I __think__ I understand what IBM is saying. You must differentiate between a "hex value" (0x00..0xFF) and a "code point" (a subset of "hex values"). Not every "hex value" is a "code point" in every CCSID. I.e. a single byte CCSID may have less than 256 "code points", or a double byte CCSID may have less than 65336 "code points". A "round trip" conversion from one CCSID to a different CCSID says that every possible "code point" in CCSID#1 will map to a unique "code point" in CCSID#1. I.e. the "trip" is on a two way street and you can "turn around" to go back to where you started. However, there may be a "one way" street from CCSID#2 to CCSID#1. So when you start in CCSID#2, you cannot just "turn around" when you get do CCSID#1 and return to your starting location.
Think of the "code points" in a CCSID as streets in a city. If the street is "two way" (round trip), then you can go back the way you came. If the street is "one way", then you can't. So CCSID#2 may have a "one way" street to CCSID#1. You can make the trip, but if you go back, you must use a different street. So when you go back to CCSID#2, you end up somewhere else in CCSID#2 from where you started. A "round trip" route from CCSID#1 to CCSID#2 means every street from CCSID#1 to CCSID#2 is "two way". But that does not mean that every street from CCSID#2 to CCSID#1 must be a "two way" street. There may be a "one way" trip from #2 to #1. So you cannot say that #2 is "round trip" to #1. That is, every "code point" in CCSID#2 must go to a "code point" in CCSID#1, but if more than one does, then the conversion is not classified "round trip". And it means that, so far as these conversions are concerned, if you use a hex value not in the set of "code points", nothing at all is guarnateed (you went "off road" so to speak). So "round trip" does not say that every "hex value" maps to a unique destination. In fact a "hex value" which is not a "code point" in a source CCSID could actually translate to a "hex value" which is a "code point" in the destination CCSID. I now have a headache and am going to have a lay down. -- John McKown Systems Engineer IV IT Administrative Services Group HealthMarkets(r) 9151 Boulevard 26 * N. Richland Hills * TX 76010 (817) 255-3225 phone * john.mck...@healthmarkets.com * www.HealthMarkets.com Confidentiality Notice: This e-mail message may contain confidential or proprietary information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. HealthMarkets(r) is the brand name for products underwritten and issued by the insurance subsidiaries of HealthMarkets, Inc. -The Chesapeake Life Insurance Company(r), Mid-West National Life Insurance Company of TennesseeSM and The MEGA Life and Health Insurance Company.SM > -----Original Message----- > From: IBM Mainframe Discussion List > [mailto:IBM-MAIN@bama.ua.edu] On Behalf Of Charles Mills > Sent: Wednesday, June 13, 2012 1:00 PM > To: IBM-MAIN@bama.ua.edu > Subject: Re: Anyone a Unicode Services expert? -- roundtrip conversion > > I got a response to the PMR. Taking the liberty of paraphrasing a long > reply, the essence of it seemed to be that -- per the CCSID > pair lists in > the manual -- they support round trip conversion from 1027 to > 1208 but not > from 1208 to 1027. Here is what I wrote back: > > It sounds like you are saying (for the CCSIDs in question) > "we support > round trip, but in one direction only." It would be like if I > bought a > round trip ticket on Delta between San Francisco and Atlanta, > and after > I got to Atlanta, they explained that it was a round trip > ticket only > in one direction. > > > > I would kind of question also whether what you are doing > conforms to > your definition of round trip in the Unicode manual glossary: > Round > trip. Encoding that occurs when every code point in the > source CCSID > maps to a unique code point in the target CCSID. Using round > trip > tables ensure the capability of reversing the conversion, and > > recovering the complete original source datastream. > > > > I would question "every code point in the source CCSID maps > to a unique > code point in the target CCSID" when both 3F and 41 map to > the same > code point, and I wonder how I would recover the original > source > datastream. > > Charles > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN > > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN
