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use std::env;
use std::fs::File;
use std::io::{self, Write};
use std::path::{Path, PathBuf};
const CASTAGNOLI_POLY: u32 = 0x82f63b78;
type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
fn main() {
if let Err(err) = try_main() {
panic!("{}", err);
}
}
fn try_main() -> Result<()> {
let out_dir = match env::var_os("OUT_DIR") {
None => {
return Err(From::from("OUT_DIR environment variable not defined"))
}
Some(out_dir) => PathBuf::from(out_dir),
};
write_tag_lookup_table(&out_dir)?;
write_crc_tables(&out_dir)?;
Ok(())
}
fn write_tag_lookup_table(out_dir: &Path) -> Result<()> {
let out_path = out_dir.join("tag.rs");
let mut out = io::BufWriter::new(File::create(out_path)?);
writeln!(out, "pub const TAG_LOOKUP_TABLE: [u16; 256] = [")?;
for b in 0u8..=255 {
writeln!(out, " {},", tag_entry(b))?;
}
writeln!(out, "];")?;
Ok(())
}
fn tag_entry(b: u8) -> u16 {
let b = b as u16;
match b & 0b00000011 {
0b00 => {
let lit_len = (b >> 2) + 1;
if lit_len <= 60 {
lit_len
} else {
assert!(lit_len <= 64);
(lit_len - 60) << 11
}
}
0b01 => {
let len = 4 + ((b >> 2) & 0b111);
let offset = (b >> 5) & 0b111;
(1 << 11) | (offset << 8) | len
}
0b10 => {
let len = 1 + (b >> 2);
(2 << 11) | len
}
0b11 => {
let len = 1 + (b >> 2);
(4 << 11) | len
}
_ => unreachable!(),
}
}
fn write_crc_tables(out_dir: &Path) -> Result<()> {
let out_path = out_dir.join("crc32_table.rs");
let mut out = io::BufWriter::new(File::create(out_path)?);
let table = make_table(CASTAGNOLI_POLY);
let table16 = make_table16(CASTAGNOLI_POLY);
writeln!(out, "pub const TABLE: [u32; 256] = [")?;
for &x in table.iter() {
writeln!(out, " {},", x)?;
}
writeln!(out, "];\n")?;
writeln!(out, "pub const TABLE16: [[u32; 256]; 16] = [")?;
for table in table16.iter() {
writeln!(out, " [")?;
for &x in table.iter() {
writeln!(out, " {},", x)?;
}
writeln!(out, " ],")?;
}
writeln!(out, "];")?;
out.flush()?;
Ok(())
}
fn make_table16(poly: u32) -> [[u32; 256]; 16] {
let mut tab = [[0; 256]; 16];
tab[0] = make_table(poly);
for i in 0..256 {
let mut crc = tab[0][i];
for j in 1..16 {
crc = (crc >> 8) ^ tab[0][crc as u8 as usize];
tab[j][i] = crc;
}
}
tab
}
fn make_table(poly: u32) -> [u32; 256] {
let mut tab = [0; 256];
for i in 0u32..256u32 {
let mut crc = i;
for _ in 0..8 {
if crc & 1 == 1 {
crc = (crc >> 1) ^ poly;
} else {
crc >>= 1;
}
}
tab[i as usize] = crc;
}
tab
}
|
