1 use std::env;
2 use std::error::Error;
3 use std::fs::File;
4 use std::io::Write;
5 use std::path::Path;
6
main()7 fn main() {
8 let pointer_width = env::var("CARGO_CFG_TARGET_POINTER_WIDTH");
9 if pointer_width.as_ref().map(String::as_str) == Ok("64") {
10 autocfg::emit("u64_digit");
11 }
12 let ac = autocfg::new();
13 if ac.probe_path("std::convert::TryFrom") || ac.probe_path("core::convert::TryFrom") {
14 autocfg::emit("has_try_from");
15 }
16
17 autocfg::rerun_path("build.rs");
18
19 write_radix_bases().unwrap();
20 }
21
22 /// Write tables of the greatest power of each radix for the given bit size. These are returned
23 /// from `biguint::get_radix_base` to batch the multiplication/division of radix conversions on
24 /// full `BigUint` values, operating on primitive integers as much as possible.
25 ///
26 /// e.g. BASES_16[3] = (59049, 10) // 3¹⁰ fits in u16, but 3¹¹ is too big
27 /// BASES_32[3] = (3486784401, 20)
28 /// BASES_64[3] = (12157665459056928801, 40)
29 ///
30 /// Powers of two are not included, just zeroed, as they're implemented with shifts.
write_radix_bases() -> Result<(), Box<dyn Error>>31 fn write_radix_bases() -> Result<(), Box<dyn Error>> {
32 let out_dir = env::var("OUT_DIR")?;
33 let dest_path = Path::new(&out_dir).join("radix_bases.rs");
34 let mut f = File::create(&dest_path)?;
35
36 for &bits in &[16, 32, 64] {
37 let max = if bits < 64 {
38 (1 << bits) - 1
39 } else {
40 std::u64::MAX
41 };
42
43 writeln!(f, "#[deny(overflowing_literals)]")?;
44 writeln!(
45 f,
46 "pub(crate) static BASES_{bits}: [(u{bits}, usize); 257] = [",
47 bits = bits
48 )?;
49 for radix in 0u64..257 {
50 let (base, power) = if radix == 0 || radix.is_power_of_two() {
51 (0, 0)
52 } else {
53 let mut power = 1;
54 let mut base = radix;
55
56 while let Some(b) = base.checked_mul(radix) {
57 if b > max {
58 break;
59 }
60 base = b;
61 power += 1;
62 }
63 (base, power)
64 };
65 writeln!(f, " ({}, {}), // {}", base, power, radix)?;
66 }
67 writeln!(f, "];")?;
68 }
69
70 Ok(())
71 }
72