Artifact 1027cba83cc7a791a19ac90a2d30721e1d3b3b0a1c158242683d33795ef64f2d:
Extend the full-form (.zlib) compression-headroom probe with a dictionary sub-arm: train a candidate preset dictionary on the sampled full-form population and recompress the SAME frames with it preloaded, reporting the net byte gain over the empty-window baseline. This is the GO/NO-GO signal for adding a preset-dictionary frame class. At-rest MEASUREMENT only: it never touches the store or the production §4.1 codec, and it preloads the dictionary through a throwaway reference-difference method because Zig 0.16 std flate hardcodes FDICT=0 and exposes no setDictionary.
The dictionary-compression lineage this arm measures: RFC 1950 reserves the FDICT bit and the 32 KiB preset-dictionary window, and its §9 says the most- referenced strings belong at the dictionary tail (shortest back-references); Yann Collet's zstd --train/COVER is the reference for training a shared dictionary from a population of small, mutually-similar records; Chromium productionised shared-dictionary transport at scale (SDCH, later the Compression-Dictionary-Transport work); Fabrice Bellard's LZEXE established the practical art of squeezing highly-repetitive input with a tiny back- reference machine. by dmestas on 2026-07-18 17:47:47.
C storage-bench:\sadd\sa\sdict-trained\sheadroom\sarm\s(§2.2\spreset-dictionary\sGO/NO-GO)\n\nExtend\sthe\sfull-form\s(.zlib)\scompression-headroom\sprobe\swith\sa\sdictionary\nsub-arm:\strain\sa\scandidate\spreset\sdictionary\son\sthe\ssampled\sfull-form\npopulation\sand\srecompress\sthe\sSAME\sframes\swith\sit\spreloaded,\sreporting\sthe\nnet\sbyte\sgain\sover\sthe\sempty-window\sbaseline.\sThis\sis\sthe\sGO/NO-GO\ssignal\nfor\sadding\sa\spreset-dictionary\sframe\sclass.\sAt-rest\sMEASUREMENT\sonly:\sit\nnever\stouches\sthe\sstore\sor\sthe\sproduction\s§4.1\scodec,\sand\sit\spreloads\sthe\ndictionary\sthrough\sa\sthrowaway\sreference-difference\smethod\sbecause\sZig\s0.16\nstd\sflate\shardcodes\sFDICT=0\sand\sexposes\sno\ssetDictionary.\n\nThe\sdictionary-compression\slineage\sthis\sarm\smeasures:\sRFC\s1950\sreserves\sthe\nFDICT\sbit\sand\sthe\s32\sKiB\spreset-dictionary\swindow,\sand\sits\s§9\ssays\sthe\smost-\nreferenced\sstrings\sbelong\sat\sthe\sdictionary\stail\s(shortest\sback-references);\nYann\sCollet's\szstd\s--train/COVER\sis\sthe\sreference\sfor\straining\sa\sshared\ndictionary\sfrom\sa\spopulation\sof\ssmall,\smutually-similar\srecords;\sChromium\nproductionised\sshared-dictionary\stransport\sat\sscale\s(SDCH,\slater\sthe\nCompression-Dictionary-Transport\swork);\sFabrice\sBellard's\sLZEXE\sestablished\nthe\spractical\sart\sof\ssqueezing\shighly-repetitive\sinput\swith\sa\stiny\sback-\nreference\smachine. 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