Hi,
I have a problem in understanding Aligned PER decoding of string. This is mainly regarding Padding bits.
This is an excerpt from ASN.1 complete by John Larmouth,
Padding bits
"When do we get padding bits in the ALIGNED case?
Here we need to look at the combination of the effective
size constraint (which restricts the number of abstract
characters in every value) and the effective alphabet
constraint (which determines the number of bits used to
encode each character).
If the combination of these is such that the total encoding size for a value of this constrained type can never exceed sixteen bits, then there are no padding bits. The character string value is encoded into a bit-field. If, however, there are some values which might require more than 16 bits, then the encoding is into an octetaligned bit-field, and no character will cross an octet boundary (in the ALIGNED case)."
I did not understand the terminology used here.
What is effective size constraint mentioned here?
-- Is it the number of characters in that string or the upper bound value the string can take.
For Ex: myString OCTETSTRING(FROM 1...128)
Is effective string constraint equal to 128(Upper bound) or equal to the no of characters in the string obtained by finding the length determinant.
What does this mean ? "Which restricts the number of abstract characters in every value."
Is Total Encoding size equal to
a) The number of characters in the string multiplied by the number of bits required for encoding each character
or
b) The number of characters in the string multiplied by the number of bits required for encoding each character + Bits used for Length Determinant?
or
c) Upper bound value the string can take multiplied by the number of bits required for encoding each character.
Please explain me with an example of encoding strings in the ALIGNED case, where padding bits are required and not required.
Regards
Surya Santosh
Exclusive NRI offer! Get a Zero Balance Account for next 20 years
_______________________________________________ ASN1 mailing list [email protected] http://lists.asn1.org/mailman/listinfo/asn1
