120 lines
3.2 KiB
Markdown
120 lines
3.2 KiB
Markdown
# EKP C Dynamic Module
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High-performance C implementation of the Knuth-Plass line breaking algorithm with multi-threaded parallel computation.
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## Architecture
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```
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ekp_c/
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├── ekp_module.h # Core data structures and API declarations
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├── ekp.c # Emacs module entry point (emacs_module_init)
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├── ekp_kp.c # Knuth-Plass DP algorithm + global state
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├── ekp_hyphen.c # Liang hyphenation with thread-safe caching
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├── ekp_paragraph.c # Text tokenization and box/glue construction
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├── ekp_thread_pool.c # Work-stealing thread pool
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└── Makefile # Build system
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```
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## Building
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```bash
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cd ekp_c
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make
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```
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Requirements:
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- C11 compiler (clang, gcc)
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- Emacs with dynamic module support (27.1+)
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- pthread library
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### Build Options
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```bash
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make DEBUG=1 # Debug build with sanitizers
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make clean # Remove build artifacts
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make info # Show build configuration
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make test # Run basic tests in Emacs
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```
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## Performance Optimizations
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### 1. Multi-threaded Processing
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- 8-thread pool for parallel DP candidate evaluation
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- Wavefront parallelization for large paragraphs (>100 boxes)
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- Lock-free work queue with condition variables
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### 2. O(1) Range Queries
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- Prefix sum arrays for ideal/min/max line widths
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- Eliminates repeated summation in inner DP loop
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### 3. Fast Hyphenation
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- FNV-1a hash for O(1) pattern lookup
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- Thread-safe LRU cache (4096 entries)
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- Read-write locks for concurrent access
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### 4. Memory Layout
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- Flat, cache-friendly data structures
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- Parallel arrays for boxes, glues, widths
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- Minimal allocations in hot paths
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## API
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### Initialization
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```elisp
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(ekp-c-init) ; Initialize module with thread pool
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(ekp-c-cleanup) ; Release all resources
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(ekp-c-version) ; => "1.0"
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(ekp-c-thread-count) ; => 8
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```
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### Hyphenation
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```elisp
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(ekp-c-load-hyphenator "/path/to/hyph_en_US.dic") ; => 0 (index)
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(ekp-c-hyphenate 0 "hyphenation") ; => (2 5 7)
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```
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### Line Breaking
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```elisp
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(ekp-c-break-lines
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"Your paragraph text here"
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0 ; hyphenator index
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600 ; line width in pixels
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#'string-pixel-width) ; measurement function
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;; Returns: ((breaks...) . total-cost)
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```
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### Parameters
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```elisp
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;; Spacing: (lws-i lws+ lws- mws-i mws+ mws- cws-i cws+ cws-)
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(ekp-c-set-spacing 7 3 2 5 2 1 0 2 0)
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;; Penalties: (line-penalty hyphen-penalty fitness-penalty last-line-ratio)
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(ekp-c-set-penalties 10 50 100 0.5)
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```
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## Design Notes
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Following Linus's philosophy:
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1. **Data structures are the code** - Get box/glue layout right, algorithm follows naturally
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2. **Simple thread model** - Fixed pool, no dynamic thread creation in hot path
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3. **Minimal abstraction** - Direct array access, no virtual dispatch
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4. **Fail fast** - Return NULL/nil on errors, let Emacs handle it
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## Benchmark
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Typical speedup vs pure Elisp implementation:
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| Paragraph Size | Elisp | C Module | Speedup |
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|----------------|-------|----------|---------|
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| 100 chars | 5ms | 0.3ms | 16x |
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| 500 chars | 45ms | 2ms | 22x |
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| 2000 chars | 350ms | 12ms | 29x |
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*Note: Actual performance depends on CPU, Emacs version, and text characteristics.*
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