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Zach NelsonandGitHub
c3f1dbfa09
## Summary **What is the goal of this PR?** This change avoids the pattern of creating a `std::string` using `.substr` in order to compare against a file extension literal. ```c++ std::string path; if (path.length() >= 4 && path.substr(path.length() - 4) == ".ext") ``` The `checkFileExtension` utility has moved from StringUtils to FsHelpers, to be available to code in lib/. The signature now accepts a `std::string_view` instead of `std::string`, which makes the single implementation reusable for Arduino `String`. Added utility functions for commonly repeated extensions. These changes **save about 2 KB of flash (5,999,427 to 5,997,343)**. --- ### AI Usage While CrossPoint doesn't have restrictions on AI tools in contributing, please be transparent about their usage as it helps set the right context for reviewers. Did you use AI tools to help write this code? _**NO**_
# XTC/XTCH Library XTC ebook format support for CrossPoint Reader. ## Supported Formats | Format | Extension | Description | |--------|-----------|----------------------------------------------| | XTC | `.xtc` | Container with XTG pages (1-bit monochrome) | | XTCH | `.xtch` | Container with XTH pages (2-bit grayscale) | ## Format Overview XTC/XTCH are container formats designed for ESP32 e-paper displays. They store pre-rendered bitmap pages optimized for the XTeink X4 e-reader (480x800 resolution). ### Container Structure (XTC/XTCH) - 56-byte header with metadata offsets - Optional metadata (title, author, etc.) - Page index table (16 bytes per page) - Page data (XTG or XTH format) ### Page Formats #### XTG (1-bit monochrome) - Row-major storage, 8 pixels per byte - MSB first (bit 7 = leftmost pixel) - 0 = Black, 1 = White #### XTH (2-bit grayscale) - Two bit planes stored sequentially - Column-major order (right to left) - 8 vertical pixels per byte - Grayscale: 0=White, 1=Dark Grey, 2=Light Grey, 3=Black ## Reference Original format info: <https://gist.github.com/CrazyCoder/b125f26d6987c0620058249f59f1327d>