#1: UPT Assembler instruction Author: asr2, Location: GermanyPosted: Tue May 08, 2012 3:13 am — The Update Tree instruction is probably the least understood z/Architecture instruction, not helped by the confusing description in the PoPs, in particular in the case of processing to be performed for equal codewords.
To empirically investigate the behaviour, I wrote a very simple program with a tree containing 2 and 3, elements respectively; each tree element has the same codeword. In both cases, UPT returns 8 as index - why? According to the instruction flowchart in the PoPs, the tree should be processed from the leaf towards the root: why then is 16 (decimal) not returned as index in the 3-element case?
When the codewords are unequal, UPT executes as expected.
