Remove from_f32(...) and note that the type can only be constructed through vendor intrinsics

Author: Jamesbarford

text/3983-bf16.md

@@ -72,25 +72,12 @@ Alternatively, some other compiler magic could map the struct to LLVM's `bfloat`
 ```rust
 impl bf16 {
     pub const fn from_bits(bits: u16) -> bf16;
-    pub const fn from_f32(flt: f32) -> bf16;
     pub const fn to_bits(self) -> u16;
 }
 ```
 
-Where `from_f32` would allow instantiating a `bf16` and could look something like the following;
+Constructing a `bf16` can intially only be done through either `bf16::from_bits(...)` or vendor intrinsics.
 
-```rust
-// in the `impl bf16 {` block
-pub fn from_f32(flt: f32) -> Self {
-    let bits = flt.to_bits();
-    if bits & 0x7FFF_FFFF > 0x7F80_0000 {
-        return Self(((bits >> 16) as u16) | 0x0040);
-    }
-    let retained_lsb = (bits >> 16) & 1;
-    let rounding_bias = 0x7FFF + retained_lsb;
-    Self((bits.wrapping_add(rounding_bias) >> 16) as u16)
-}
-```
 
 ### Implemented Traits
 [implemented-traits]: #implemented-traits