feat: no_std support

* no_std support

* Use integer log2 when possible to estimate allocations

* Remove std features from a few dependencies

* Use libm for missing funcs in nostd environment

* Use autocfg to detect presence of i128

* Better CI test for nostd environment

* Move benchmark to a separate crate

* Make the tests pass in no_std builds

* Use thumbv7m target for nostd build test

* Add documentation about the no-std compatibility

* Make zeroize and prime features no_std-compatible

* Test each feature in nostd context

* Fix mac test to work in no_std environment

* Avoid using thread_rng in nostd tests

* Fix prime tests in nostd mode

* Fix all warnings and errors

* Only test nostd builds on nightly on travis

* Travis: Only do nostd builds on nightly

Cargo.toml

@@ -16,11 +16,6 @@ autobenches = false
 [package.metadata.docs.rs]
 features = ["std", "serde", "rand", "prime"]
 
-[[bench]]
-harness = false
-name = "bench_main"
-required-features = ["prime"]
-
 [dependencies]
 
 [dependencies.smallvec]
@@ -43,37 +38,47 @@ default-features = false
 optional = true
 version = "0.6"
 default-features = false
-features = ["std"]
 
 [dependencies.zeroize]
 version = "0.6"
 optional = true
+default-features = false
+features = ["zeroize_derive"]
 
 [dependencies.serde]
 optional = true
 version = "1.0"
 default-features = false
-features = ["std"]
+
+[dependencies.libm]
+version = "0.1.4"
 
 [dependencies.lazy_static]
 version = "1.2.0"
+default-features = false
+# no_std feature is an anti-pattern. Why, lazy_static, why?
+# See https://github.com/rust-lang-nursery/lazy-static.rs/issues/150
+features = ["spin_no_std"]
 
 [dependencies.byteorder]
 version = "1.2.7"
+default-features = false
 
 [dev-dependencies]
-criterion = "0.2"
 rand_chacha = "0.1"
 rand_xorshift = "0.1"
 rand_isaac = "0.1"
 
+[build-dependencies]
+autocfg = "0.1.5"
+
 [dev-dependencies.serde_test]
 version = "1.0"
 
 [features]
 default = ["std", "i128", "u64_digit"]
 i128 = ["num-integer/i128", "num-traits/i128"]
-std = ["num-integer/std", "num-traits/std", "smallvec/std", "rand/std"]
+std = ["num-integer/std", "num-traits/std", "smallvec/std", "rand/std", "serde/std", "zeroize/std"]
 u64_digit = []
 prime = ["rand"]
 nightly = ["zeroize/nightly", "rand/nightly"]

README.md

@@ -26,10 +26,14 @@ extern crate num_bigint_dig as num_bigint;
 
 ## Features
 
-The `std` crate feature is mandatory and enabled by default.  If you depend on
-`num-bigint` with `default-features = false`, you must manually enable the
-`std` feature yourself.  In the future, we hope to support `#![no_std]` with
-the `alloc` crate when `std` is not enabled.
+The `std` feature is enabled by default and mandatory to compile on older rust
+version.
+
+On Rust 1.36 and later, it is possible to use this crate on no_std target. If
+you wish to compile for a target that does not have an `std` crate, you should
+use `num-bigint` with `default-features = false`. All other sub-features should
+be compatible with no_std. Note that in this mode, `num-bigint` still relies on
+the alloc crate, so make sure you define a `global_allocator`.
 
 Implementations for `i128` and `u128` are only available with Rust 1.26 and
 later.  The build script automatically detects this, but you can make it

benchmark_crate/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "num-bigint-dig-benchmark"
+version = "0.0.0"
+autobenches = false
+publish = false
+
+[[bench]]
+harness = false
+name = "bench_main"
+
+[dependencies]
+num-bigint-dig = { path = "../", features = ["prime", "rand"] }
+num-integer = "0.1.39"
+num-traits = "0.2.4"
+rand = "0.6"
+rand_chacha = "0.1"
+
+[dev-dependencies]
+criterion = "0.2"

benches/benchmarks/roots.rs → benchmark_crate/benches/benchmarks/roots.rs

@@ -1,5 +1,3 @@
-#![cfg(feature = "rand")]
-
 use criterion::Criterion;
 use num_bigint::{BigUint, RandBigInt};
 use num_traits::Pow;

build.rs

@@ -1,35 +1,12 @@
+extern crate autocfg;
 use std::env;
-use std::io::Write;
-use std::process::{Command, Stdio};
 
 fn main() {
-    if probe("fn main() { 0i128; }") {
+    let ac = autocfg::new();
+
+    if ac.probe_type("i128") {
         println!("cargo:rustc-cfg=has_i128");
     } else if env::var_os("CARGO_FEATURE_I128").is_some() {
         panic!("i128 support was not detected!");
     }
-}
-
-/// Test if a code snippet can be compiled
-fn probe(code: &str) -> bool {
-    let rustc = env::var_os("RUSTC").unwrap_or_else(|| "rustc".into());
-    let out_dir = env::var_os("OUT_DIR").expect("environment variable OUT_DIR");
-
-    let mut child = Command::new(rustc)
-        .arg("--out-dir")
-        .arg(out_dir)
-        .arg("--emit=obj")
-        .arg("-")
-        .stdin(Stdio::piped())
-        .spawn()
-        .expect("rustc probe");
-
-    child
-        .stdin
-        .as_mut()
-        .expect("rustc stdin")
-        .write_all(code.as_bytes())
-        .expect("write rustc stdin");
-
-    child.wait().expect("rustc probe").success()
-}
+}

ci/test_full.sh

@@ -16,10 +16,27 @@ cargo test --verbose
 cargo build --no-default-features --features="std"
 cargo test --no-default-features --features="std"
 
+# It should build in no_std
+if [[ "$TRAVIS_RUST_VERSION" == "nightly" ]]; then
+  rustup target add thumbv7m-none-eabi
+  cargo build --no-default-features --target=thumbv7m-none-eabi
+
+  # It should work in no_std on nightly.
+  # Note: Doctest might show an error: https://github.com/rust-lang/rust/issues/54010
+  # The "error" is wrong however, the doctests still run.
+  cargo test --no-default-features
+fi
+
 # Each isolated feature should also work everywhere.
 for feature in $FEATURES; do
   cargo build --verbose --no-default-features --features="std $feature"
   cargo test --verbose --no-default-features --features="std $feature"
+
+  # Ensure that feature also works in nostd context on nightly.
+  if [[ "$TRAVIS_RUST_VERSION" == "nightly" ]]; then
+    cargo build --verbose --no-default-features --features="$feature"
+    cargo test --verbose --no-default-features --features="$feature"
+  fi
 done
 
 # test all supported features together
@@ -28,5 +45,6 @@ cargo test --features="std $FEATURES"
 
 # make sure benchmarks can be built
 if [[ "$TRAVIS_RUST_VERSION" == "nightly" ]]; then
+  cd benchmark_crate
   cargo bench --all-features --no-run
 fi

src/algorithms/bits.rs

@@ -1,4 +1,4 @@
-use std::mem;
+use core::mem;
 
 /// Find last set bit
 /// fls(0) == 0, fls(u32::MAX) == 32
@@ -9,3 +9,12 @@ pub fn fls<T: num_traits::PrimInt>(v: T) -> usize {
 pub fn ilog2<T: num_traits::PrimInt>(v: T) -> usize {
     fls(v) - 1
 }
+
+/// Divide two integers, and ceil the result.
+pub fn idiv_ceil<T: num_traits::PrimInt>(a: T, b: T) -> T {
+    if a % b != T::zero() {
+        a / b + T::one()
+    } else {
+        a / b
+    }
+}

src/algorithms/cmp.rs

@@ -1,4 +1,4 @@
-use std::cmp::Ordering::{self, Equal, Greater, Less};
+use core::cmp::Ordering::{self, Equal, Greater, Less};
 
 use crate::big_digit::BigDigit;
 

src/algorithms/div.rs

@@ -1,6 +1,6 @@
 use num_traits::{One, Zero};
 use smallvec::SmallVec;
-use std::cmp::Ordering;
+use core::cmp::Ordering;
 
 use crate::algorithms::{add2, cmp_slice, sub2};
 use crate::big_digit::{self, BigDigit, DoubleBigDigit};

src/algorithms/gcd.rs

@@ -4,8 +4,8 @@ use crate::bigint::{BigInt, ToBigInt};
 use crate::biguint::{BigUint, IntDigits};
 use integer::Integer;
 use num_traits::{One, Signed, Zero};
-use std::borrow::Cow;
-use std::ops::Neg;
+use alloc::borrow::Cow;
+use core::ops::Neg;
 
 /// XGCD sets z to the greatest common divisor of a and b and returns z.
 /// If extended is true, XGCD returns their value such that z = a*x + b*y.
@@ -98,8 +98,8 @@ fn lehmer_gcd(
 
     // Ensure that a >= b
     if a < b {
-        std::mem::swap(&mut a, &mut b);
-        std::mem::swap(&mut ua, &mut ub);
+        core::mem::swap(&mut a, &mut b);
+        core::mem::swap(&mut ua, &mut ub);
     }
 
     // loop invariant A >= B
@@ -277,8 +277,8 @@ pub fn extended_gcd(
 
     // Ensure that a >= b
     if a < b {
-        std::mem::swap(&mut a, &mut b);
-        std::mem::swap(&mut ua, &mut ub);
+        core::mem::swap(&mut a, &mut b);
+        core::mem::swap(&mut ua, &mut ub);
     }
 
     let mut q: BigInt = 0.into();
@@ -527,8 +527,8 @@ fn euclid_udpate(
     *q = q_new;
     *r = r_new;
 
-    std::mem::swap(a, b);
-    std::mem::swap(b, r);
+    core::mem::swap(a, b);
+    core::mem::swap(b, r);
 
     if extended {
         // ua, ub = ub, ua - q * ub
@@ -546,7 +546,7 @@ fn euclid_udpate(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::str::FromStr;
+    use core::str::FromStr;
 
     use num_traits::FromPrimitive;
 
@@ -574,11 +574,11 @@ mod tests {
         while !r.is_zero() {
             let quotient = &old_r / &r;
             old_r = old_r - &quotient * &r;
-            std::mem::swap(&mut old_r, &mut r);
+            core::mem::swap(&mut old_r, &mut r);
             old_s = old_s - &quotient * &s;
-            std::mem::swap(&mut old_s, &mut s);
+            core::mem::swap(&mut old_s, &mut s);
             old_t = old_t - quotient * &t;
-            std::mem::swap(&mut old_t, &mut t);
+            core::mem::swap(&mut old_t, &mut t);
         }
 
         (old_r, old_s, old_t)

src/algorithms/mac.rs

@@ -1,5 +1,5 @@
-use std::cmp;
-use std::iter::repeat;
+use core::cmp;
+use core::iter::repeat;
 
 use crate::algorithms::{adc, add2, sub2, sub_sign};
 use crate::big_digit::{BigDigit, DoubleBigDigit, BITS};
@@ -310,7 +310,7 @@ mod tests {
     #[cfg(feature = "u64_digit")]
     #[test]
     fn test_mac3_regression() {
-        let b: Vec<BigDigit> = vec![
+        let b = [
             6871754923702299421,
             18286959765922425554,
             16443042141374662930,
@@ -657,7 +657,7 @@ mod tests {
             17511662813348858473,
             12,
         ];
-        let c: Vec<BigDigit> = vec![
+        let c = [
             13147625290258353449,
             13817956093586917764,
             18028234882233861888,
@@ -1655,18 +1655,18 @@ mod tests {
             1305238720762,
         ];
 
-        let mut a1: Vec<BigDigit> = vec![0; 1341];
-        let mut a2: Vec<BigDigit> = vec![0; 1341];
-        let mut a3: Vec<BigDigit> = vec![0; 1341];
+        let mut a1 = &mut [0; 1341];
+        let mut a2 = &mut [0; 1341];
+        let mut a3 = &mut [0; 1341];
 
         //print!("{} {}", b.len(), c.len());
-        long(&mut a1, &b, &c);
-        karatsuba(&mut a2, &b, &c);
+        long(a1, &b, &c);
+        karatsuba(a2, &b, &c);
 
-        assert_eq!(a1, a2);
+        assert_eq!(&a1[..], &a2[..]);
 
         // println!("res: {:?}", &a1);
-        toom3(&mut a3, &b, &c);
-        assert_eq!(a1, a3);
+        toom3(a3, &b, &c);
+        assert_eq!(&a1[..], &a3[..]);
     }
 }

src/algorithms/mod_inverse.rs

@@ -1,4 +1,4 @@
-use std::borrow::Cow;
+use alloc::borrow::Cow;
 
 use num_traits::{One, Signed};
 

src/algorithms/shl.rs

@@ -1,5 +1,5 @@
-use std::borrow::Cow;
-use std::iter::repeat;
+use alloc::borrow::Cow;
+use core::iter::repeat;
 
 use smallvec::SmallVec;
 

src/algorithms/shr.rs

@@ -1,4 +1,4 @@
-use std::borrow::Cow;
+use alloc::borrow::Cow;
 
 use num_traits::Zero;
 use smallvec::SmallVec;

src/algorithms/sub.rs

@@ -1,5 +1,5 @@
-use std::cmp;
-use std::cmp::Ordering::*;
+use core::cmp;
+use core::cmp::Ordering::*;
 
 use num_traits::Zero;
 use smallvec::SmallVec;