rust-secp256k1-unsafe-fast/secp256k1-sys/build.rs

// SPDX-License-Identifier: CC0-1.0

//! # Build script

// Coding conventions
#![deny(non_upper_case_globals)]
#![deny(non_camel_case_types)]
#![deny(non_snake_case)]
#![deny(unused_mut)]
#![warn(missing_docs)]

extern crate cc;

use std::env;

fn main() {
    // Actual build
    let mut base_config = cc::Build::new();
    base_config.include("depend/secp256k1/")
               .include("depend/secp256k1/include")
               .include("depend/secp256k1/src")
               .flag_if_supported("-Wno-unused-function") // some ecmult stuff is defined but not used upstream
               .flag_if_supported("-Wno-unused-parameter") // patching out printf causes this warning
               .define("SECP256K1_API", Some(""))
               .define("ENABLE_MODULE_ECDH", Some("1"))
               .define("ENABLE_MODULE_SCHNORRSIG", Some("1"))
               .define("ENABLE_MODULE_EXTRAKEYS", Some("1"))
               .define("ENABLE_MODULE_ELLSWIFT", Some("1"))
               // upstream sometimes introduces calls to printf, which we cannot compile
               // with WASM due to its lack of libc. printf is never necessary and we can
               // just #define it away.
               .define("printf(...)", Some(""));

    if cfg!(feature = "lowmemory") {
        base_config.define("ECMULT_WINDOW_SIZE", Some("4")); // A low-enough value to consume negligible memory
        base_config.define("ECMULT_GEN_PREC_BITS", Some("2"));
    } else {
        // definitely slower, not meaningful
        // base_config.define("ECMULT_GEN_PREC_BITS", Some("2"));

        // base_config.define("ECMULT_GEN_PREC_BITS", Some("4"));

        // going from the default 4 to 8 is a huge performance increase
        // when combined with other optimizations
        base_config.define("ECMULT_GEN_PREC_BITS", Some("8"));

        // TODO highly experimental
        // non-standard optimization
        // slow compilation
        // base_config.define("ECMULT_GEN_PREC_BITS", Some("16"));

        // minor factor, the 15 default is already optimized
        base_config.define("ECMULT_WINDOW_SIZE", Some("15")); // This is the default in the configure file (`auto`)

        // TODO do some fine tuning for a slightly higher than default ECMULT_WINDOW_SIZE
        // base_config.define("ECMULT_WINDOW_SIZE", Some("17"));
        // base_config.define("ECMULT_WINDOW_SIZE", Some("18"));

        // too large
        // base_config.define("ECMULT_WINDOW_SIZE", Some("22"));
    }
    base_config.define("USE_EXTERNAL_DEFAULT_CALLBACKS", Some("1"));
    #[cfg(feature = "recovery")]
    base_config.define("ENABLE_MODULE_RECOVERY", Some("1"));

    // WASM headers and size/align defines.
    if env::var("CARGO_CFG_TARGET_ARCH").unwrap() == "wasm32" {
        base_config.include("wasm/wasm-sysroot")
                   .file("wasm/wasm.c");
    }

    // secp256k1
    base_config.file("depend/secp256k1/contrib/lax_der_parsing.c")
               .file("depend/secp256k1/src/precomputed_ecmult_gen.c")
               .file("depend/secp256k1/src/precomputed_ecmult.c")
               .file("depend/secp256k1/src/secp256k1.c");


    // default CC is gcc on the tested system
    // GCC 12.2 slightly faster than clang-18 for the unmodified code?

    // for the modified code, clang is slightly faster?

    // // force clang
    base_config.compiler("clang");

    // // gcc is faster without native CPU settings on a Ryzen Zen 3 desktop CPU
    base_config.flag("-march=native");

    // doesn't work as-is
    // base_config.flag("-flto=thin");

    // shouldn't do much
    base_config.define("NDEBUG", Some(""));

    // enable custom modifications on the codebase
    base_config.define("OPTIMIZE_UNSAFE_VAR_VARIANT", Some(""));
    base_config.define("OPTIMIZE_UNSAFE_SHORTCIRCUIT", Some(""));
    base_config.define("OPTIMIZE_UNSAFE_SKIP_ZEROING", Some(""));
    base_config.define("OPTIMIZE_UNSAFE_ECMULT_GEN_CORE", Some(""));
    base_config.define("OPTIMIZE_UNSAFE_SKIP_MASKING", Some(""));

    // This is slower, and removed in a future secp256k1 code version
    // base_config.define("USE_ASM_X86_64", Some(""));

    // -O3 seems to be better than -O2 for clang
    // -O3 is already the default for --release builds
    // set anyway so that rust non-release builds don't fall back to -O1 here
    base_config.flag("-O3");

    // base_config.flag("-O1");
    // Extra slow, for benchmark testing
    // base_config.flag("-Os");

    // the default seems to set -gdwarf-4
    // slightly worse on gcc?
    // slightly better on clang-18 ?
    // base_config.flag("-g0");

    // potential minor improvement
    // to counteract the -fno-omit-frame-pointer
    // base_config.flag("-fomit-frame-pointer");


    if base_config.try_compile("libsecp256k1.a").is_err() {
        // Some embedded platforms may not have, eg, string.h available, so if the build fails
        // simply try again with the wasm sysroot (but without the wasm type sizes) in the hopes
        // that it works.
        // base_config.include("wasm/wasm-sysroot");
        // base_config.compile("libsecp256k1.a");
    }

}