256 for > SBCS and N=128 for IRV.) Is this correct? Yes. > > Then, for every Unicode character _outside_ of this repertoire, there is > no mapping, and the default behavior is to use 0x6F as the substitution > character. Yes. > > What I was trying to ask was whether the individual _mappings_ in the > tables (each line in the text table listing) were roundtrip mappings. > This means that when you write something like > 0xFC 0x00DC #LATIN CAPITAL LETTER U WITH DIAERESIS > that means that you map Unicode U+00DC to 0xFC while converting from > Unicode to this charset, and you map 0xFC to Unicode U+00DC while > converting from the charset to Unicode. Fallback mappings only go one > way. Since many conversion implementations have fallback mappings in > addition to roundtrip mappings, they should be published, and should be > marked properly. See Unicode TR 22 for details. > > If the tables in your registration requests are pure remappings as > described above, then of course each mapping is a roundtrip mapping > > Is this how the converter implementation works on BS2000? Is it true > that BS2000 converters do not perform any fallback (one-way) mappings? Ok, the 3 mappings submitted are roundtrip mappings. > > Best regards, > markus > > Thanks for the comments Jean-Frederic
Received on Friday, 7 November 2003 06:14:19 UTC