Update example.

Author: calder

library/core/src/primitive_docs.rs

@@ -1326,9 +1326,10 @@ mod prim_f16 {}
 /// This can give a great performance boost since it may unlock vectorization.
 ///
 /// The exact set of optimizations is unspecified but typically allows combining operations,
-/// rearranging series of operations based on mathematical properties, converting between division and reciprocal multiplication, and
-/// disregarding the sign of zero. This means that the results of elementary operations may have
-/// undefined precision, but will not invoke input-dependent undefined behavior.
+/// rearranging series of operations based on mathematical properties, converting between division
+/// and reciprocal multiplication, and disregarding the sign of zero. This means that the results of
+/// elementary operations may have undefined precision, but will not invoke input-dependent
+/// undefined behavior.
 ///
 /// Because of the unpredictable nature of compiler optimizations, the same inputs may produce
 /// different results even within a single program run. **Unsafe code must not rely on any property
@@ -1340,21 +1341,25 @@ mod prim_f16 {}
 /// ```
 /// # #![feature(float_algebraic)]
 /// # #![allow(unused_assignments)]
-/// # let mut x: f32 = 12.0;
-/// # let a: f32 = 34.0;
-/// # let b: f32 = 56.0;
-/// x = x.algebraic_add(a.algebraic_mul(b));
+/// # let mut x: f32 = 0.0;
+/// # let a: f32 = 1.0;
+/// # let b: f32 = 2.0;
+/// # let b: f32 = 3.0;
+/// # let b: f32 = 4.0;
+/// x = a.algebraic_add(b).algebraic_add(c).algebraic_add(d);
 /// ```
 ///
 /// May be rewritten as either:
 ///
 /// ```
 /// # #![allow(unused_assignments)]
-/// # let mut x: f32 = 12.0;
-/// # let a: f32 = 34.0;
-/// # let b: f32 = 56.0;
-/// x = x + (a * b); // As written
-/// x = (a * b) + x; // Reordered to allow using a single `fma`
+/// # let mut x: f32 = 0.0;
+/// # let a: f32 = 1.0;
+/// # let b: f32 = 2.0;
+/// # let b: f32 = 3.0;
+/// # let b: f32 = 4.0;
+/// x = a + b + c + d; // As written
+/// x = (a + c) + (b + d); // Reordered to shorten critical path and enable vectorization
 /// ```
 
 #[stable(feature = "rust1", since = "1.0.0")]