Eyevinn / hi264 / 37926699395

88%

main: 88%

Build Type

Pull #34

github

Committed by tobbee

Commit Message

fix: bound the coeff_abs_level_minus1 Exp-Golomb prefix

The Exp-Golomb suffix of coeff_abs_level_minus1 counted bypass bins until a 0 with no limit, the last CABAC syntax element loop without one after the bound on mb_qp_delta. It cannot spin forever, since bypass bins turn to 0 within a few steps once the data runs out, but a corrupt slice could keep it going for as long as it has bits.

Clause 8.5 keeps the scaled coefficients within -2^(7 + bitDepth)..2^(7 + bitDepth) - 1. Even the smallest scaling, an 8x8 block at qP 0 with a scaling list weight of 1 (18/64 per level), then keeps a level below 2^(9 + bitDepth), so a conforming prefix has at most 8 + bitDepth bins, 16 for 8-bit video. A longer prefix returns an error, which DecodeResidual and decodeResidualMB now pass up to the macroblock loop.

The bit-depth-dependent limits now live in internal/slice/limits.go as named constants and helpers, including the mb_qp_delta bound from the previous fix and the QPY wrap of equation 7-37 in both entropy coders, so they follow the bit depth if more than 8 bits are supported.

Pull Request Pull Request #34: fix: report a CABAC slice that needs bits past the end of its data

Coverage Stats

56 of 74 new or added lines in 6 files covered. (75.68%)

5 existing lines in 1 file now uncovered.

8529 of 9682 relevant lines covered (88.09%)

1.02 hits per line