Add a libm feature for Float

.travis.yml

@@ -19,15 +19,15 @@ matrix:
       before_script:
         - rustup target add $TARGET
       script:
-        - cargo build --verbose --target $TARGET --no-default-features --features "alloc serde rand"
+        - cargo build --verbose --target $TARGET --no-default-features --features "alloc libm serde rand"
     # try a target that doesn't have std at all, nor alloc
     - name: "no_std"
       rust: 1.31.0
       env: TARGET=thumbv6m-none-eabi
       before_script:
         - rustup target add $TARGET
       script:
-        - cargo build --verbose --target $TARGET --no-default-features
+        - cargo build --verbose --target $TARGET --no-default-features --features libm
     - name: "rustfmt"
       rust: 1.31.0
       before_script:

Cargo.toml

@@ -69,6 +69,11 @@ std = [
 
 alloc = ["num-bigint", "num-rational/bigint"]
 
+libm = [
+  "num-complex/libm",
+  "num-traits/libm",
+]
+
 rand = [
   "num-bigint/rand",
   "num-complex/rand",

README.md

@@ -50,6 +50,9 @@ The `num-bigint` crate requires the `std` feature, or the `alloc` feature may
 be used instead with Rust 1.36 and later. Other sub-crates may also have
 limited functionality when used without `std`.
 
+The `libm` feature uses pure-Rust floating point implementations in `no_std`
+builds, enabling the `Float` trait and related `Complex` methods.
+
 The `rand` feature enables randomization traits in `num-bigint` and
 `num-complex`.
 

ci/test_full.sh

@@ -5,15 +5,17 @@ set -ex
 echo Testing num on rustc ${TRAVIS_RUST_VERSION}
 
 case "$TRAVIS_RUST_VERSION" in
-  1.31.*) STD_FEATURES="serde" ;;
-  *) STD_FEATURES="serde rand" ;;
+  1.31.*) STD_FEATURES="libm serde" ;;
+  *) STD_FEATURES="libm serde rand" ;;
 esac
 
 case "$TRAVIS_RUST_VERSION" in
   1.3[1-5].*) ;;
-  *) ALLOC_FEATURES="serde rand" ;;
+  *) ALLOC_FEATURES="libm serde rand" ;;
 esac
 
+NO_STD_FEATURES="libm"
+
 # num should build and test everywhere.
 cargo build --verbose
 cargo test --verbose
@@ -48,3 +50,15 @@ if test -n "${ALLOC_FEATURES:+true}"; then
   cargo build --no-default-features --features="alloc $ALLOC_FEATURES"
   cargo test --no-default-features --features="alloc $ALLOC_FEATURES"
 fi
+
+if test -n "${NO_STD_FEATURES:+true}"; then
+  # Each isolated feature should also work everywhere.
+  for feature in $NO_STD_FEATURES; do
+    cargo build --verbose --no-default-features --features="$feature"
+    cargo test --verbose --no-default-features --features="$feature"
+  done
+
+  # test all supported features together
+  cargo build --no-default-features --features="$NO_STD_FEATURES"
+  cargo test --no-default-features --features="$NO_STD_FEATURES"
+fi

src/lib.rs

@@ -72,7 +72,7 @@ pub use num_integer::Integer;
 
 pub use num_iter::{range, range_inclusive, range_step, range_step_inclusive};
 
-#[cfg(feature = "std")]
+#[cfg(any(feature = "libm", feature = "std"))]
 pub use num_traits::Float;
 pub use num_traits::{
     abs, abs_sub, cast, checked_pow, clamp, one, pow, signum, zero, Bounded, CheckedAdd,