[pdf-devel] [flyspray] Error management in type 4 functions

[GNU PDF Library]

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A new Flyspray task has been opened.  Details are below. 

User who did this - Jose E. Marchesi (jemarch) 

Attached to Project - GNU PDF Library
Summary - Error management in type 4 functions
Task Type - Planned Task
Category - FP Arithmetic Module
Status - NEXT
Assigned To - 
Operating System - All
Severity - Medium
Priority - Normal
Reported Version - START
Due in Version - BASE-LAYER-0
Due Date - Undecided
Details - From the ISO PDF reference, section 7.10.5.2, "Errors in Type 4 
Functions":

  "The part of a conforming reader that reads a type 4 function (analogous to 
the PostScript scanner) shall detect and report syntax errors. Any rerror detected 
by the conforming reader shall be errors in the PDF file and shall be handled like 
other errors in the file.

   The part of a conforming reader that executes a type 4 function (analogous 
to the PostScript interpreter) shall detect and report errors. This 
specification does not define a representation for the errors; those details 
shall be provided by the conforming reader that processes the PDF file. The 
following types of errors can occur (among others):
  
    - Stack overflow.
    - Stack underflow.
    - A type error (for example, applying 'not' to a real number).
    - A range error (for example, applying 'sqrt' to a negative number).
    - An undefined result (for example, dividing by 0)"

This task involves the following steps:

1) Determine a way for the 'pdf_fp_func_4_new' function to communicate syntax 
errors to the caller (an extra out parameter to the function seems to be a 
sensible way to achieve this).

2) Determine a list of syntax errors that will be managed and reported by 
'pdf_fp_func_4_new'.

3) Determine a way for the 'pdf_fp_func_eval' function to communicate type 4 
interpretation errors to the caller. Note that 'pdf_fp_func_eval' is used to 
evaluate type 0, type 2 and type 3 functions, so the solution should be quite 
generic (we may find useful to report errors in a detailed way from the 
evaluation of the other types of functions).

4) Determine a list of interpretation errors for type 4 functions that will be 
managed and reported by 'pdf_fp_func_eval'.

5) Implement the actual detection and reporting of errors.

6) Adapt the existing type 4 function unit tests to use the new API and write 
down negative unit tests to test the reporting of any defined syntax or 
interpretation error.

Please make sure to report to pdf-devel@ the results of 1), 2), 3) and 4) 
before to proceed with the actual implementation: we may want to brainstorm it.


More information can be found at the following URL:
http://www.gnupdf.org/flyspray/index.php?do=details&task_id=86

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