Auto merge of #138363 - beetrees:f16-f128-integer-convert, r=Amanieu

Add `From<{integer}>` for `f16`/`f128` impls

This PR adds `impl From<{bool,i8,u8}> for f16` and `impl From<{bool,i8,u8,i16,u16,i32,u32}> for f128`.

The `From<{i64,u64}> for f128` impls are left commented out as adding them would allow using `f128` on stable before it is stabilised like in the following example:
```rust
fn f<T: From<u64>>(x: T) -> T { x }

fn main() {
    let x = f(1.0); // the type of the literal is inferred to be `f128`
}
```
None of the impls added in this PR have this issue as they are all, at minimum, also implemented by `f64`.

This PR will need a crater run for the `From<{i32,u32}>` impls, as `f64` is no longer the only float type to implement them (similar to the cause of #125198).

cc `@bjoernager`
r? `@tgross35`

Tracking issue: #116909

2 files changed, 43 insertions, 0 deletions

diff --git a/library/std/tests/floats/f128.rs b/library/std/tests/floats/f128.rs
index d0e8b157e6b..b4a6c672bf0 100644
--- a/library/std/tests/floats/f128.rs
+++ b/library/std/tests/floats/f128.rs
@@ -983,3 +983,34 @@ fn test_total_cmp() {
     assert_eq!(Ordering::Less, (-s_nan()).total_cmp(&f128::INFINITY));
     assert_eq!(Ordering::Less, (-s_nan()).total_cmp(&s_nan()));
 }
+
+#[test]
+fn test_from() {
+    assert_eq!(f128::from(false), 0.0);
+    assert_eq!(f128::from(true), 1.0);
+    assert_eq!(f128::from(u8::MIN), 0.0);
+    assert_eq!(f128::from(42_u8), 42.0);
+    assert_eq!(f128::from(u8::MAX), 255.0);
+    assert_eq!(f128::from(i8::MIN), -128.0);
+    assert_eq!(f128::from(42_i8), 42.0);
+    assert_eq!(f128::from(i8::MAX), 127.0);
+    assert_eq!(f128::from(u16::MIN), 0.0);
+    assert_eq!(f128::from(42_u16), 42.0);
+    assert_eq!(f128::from(u16::MAX), 65535.0);
+    assert_eq!(f128::from(i16::MIN), -32768.0);
+    assert_eq!(f128::from(42_i16), 42.0);
+    assert_eq!(f128::from(i16::MAX), 32767.0);
+    assert_eq!(f128::from(u32::MIN), 0.0);
+    assert_eq!(f128::from(42_u32), 42.0);
+    assert_eq!(f128::from(u32::MAX), 4294967295.0);
+    assert_eq!(f128::from(i32::MIN), -2147483648.0);
+    assert_eq!(f128::from(42_i32), 42.0);
+    assert_eq!(f128::from(i32::MAX), 2147483647.0);
+    // FIXME(f16_f128): Uncomment these tests once the From<{u64,i64}> impls are added.
+    // assert_eq!(f128::from(u64::MIN), 0.0);
+    // assert_eq!(f128::from(42_u64), 42.0);
+    // assert_eq!(f128::from(u64::MAX), 18446744073709551615.0);
+    // assert_eq!(f128::from(i64::MIN), -9223372036854775808.0);
+    // assert_eq!(f128::from(42_i64), 42.0);
+    // assert_eq!(f128::from(i64::MAX), 9223372036854775807.0);
+}
diff --git a/library/std/tests/floats/f16.rs b/library/std/tests/floats/f16.rs
index 19389a9178e..ca0b8efbe83 100644
--- a/library/std/tests/floats/f16.rs
+++ b/library/std/tests/floats/f16.rs
@@ -953,3 +953,15 @@ fn test_total_cmp() {
     assert_eq!(Ordering::Less, (-s_nan()).total_cmp(&f16::INFINITY));
     assert_eq!(Ordering::Less, (-s_nan()).total_cmp(&s_nan()));
 }
+
+#[test]
+fn test_from() {
+    assert_eq!(f16::from(false), 0.0);
+    assert_eq!(f16::from(true), 1.0);
+    assert_eq!(f16::from(u8::MIN), 0.0);
+    assert_eq!(f16::from(42_u8), 42.0);
+    assert_eq!(f16::from(u8::MAX), 255.0);
+    assert_eq!(f16::from(i8::MIN), -128.0);
+    assert_eq!(f16::from(42_i8), 42.0);
+    assert_eq!(f16::from(i8::MAX), 127.0);
+}