structured-zstd 0.0.50

//! C-side counterpart of `encode_loop_z000033`, for instruction-count and
//! cycle comparisons under `perf stat`.
//!
//! Same shape as the Rust loop: read the corpus once, allocate the output
//! buffer once, then compress it N times at the given level through the
//! upstream `ZSTD_compress` one-shot API. Keeping the two binaries
//! structurally identical is the point — the difference in retired
//! instructions is then attributable to the encoders, not to harness
//! overhead.
//!
//! Build: `cargo build --release -p ffi-bench --example ffi_encode_loop_z000033`
//! Run:   `perf stat -e cycles,instructions ./ffi_encode_loop_z000033 <level> <iters> <corpus>`

use std::env;
use std::fs;

use zstd::zstd_safe::zstd_sys;

fn main() {
    let level: i32 = env::args().nth(1).and_then(|s| s.parse().ok()).unwrap_or(3);
    let iters: usize = env::args()
        .nth(2)
        .and_then(|s| s.parse().ok())
        .unwrap_or(40);
    let corpus_path = env::args()
        .nth(3)
        .unwrap_or_else(|| "zstd/decodecorpus_files/z000033".to_string());

    let bytes = fs::read(&corpus_path).expect("read corpus");
    let bound = unsafe { zstd_sys::ZSTD_compressBound(bytes.len()) };
    let mut out = vec![0u8; bound];

    // Summed so the optimiser cannot drop the calls, mirroring the Rust loop.
    let mut sum = 0usize;
    for _ in 0..iters {
        let written = unsafe {
            zstd_sys::ZSTD_compress(
                out.as_mut_ptr().cast(),
                out.len(),
                bytes.as_ptr().cast(),
                bytes.len(),
                level,
            )
        };
        assert!(
            unsafe { zstd_sys::ZSTD_isError(written) } == 0,
            "ZSTD_compress failed"
        );
        sum += written;
    }

    println!(
        "encoded {} bytes x {} iters at level {}; last-out-sum={}",
        bytes.len(),
        iters,
        level,
        sum
    );
}