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subhobhai943andClaude Opus 4.8
db962de248
Adds a from-scratch baseline JPEG decoder (ITU-T T.81, SOF0 sequential DCT), so the Web app now displays the web's dominant photo format alongside PNG and BMP. image_decode dispatches on the JPEG magic, so the browser needs no change beyond that. lib/jpeg.c handles grayscale and YCbCr, arbitrary chroma subsampling (4:4:4/4:2:2/4:2:0), restart markers, and multiple DQT/DHT tables. Huffman uses canonical tables (counts + symbols, like the inflate decoder) to avoid a large fast-table; the transform is the standard fixed-point integer row/column IDCT; colour is integer YCbCr->RGB. All heap-allocated, no floating point, so it is safe in the freestanding kernel. Progressive (SOF2) and arithmetic-coded JPEGs are rejected rather than mis-decoded. Verified on the host against PIL-encoded references before going in the kernel, the same way the crypto and PNG decoders were: grayscale decodes at mean absolute error 0.9/channel, 4:4:4 at 1.7 (pure IDCT rounding vs libjpeg), and 4:2:0 at 4.3 (nearest-neighbour chroma upsampling softens colour edges -- a known, visually-fine artifact). In QEMU the Web app fetched a 400x260 JPEG over HTTP and rendered it correctly -- gradient, an antialiased red circle, a green box, a yellow diagonal. Builds clean on x86_64, aarch64 and armv8i. Limits: baseline only (no progressive), and chroma upsampling is nearest-neighbour rather than the smoother interpolation libjpeg uses. The browser still shows images by URL, not inline in a page. Co-Authored-By: Claude Opus 4.8 <[email protected]> Claude-Session: https://claude.ai/code/session_01Fh5z6V7nGPbHvqVG5p4CXX