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Add a feature to enforce libm in std environment #375

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1eda4f0
Add a `force-libm` feature
ElouanPetereau Feb 9, 2026
de1f523
Modify test script to also test the `force-libm` feature
ElouanPetereau Feb 10, 2026
791f25c
Update full test ci script with libm-force validation
ElouanPetereau Mar 3, 2026
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1 change: 1 addition & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ libm = { version = "0.2.0", optional = true }
default = ["std"]
libm = ["dep:libm"]
std = []
force-libm = ["libm"]

# vestigial features, now always in effect
i128 = []
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22 changes: 21 additions & 1 deletion ci/test_full.sh
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Expand Up @@ -27,7 +27,7 @@ if ! check_version $MSRV ; then
exit 1
fi

FEATURES=(libm)
FEATURES=(libm force-libm)
echo "Testing supported features: ${FEATURES[*]}"

cargo generate-lockfile
Expand Down Expand Up @@ -58,3 +58,23 @@ cargo test --features="std ${FEATURES[*]}"

cargo build --features="${FEATURES[*]}"
cargo test --features="${FEATURES[*]}"

# Verify that `force-libm` feature actually switches the math implementation
# by checking for libm symbols in the linked test binary.
get_test_binary() {
cargo test --no-run --no-default-features --features="$1" --message-format=json 2>/dev/null \
| grep '"name":"num_traits"' \
| sed -n 's/.*"executable":"\([^"]*\)".*/\1/p'
}

echo "Checking that test binary built with only the 'std' feature DOES NOT contain libm math symbols..."
if nm -C "$(get_test_binary "std")" | grep -q 'libm::math'; then
echo "force-libm symbol check failed: std-only binary should not contain libm math symbols"
exit 1
fi

echo "Checking that test binary built with 'std' and 'force-libm' features DOES contain libm math symbols..."
if ! nm -C "$(get_test_binary "std,force-libm")" | grep -q 'libm::math'; then
echo "force-libm symbol check failed: force-libm binary should contain libm math symbols"
exit 1
fi
24 changes: 12 additions & 12 deletions src/float.rs
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Expand Up @@ -832,7 +832,7 @@ impl FloatCore for f32 {
Self::to_radians(self) -> Self;
}

#[cfg(feature = "std")]
#[cfg(all(feature = "std", not(feature = "force-libm")))]
forward! {
Self::floor(self) -> Self;
Self::ceil(self) -> Self;
Expand All @@ -844,7 +844,7 @@ impl FloatCore for f32 {
Self::powi(self, n: i32) -> Self;
}

#[cfg(all(not(feature = "std"), feature = "libm"))]
#[cfg(any(feature = "force-libm", all(not(feature = "std"), feature = "libm")))]
forward! {
libm::floorf as floor(self) -> Self;
libm::ceilf as ceil(self) -> Self;
Expand All @@ -853,7 +853,7 @@ impl FloatCore for f32 {
libm::fabsf as abs(self) -> Self;
}

#[cfg(all(not(feature = "std"), feature = "libm"))]
#[cfg(any(feature = "force-libm", all(not(feature = "std"), feature = "libm")))]
#[inline]
fn fract(self) -> Self {
self - libm::truncf(self)
Expand Down Expand Up @@ -894,7 +894,7 @@ impl FloatCore for f64 {
Self::to_radians(self) -> Self;
}

#[cfg(feature = "std")]
#[cfg(all(feature = "std", not(feature = "force-libm")))]
forward! {
Self::floor(self) -> Self;
Self::ceil(self) -> Self;
Expand All @@ -906,7 +906,7 @@ impl FloatCore for f64 {
Self::powi(self, n: i32) -> Self;
}

#[cfg(all(not(feature = "std"), feature = "libm"))]
#[cfg(any(feature = "force-libm", all(not(feature = "std"), feature = "libm")))]
forward! {
libm::floor as floor(self) -> Self;
libm::ceil as ceil(self) -> Self;
Expand All @@ -915,7 +915,7 @@ impl FloatCore for f64 {
libm::fabs as abs(self) -> Self;
}

#[cfg(all(not(feature = "std"), feature = "libm"))]
#[cfg(any(feature = "force-libm", all(not(feature = "std"), feature = "libm")))]
#[inline]
fn fract(self) -> Self {
self - libm::trunc(self)
Expand Down Expand Up @@ -1911,7 +1911,7 @@ pub trait Float: Num + Copy + NumCast + PartialOrd + Neg<Output = Self> {
}
}

#[cfg(feature = "std")]
#[cfg(all(feature = "std", not(feature = "force-libm")))]
macro_rules! float_impl_std {
($T:ident $decode:ident) => {
impl Float for $T {
Expand Down Expand Up @@ -1993,7 +1993,7 @@ macro_rules! float_impl_std {
};
}

#[cfg(all(not(feature = "std"), feature = "libm"))]
#[cfg(any(feature = "force-libm", all(not(feature = "std"), feature = "libm")))]
macro_rules! float_impl_libm {
($T:ident $decode:ident) => {
constant! {
Expand Down Expand Up @@ -2074,12 +2074,12 @@ fn integer_decode_f64(f: f64) -> (u64, i16, i8) {
(mantissa, exponent, sign)
}

#[cfg(feature = "std")]
#[cfg(all(feature = "std", not(feature = "force-libm")))]
float_impl_std!(f32 integer_decode_f32);
#[cfg(feature = "std")]
#[cfg(all(feature = "std", not(feature = "force-libm")))]
float_impl_std!(f64 integer_decode_f64);

#[cfg(all(not(feature = "std"), feature = "libm"))]
#[cfg(any(feature = "force-libm", all(not(feature = "std"), feature = "libm")))]
impl Float for f32 {
float_impl_libm!(f32 integer_decode_f32);

Expand Down Expand Up @@ -2125,7 +2125,7 @@ impl Float for f32 {
}
}

#[cfg(all(not(feature = "std"), feature = "libm"))]
#[cfg(any(feature = "force-libm", all(not(feature = "std"), feature = "libm")))]
impl Float for f64 {
float_impl_libm!(f64 integer_decode_f64);

Expand Down
2 changes: 1 addition & 1 deletion src/lib.rs
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Expand Up @@ -380,7 +380,7 @@ macro_rules! float_trait_impl {
None => return Err(PFE { kind: Invalid }),
};

#[cfg(feature = "std")]
#[cfg(all(feature = "std", not(feature = "force-libm")))]
fn pow(base: $t, exp: usize) -> $t {
Float::powi(base, exp as i32)
}
Expand Down
6 changes: 3 additions & 3 deletions src/ops/euclid.rs
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Expand Up @@ -88,10 +88,10 @@ macro_rules! euclid_forward_impl {
euclid_forward_impl!(isize i8 i16 i32 i64 i128);
euclid_forward_impl!(usize u8 u16 u32 u64 u128);

#[cfg(feature = "std")]
#[cfg(all(feature = "std", not(feature = "force-libm")))]
euclid_forward_impl!(f32 f64);

#[cfg(not(feature = "std"))]
#[cfg(any(feature = "force-libm", not(feature = "std")))]
impl Euclid for f32 {
#[inline]
fn div_euclid(&self, v: &f32) -> f32 {
Expand All @@ -113,7 +113,7 @@ impl Euclid for f32 {
}
}

#[cfg(not(feature = "std"))]
#[cfg(any(feature = "force-libm", not(feature = "std")))]
impl Euclid for f64 {
#[inline]
fn div_euclid(&self, v: &f64) -> f64 {
Expand Down