Fix SegmentReader bugs #134
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added 2 commits
August 31, 2023 20:12
Prior to this change, the start index was treated as a byte index rather than a word index.
Both Structs and Lists support two's complement "Signed" offsets: > B (30 bits) = Offset, in words, from the end > of the pointer to the start of the struct's > data section. Signed. > B (30 bits) = Offset, in words, from the end > of the pointer to the start of the first > element of the list. Signed. The prior code only supported positive offsets because it used the Java >>> operator, which is an unsigned shift operator. The Java >> operator is the signed shift operator. Audited the remaining uses of the shift operator; they were correct and they are documented as such. Positive offsets are only guaranteed in a Canonical message.
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Wow! Good catch! |
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There are two bugs, one for each of the two first commits:
1 - Support signed offsets for Structs and Lists pointers
Both Structs and Lists support two's complement "Signed" offsets:
The prior code only supported positive offsets because it used the Java
>>>operator, which is an unsigned shift operator. The Java>>operator is the signed shift operator.Audited the remaining uses of the shift operator; they were correct and they are documented as such.
Positive offsets are only guaranteed in a Canonical message.
2 - Word arithmetic should be used for bounds checking
Prior to this change, the start index was treated as a byte index rather than a word index.