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

Author: beetrees

library/core/src/convert/num.rs

@@ -147,22 +147,42 @@ impl_from!(i16 => isize, #[stable(feature = "lossless_iusize_conv", since = "1.2
 // https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-951.pdf
 
 // Note: integers can only be represented with full precision in a float if
-// they fit in the significand, which is 24 bits in f32 and 53 bits in f64.
+// they fit in the significand, which is:
+// * 11 bits in f16
+// * 24 bits in f32
+// * 53 bits in f64
+// * 113 bits in f128
 // Lossy float conversions are not implemented at this time.
+// FIXME(f16_f128): The `f16`/`f128` impls #`[stable]` attributes should be changed to reference
+// `f16`/`f128` when they are stabilised (trait impls have to have a `#[stable]` attribute, but none
+// of the `f16`/`f128` impls can be used on stable as the `f16` and `f128` types are unstable).
 
 // signed integer -> float
+impl_from!(i8 => f16, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i8 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i8 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(i8 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i16 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i16 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(i16 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(i32 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(i32 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+// FIXME(f16_f128): This impl would allow using `f128` on stable before it is stabilised.
+// impl_from!(i64 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 
 // unsigned integer -> float
+impl_from!(u8 => f16, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u8 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u8 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(u8 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(u16 => f16, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u16 => f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u16 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(u16 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 impl_from!(u32 => f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+impl_from!(u32 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
+// FIXME(f16_f128): This impl would allow using `f128` on stable before it is stabilised.
+// impl_from!(u64 => f128, #[stable(feature = "lossless_float_conv", since = "1.6.0")]);
 
 // float -> float
 // FIXME(f16_f128): adding additional `From<{float}>` impls to `f32` breaks inference. See
@@ -198,8 +218,10 @@ macro_rules! impl_float_from_bool {
 }
 
 // boolean -> float
+impl_float_from_bool!(f16);
 impl_float_from_bool!(f32);
 impl_float_from_bool!(f64);
+impl_float_from_bool!(f128);
 
 // no possible bounds violation
 macro_rules! impl_try_from_unbounded {

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);
+}

library/std/tests/floats/f16.rs

@@ -955,3 +955,15 @@ 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);
+}