id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
1481	computation overflow in HM reference C model	swong10	swong10	"We may have found a bug in the HM model.  There is a mismatch between the written specification and HM reference C model. 

Dec 2016 Spec: 8.4.4.2.7 Decoding process for palette mode

HM code version : HM-16.15+SCM-8.5
Function :  TDecCu::xDecodePaletteTexture() in TDecCu.cpp
The problem equation happens in both clauses of an if-else statement.
The overflow happens in tmpVal, which is used to store the inverse quantized palette escape values in (8-77).
tmpVal is then clipped according to (8-78) to generate the reconstructed samples. 
levelScale <= 72 (7-bit).
 
In SCM, tmpVal is of type “Pel”. So, once we changed Pixel from Short to Int the overflow was fixed. 

It is a high bit depth problem, most likely only happen when pixel depth is > 8-bit.


"	defect	closed	major		HM SCC		fixed	overflow, palette	jct-vc@…