|
1 |
Defect Report Number: 8632-2/002
|
|
2 |
Submitter: Henderson
|
|
3 |
Addressed to: JTC1/SC 24/WG 6 Rapporteur Group on ISO/IEC 8632, CGM
|
|
4 |
WG secretariat: NNI
|
|
5 |
Date Circulated by WG secretariat: 1 July 1995
|
|
6 |
Deadline on response from editor: : 1 October 1995
|
|
7 |
Defect Report concerning IS 8632:1992 Computer Graphics: Metafile for the storage and transfer of picture description information (CGM) Part 2, Character encoding.
|
|
8 |
Qualifier (e.g. error, omission, clarification required): Clarification
|
|
9 |
References in document (e.g. page, clause, figure and/or table numbers):page 30, clause 6.15
|
|
10 |
Nature of defect (complete, concise explanation of the perceived problem):
All data bytes of operands of the BS data type will have bit 7 set (1). ESC, which is the first character of SOS and ST in the 7-bit environment, has bit 7 clear (0) (SOS and ST in the 8-bit environment also have bit 7 clear). Therefore normally an interpreter can look for a character from column 0 (ESC) to signal the end of the data. This, however, will not work if ESC is substituted in which case ST becomes 7/14 5/11 5/12 — all three codes are indistinguishable from valid data bytes.
|
|
11 |
Solution proposed by the submitter (optional):
Do not change the syntax of BS parameters, but document the problem and a work-around for implementations. Add to clause 6.15: "Note — All data bytes of operands of the BS data type will have bit 7 set (1). ESC, which is the first character of SOS and ST in the 7-bit environment, has bit 7 clear (0) (SOS and ST in the 8-bit environment also have bit 7 clear). Therefore normally an interpreter can look for a character from column 0 (ESC) to signal the end of the data. This, however, will not work if ESC is substituted in which case ST becomes 7/14 5/11 5/12 — all three codes are indistinguishable from valid data bytes. The BS parameter occurs only in Tile and Bitonal Tile elements. In both cases it is the last parameter. If ESC is substituted, the interpreters can look for the 3-code sequence 7/14 5/11 5/12, which will be the equivalent of ST in the 7-bit environment, and look for an opcode byte next. This should reliably terminate the BS parameter. Registration proposals which use the BS data type should be aware of this and design the data parameterization so that indeterminancies are avoided. Explicit solutions could be required in some cases, for example the case of two consecutive BS parameters. An example of such an explicit solution is a length parameter to define the size of the BS parameter (which would still necessarily have the standard-mandated SOS/ST terminators)."
|
|
12 |
Editor's response (any material proposed for processing as a technical corrigendum to, an amendment to, or a commentary on the International Standard or DIS final text is attached separately to this completed report):Amend the standard as proposed above.
|