fastnum 0.2.10

Fast decimal numbers library
Documentation 
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use std::{
    env,
    path::{Path, PathBuf},
};

const DEFAULT_ROUNDING_MODE: &str = "HalfUp";
const FMT_EXPONENTIAL_LOWER_THRESHOLD: &str = "5";
const FMT_EXPONENTIAL_UPPER_THRESHOLD: &str = "15";
const FMT_MAX_INTEGER_PADDING: &str = "1000";
const SERDE_DESERIALIZE_MODE: &str = "Strict";

fn main() {
    let out_dir: PathBuf = env::var_os("OUT_DIR").unwrap().into();
    write_default_rounding_mode(&out_dir);
    write_exponential_format_threshold(&out_dir);
    write_serde_deserialize_mode(&out_dir);
}

macro_rules! load_env {
    ($env:ident, $name:literal, $default:ident) => {{
        println!("cargo:rerun-if-env-changed={}", $name);
        $env::var($name).unwrap_or_else(|_| $default.to_owned())
    }};
}

fn write_default_rounding_mode(out_dir: &Path) {
    let rounding_mode_name = load_env!(
        env,
        "RUST_FASTNUM_DEFAULT_ROUNDING_MODE",
        DEFAULT_ROUNDING_MODE
    );

    let rust_file_path = out_dir.join("default_rounding_mode.rs");
    let rust_file_contents = format!(
        "const DEFAULT_ROUNDING_MODE: RoundingMode = RoundingMode::{};",
        rounding_mode_name
    );

    std::fs::write(rust_file_path, rust_file_contents).unwrap();
}

fn write_exponential_format_threshold(out_dir: &Path) {
    let low_value = load_env!(
        env,
        "RUST_FASTNUM_FMT_EXPONENTIAL_LOWER_THRESHOLD",
        FMT_EXPONENTIAL_LOWER_THRESHOLD
    );
    let high_value = load_env!(
        env,
        "RUST_FASTNUM_FMT_EXPONENTIAL_UPPER_THRESHOLD",
        FMT_EXPONENTIAL_UPPER_THRESHOLD
    );
    let max_padding = load_env!(
        env,
        "RUST_FASTNUM_FMT_MAX_INTEGER_PADDING",
        FMT_MAX_INTEGER_PADDING
    );

    let low_value: u32 = low_value
        .parse::<std::num::NonZeroU32>()
        .expect("$RUST_FASTNUM_FMT_EXPONENTIAL_LOWER_THRESHOLD must be an integer > 0")
        .into();

    let high_value: u32 = high_value
        .parse::<u32>()
        .expect("$RUST_FASTNUM_FMT_EXPONENTIAL_UPPER_THRESHOLD must be valid u32");

    let max_padding: u32 = max_padding
        .parse::<u32>()
        .expect("$RUST_FASTNUM_FMT_MAX_INTEGER_PADDING must be valid u32");

    let rust_file_path = out_dir.join("exponential_format_threshold.rs");

    let rust_file_contents = [
        format!(
            "const EXPONENTIAL_FORMAT_LEADING_ZERO_THRESHOLD: usize = {};",
            low_value
        ),
        format!(
            "const EXPONENTIAL_FORMAT_TRAILING_ZERO_THRESHOLD: usize = {};",
            high_value
        ),
        format!("const FMT_MAX_INTEGER_PADDING: usize = {};", max_padding),
    ];

    std::fs::write(rust_file_path, rust_file_contents.join("\n")).unwrap();
}

fn write_serde_deserialize_mode(out_dir: &Path) {
    let mode = load_env!(
        env,
        "RUST_FASTNUM_SERDE_DESERIALIZE_MODE",
        SERDE_DESERIALIZE_MODE
    );

    let rust_file_path = out_dir.join("serde_deserialize_mode.rs");
    let rust_file_contents = format!(
        "const SERDE_DESERIALIZE_MODE: DeserializeMode = DeserializeMode::{};",
        mode
    );

    std::fs::write(rust_file_path, rust_file_contents).unwrap();
}