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only use fma intrinsics if fma is enabled #44805

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only use fma intrinsics if fma is enabled #44805

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2d1589a
only use the fmaf32 and fmaf64 intrinsics if `fma` is enabled
Sep 24, 2017
ec574c4
use if cfg!(...) instead of #[cfg(...)]
Sep 24, 2017
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9 changes: 8 additions & 1 deletion src/libstd/f32.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -395,6 +395,9 @@ impl f32 {
/// error. This produces a more accurate result with better performance than
/// a separate multiplication operation followed by an add.
///
/// This will fall back to computing `(self * a) + b` if the target-feature `fma`
/// is not enabled.
///
/// ```
/// use std::f32;
///
Expand All @@ -410,7 +413,11 @@ impl f32 {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn mul_add(self, a: f32, b: f32) -> f32 {
unsafe { intrinsics::fmaf32(self, a, b) }
if cfg!(target_feature="fma") {
unsafe { intrinsics::fmaf32(self, a, b) }
} else {
self * a + b
}
}

/// Takes the reciprocal (inverse) of a number, `1/x`.
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9 changes: 8 additions & 1 deletion src/libstd/f64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -343,6 +343,9 @@ impl f64 {
/// error. This produces a more accurate result with better performance than
/// a separate multiplication operation followed by an add.
///
/// This will fall back to computing `(self * a) + b` if the target-feature `fma`
/// is not enabled.
///
/// ```
/// let m = 10.0_f64;
/// let x = 4.0_f64;
Expand All @@ -356,7 +359,11 @@ impl f64 {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn mul_add(self, a: f64, b: f64) -> f64 {
unsafe { intrinsics::fmaf64(self, a, b) }
if cfg!(target_feature="fma") {
unsafe { intrinsics::fmaf64(self, a, b) }
} else {
self * a + b
}
}

/// Takes the reciprocal (inverse) of a number, `1/x`.
Expand Down