stevedlawrence commented on a change in pull request #225: Implement
daf:lookAhead
URL: https://github.com/apache/incubator-daffodil/pull/225#discussion_r290264328
##########
File path:
daffodil-runtime1/src/main/scala/org/apache/daffodil/dpath/DAFFunctions.scala
##########
@@ -72,3 +78,63 @@ case object DAFError extends RecipeOp {
}
}
}
+
+case class DAFLookAhead(recipes: List[CompiledDPath])
+ extends FNTwoArgs(recipes) {
+
+ def computeValue(arg1: AnyRef, arg2: AnyRef, dstate: DState): AnyRef = {
+ val offset = arg1.asInstanceOf[JLong]
+ val lBitSize = arg2.asInstanceOf[JLong]
+
+ /*
+ * Since daf:lookAhead is defined to take unsigned arguements, the DPath
interperater
+ * will error out on the cast if a negative arguement is supplied, so we
do not need to SDE here.
+ */
+
+ Assert.invariant(offset >= 0)
+ Assert.invariant(lBitSize >= 0)
+
+ val totalLookahead = offset + lBitSize
+ if (totalLookahead > 512) {
Review comment:
This should be a constant variable, or maybe even a tunable? I don't see
anything code that actually has a limit of 512, so it seems this is just to
prevent people from accidentally doing the wrong thing or abusing this
function. A tunable probably make sense in that case, so if someone reeeeeally
wants to abuse this they can.
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