Commit a46c111d9f3642f0ef3819e7298846ccc61869e0
2020-07-27T14:21:23
Further jpeg_skip_scanlines() fixes - Introduce a partial image decompression regression test script that validates the correctness of jpeg_skip_scanlines() and jpeg_crop_scanlines() for a variety of cropping regions and libjpeg settings. This regression test catches the following issues: #182, fixed in 5bc43c7821df982f65aa1c738f67fbf7cba8bd69 #237, fixed in 6e95c08649794f5018608f37250026a45ead2db8 #244, fixed in 398c1e9acc9b4531edceb3d77da0de5744675052 #441, fully fixed in this commit It does not catch the following issues: #194, fixed in 773040f9d949d5f313caf7507abaf4bd5d7ffa12 #244 (additional segfault), fixed in 9120a247436e84c0b4eea828cb11e8f665fcde30 - Modify the libjpeg-turbo regression test suite (make test) so that it checks for the issue reported in #441 (segfault in jpeg_skip_scanlines() when used with 4:2:0 merged upsampling/color conversion.) - Fix issues in jpeg_skip_scanlines() that caused incorrect output with h2v2 (4:2:0) merged upsampling/color conversion. The previous commit fixed the segfault reported in #441, but that was a symptom of a larger problem. Because merged 4:2:0 upsampling uses a "spare row" buffer, it is necessary to allow the upsampler to run when skipping rows (fancy 4:2:0 upsampling, which uses context rows, also requires this.) Otherwise, if skipping starts at an odd-numbered row, the output image will be incorrect. - Throw an error if jpeg_skip_scanlines() is called with two-pass color quantization enabled. With two-pass color quantization, the first pass occurs within jpeg_start_decompress(), so subsequent calls to jpeg_skip_scanlines() interfere with the multipass state and prevent the second pass from occurring during subsequent calls to jpeg_read_scanlines().