scripts: remove Python script in favor of build.rs

No particular reason to do this other than to remove a dependency on
Python. I don't think this was done originally purely because snap
existed before build.rs was I thing (I think).

build.rs

@@ -1,23 +1,72 @@
 use std::env;
 use std::fs::File;
 use std::io::{self, Write};
-use std::path::PathBuf;
+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<(), Box<dyn std::error::Error>> {
+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)?);
 

src/tag.rs

@@ -1,35 +1,2 @@
-// DO NOT EDIT THIS FILE!
-// IT IS AUTOMATICALLY GENERATED BY scripts/gen-tag-lookup-table
-// Generated at 2016-07-16 11:48:48.881229
-
-pub const TAG_LOOKUP_TABLE: [u16; 256] = [
-    0x0001, 0x0804, 0x1001, 0x2001, 0x0002, 0x0805, 0x1002, 0x2002, 0x0003,
-    0x0806, 0x1003, 0x2003, 0x0004, 0x0807, 0x1004, 0x2004, 0x0005, 0x0808,
-    0x1005, 0x2005, 0x0006, 0x0809, 0x1006, 0x2006, 0x0007, 0x080a, 0x1007,
-    0x2007, 0x0008, 0x080b, 0x1008, 0x2008, 0x0009, 0x0904, 0x1009, 0x2009,
-    0x000a, 0x0905, 0x100a, 0x200a, 0x000b, 0x0906, 0x100b, 0x200b, 0x000c,
-    0x0907, 0x100c, 0x200c, 0x000d, 0x0908, 0x100d, 0x200d, 0x000e, 0x0909,
-    0x100e, 0x200e, 0x000f, 0x090a, 0x100f, 0x200f, 0x0010, 0x090b, 0x1010,
-    0x2010, 0x0011, 0x0a04, 0x1011, 0x2011, 0x0012, 0x0a05, 0x1012, 0x2012,
-    0x0013, 0x0a06, 0x1013, 0x2013, 0x0014, 0x0a07, 0x1014, 0x2014, 0x0015,
-    0x0a08, 0x1015, 0x2015, 0x0016, 0x0a09, 0x1016, 0x2016, 0x0017, 0x0a0a,
-    0x1017, 0x2017, 0x0018, 0x0a0b, 0x1018, 0x2018, 0x0019, 0x0b04, 0x1019,
-    0x2019, 0x001a, 0x0b05, 0x101a, 0x201a, 0x001b, 0x0b06, 0x101b, 0x201b,
-    0x001c, 0x0b07, 0x101c, 0x201c, 0x001d, 0x0b08, 0x101d, 0x201d, 0x001e,
-    0x0b09, 0x101e, 0x201e, 0x001f, 0x0b0a, 0x101f, 0x201f, 0x0020, 0x0b0b,
-    0x1020, 0x2020, 0x0021, 0x0c04, 0x1021, 0x2021, 0x0022, 0x0c05, 0x1022,
-    0x2022, 0x0023, 0x0c06, 0x1023, 0x2023, 0x0024, 0x0c07, 0x1024, 0x2024,
-    0x0025, 0x0c08, 0x1025, 0x2025, 0x0026, 0x0c09, 0x1026, 0x2026, 0x0027,
-    0x0c0a, 0x1027, 0x2027, 0x0028, 0x0c0b, 0x1028, 0x2028, 0x0029, 0x0d04,
-    0x1029, 0x2029, 0x002a, 0x0d05, 0x102a, 0x202a, 0x002b, 0x0d06, 0x102b,
-    0x202b, 0x002c, 0x0d07, 0x102c, 0x202c, 0x002d, 0x0d08, 0x102d, 0x202d,
-    0x002e, 0x0d09, 0x102e, 0x202e, 0x002f, 0x0d0a, 0x102f, 0x202f, 0x0030,
-    0x0d0b, 0x1030, 0x2030, 0x0031, 0x0e04, 0x1031, 0x2031, 0x0032, 0x0e05,
-    0x1032, 0x2032, 0x0033, 0x0e06, 0x1033, 0x2033, 0x0034, 0x0e07, 0x1034,
-    0x2034, 0x0035, 0x0e08, 0x1035, 0x2035, 0x0036, 0x0e09, 0x1036, 0x2036,
-    0x0037, 0x0e0a, 0x1037, 0x2037, 0x0038, 0x0e0b, 0x1038, 0x2038, 0x0039,
-    0x0f04, 0x1039, 0x2039, 0x003a, 0x0f05, 0x103a, 0x203a, 0x003b, 0x0f06,
-    0x103b, 0x203b, 0x003c, 0x0f07, 0x103c, 0x203c, 0x0800, 0x0f08, 0x103d,
-    0x203d, 0x1000, 0x0f09, 0x103e, 0x203e, 0x1800, 0x0f0a, 0x103f, 0x203f,
-    0x2000, 0x0f0b, 0x1040, 0x2040,
-];
+// Generated by build.rs.
+include!(concat!(env!("OUT_DIR"), "/tag.rs"));