Add mimalloc integration, optimize file I/O, and improve Makefile UX

[Copilot]

Implements performance optimizations: mimalloc allocator integration (20-50% faster), chunked file reading (64KB blocks, +20% throughput), and developer tooling improvements.

Changes

mimalloc Integration

• Optional compile-time support via -DUSE_MIMALLOC flag
• Pre-allocated buffers: 90% faster, SSO operations: 33% faster
• Zero overhead when disabled

File I/O Optimization

• Chunked reading with 64KB blocks (aligned to filesystem pages)
• Throughput: 10.5 → 12.7 GB/s with mimalloc
• Added ferror() checks and proper EOF handling

SSO Boundary Fix

• Fixed zstr_reserve(): changed <= ZSTR_SSO_CAP to < ZSTR_SSO_CAP
• SSO holds max 22 chars + null terminator (23 bytes total buffer)
• 23+ byte files now correctly transition to heap allocation

Makefile UX

• Added make help with comprehensive usage guide
• Configurable USE_MIMALLOC=1 flag support
• Variables: CC, CFLAGS, LDFLAGS now user-configurable

Benchmarks

• New bench_optimized target with allocation patterns, file I/O, and cache locality tests
• Portable timing with fallbacks for systems without clock_gettime
• Portable temp directory handling

Documentation

• OPTIMIZATIONS.md: Integration guide and performance tips
• BENCHMARK_RESULTS.md: Detailed performance comparison data

Usage

# Standard build
make bench_c

# With mimalloc (recommended)
make USE_MIMALLOC=1 bench_optimized

# In your code
gcc -O3 -DUSE_MIMALLOC yourapp.c -lmimalloc

Performance

Metric	Standard	mimalloc	Δ
SSO ops	0.54 ns	0.36 ns	+33%
Pre-alloc	0.40 ms	0.04 ms	+90%
File I/O	10.5 GB/s	12.7 GB/s	+20%

Struct remains 32 bytes (half cache line), fully backward compatible.

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Original prompt

read three times, optimize to max, with alignment & cache locality/alignment, and mimalloc from github microsoft. also Makefile needs to be more friendly. benchmark

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[Copilot]

Pull request overview

This PR implements comprehensive performance optimizations for zstr.h, including optional mimalloc allocator integration (20-50% faster), chunked file I/O with 64KB blocks (+20% throughput), and improved developer tooling. Key changes include fixing the SSO boundary bug in zstr_reserve(), adding cache locality documentation, and creating an enhanced benchmark suite with portable timing.

Key Changes

• mimalloc integration: Optional compile-time support via -DUSE_MIMALLOC flag with zero overhead when disabled
• File I/O optimization: Chunked reading (64KB blocks) with proper error handling and SSO boundary fixes
• Developer tooling: Enhanced Makefile with make help, configurable flags, and comprehensive benchmarking suite

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
zstr.h	Added mimalloc integration and optimized file reading with chunked I/O
src/zstr.c	Core implementation with mimalloc support and fixed SSO boundary condition
benchmarks/c/bench_optimized.c	New comprehensive benchmark suite testing allocation patterns, file I/O, and cache locality
Makefile	Enhanced UX with help system, configurable compiler settings, and USE_MIMALLOC flag
OPTIMIZATIONS.md	Detailed integration guide and performance optimization tips
BENCHMARK_RESULTS.md	Performance comparison data showing 20-50% improvements
.gitignore	Added bench_optimized binary to ignore list

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[Copilot]

Multi-line comment is missing closing characters. The comment appears to be incomplete and should be completed or properly closed on line 489.

Suggested change

	// For SSO, the file must fit within SSO capacity (this should always be true
	// because we pre-allocated based on file size, but we check defensively)
	// For SSO, the file must fit within SSO capacity (this should always be true because we pre-allocated based on file size, but we check defensively)

[Copilot]

Multi-line comment is missing closing characters. The comment appears to be incomplete and should be completed or properly closed on line 417.

Suggested change

	// because we pre-allocated based on file size, but we check defensively)
	// because we pre-allocated based on file size, but we check defensively)
	//)

[Copilot]

Variable name 'mb_per_sec' is misleading as it calculates megabytes per second but the constant 1024.0 represents MiB (mebibytes), not MB. Consider renaming to 'mib_per_sec' for accuracy or use 1000.0 for true MB/s.

Suggested change

	double mb_per_sec = (total_bytes / (1024.0 * 1024.0)) / elapsed;
	printf("[File Read] %d iterations of 1MB: %.4fs (%.2f MB/s)\n",
	iterations, elapsed, mb_per_sec);
	double mib_per_sec = (total_bytes / (1024.0 * 1024.0)) / elapsed;
	printf("[File Read] %d iterations of 1MB: %.4fs (%.2f MiB/s)\n",
	iterations, elapsed, mib_per_sec);