Am 19.10.2025 um 04:57 schrieb Aaron M. Ucko: Hello,
I have found that when a PNG image's row width does not correspond to a whole number of bytes, the low-order bits of the last byte in each uncompressed row can fluctuate between pdflatex runs, at least when libpng can perform SIMD-assisted decompression, yielding nondeterministic output even when arranging to supply predetermined timestamps. (Moreover, this fluctuation can affect the length of the resulting compressed stream, slightly shifting the file position of subsequent content.)
At least I'm able to reproduce the issue by running pdflatex 10 times over the same set of input files and getting 10 files having the same size but different checksum.
The input files are of course not minimal. As next step I'll contact pdfTeX upstream. They should be able to clarify if the code generating that alternating content is located on the pdfTeX source code or in one of the libraries it is linked with.
Hilmarhille@rasppi3:~/devel/TeXLive/Upgrade_Test/arm64-sid/home/hille/1118385 $ ls -l
total 109240 drwxr-xr-x 2 hille hille 36864 May 11 08:55 latex -rw-rw-r-- 1 hille hille 11178538 May 11 08:55 refman_10.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:18 refman_1.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:22 refman_2.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:26 refman_3.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:31 refman_4.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:35 refman_5.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:39 refman_6.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:43 refman_7.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:47 refman_8.pdf -rw-rw-r-- 1 hille hille 11178538 May 11 08:51 refman_9.pdfhille@rasppi3:~/devel/TeXLive/Upgrade_Test/arm64-sid/home/hille/1118385 $ md5sum refman_*
fad47cf92f41fcee69bcaba215fc54fb refman_10.pdf 70e2b4061750d4f70089a1571d59bef1 refman_1.pdf 5b897de682ef50f5ac423b60fdedd9b7 refman_2.pdf c4862f7dd9aba1a41c66577e6cc4908f refman_3.pdf 2b987c9a15fafe4d83e0e0745d2cd197 refman_4.pdf a8a28203556c3fd7b261d8a3532b198e refman_5.pdf 0dc8adff9c21b34633786cf993edd2f3 refman_6.pdf e3c4783783b132c8b6888d12144d6a58 refman_7.pdf 9c5bc607de841902487556fb4c080746 refman_8.pdf a50e84bb0d679d778bd6d21980714ebd refman_9.pdf -- sigfault
OpenPGP_signature.asc
Description: OpenPGP digital signature
