build.rs

use std::env;
use std::fs::File;
use std::io::Write;
use std::path::Path;

const BIT_REVERSE_TABLE: [u16; 256] = [
    0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0, 
    0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8, 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8, 
    0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4, 
    0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC, 
    0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2, 0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2, 
    0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA, 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
    0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6, 
    0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE, 0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
    0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
    0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9, 
    0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5, 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
    0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
    0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3, 
    0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB, 0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
    0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7, 
    0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF];

fn write_table(name: &str, aliases: &[&str], mut poly: u16, refin: bool, f: &mut File) {
    f.write_all(format!("const {}_TABLE: [u16; 256] = [", name).as_bytes()).unwrap();

    if refin {
        poly = (BIT_REVERSE_TABLE[(poly & 0xFF) as usize]) << 8
             | (BIT_REVERSE_TABLE[(poly >> 8) as usize]);
    }

    for mut x in 0u16..256 {
        if ! refin {
            x = x << 8;
        }
        for _ in 0..8 {
            if refin {
                x = if x & 1 > 0 { (x >> 1) ^ poly } else { x >> 1 };
            } else {
                x = if x & 0x8000 > 0 { (x << 1) ^ poly } else { x << 1 };
            }
        }
        f.write_all(format!("0x{:04x}, ", x).as_bytes()).unwrap();
    }

    f.write_all(b"];\n").unwrap();

    for alias in aliases {
        let line = format!("const {}_TABLE: &'static [u16] = &{}_TABLE;\n", alias, name);
        f.write_all(line.as_bytes()).unwrap();
    }
}

fn main() {
    let out_dir = env::var("OUT_DIR").unwrap();
    let dest_path = Path::new(&out_dir).join("tables.rs");
    let mut f = File::create(&dest_path).unwrap();

    write_table("ARC", &["MAXIM", "USB", "MODBUS"], 0x8005, true, &mut f);
    write_table("AUG_CCITT", &["CCITT_FALSE", "GENIBUS", "XMODEM"], 0x1021, false, &mut f);
    write_table("BUYPASS", &["DDS_110"], 0x8005, false, &mut f);
    write_table("CDMA2000", &[], 0xC867, false, &mut f);
    write_table("DECT_R", &["DECT_X"], 0x0589, false, &mut f);
    write_table("DNP", &[], 0x3D65, true, &mut f);
    write_table("EN_13757", &[], 0x3D65, false, &mut f);
    write_table("MCRF4XX", &["RIELLO", "TMS37157", "CRC_A", "KERMIT", "X_25"], 0x1021, true, &mut f);
    write_table("T10_DIF", &[], 0x8BB7, false, &mut f);
    write_table("TELEDISK", &[], 0xA097, false, &mut f);
}