Switch to using half::f16 (#12)

For better compatibility with `arrow-rs`

Author: emilk

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+- BREAKING: Switch to using `half::f16` [#12](https://github.com/rerun-io/re_arrow2/pull/12)
+
+
 ## [v0.17.0](https://github.com/jorgecarleitao/arrow2/tree/v0.17.0) (2023-03-27)
 
 [Full Changelog](https://github.com/jorgecarleitao/arrow2/compare/v0.16.0...v0.17.0)

Cargo.lock

@@ -118,6 +118,8 @@ arrow-schema = { version = ">=52", optional = true }
 arrow-data = { version = ">=52", optional = true }
 arrow-array = { version = ">=52", optional = true }
 
+half = { version = "2.2", features = ["bytemuck"] }
+
 [target.wasm32-unknown-unknown.dependencies]
 getrandom = { version = "0.2", features = ["js"] }
 

Cargo.toml

@@ -13,6 +13,7 @@
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![cfg_attr(feature = "simd", feature(portable_simd))]
 #![cfg_attr(feature = "nightly_build", feature(build_hasher_simple_hash_one))]
+#![allow(deprecated)] // chrono has a bunch of deprecated stuff
 
 #[macro_use]
 pub mod array;

src/lib.rs

@@ -4,6 +4,8 @@ use std::panic::RefUnwindSafe;
 
 use bytemuck::{Pod, Zeroable};
 
+pub use half::f16;
+
 use super::PrimitiveType;
 
 /// Sealed trait implemented by all physical types that can be allocated,
@@ -331,186 +333,27 @@ impl Neg for months_days_ns {
     }
 }
 
-/// Type representation of the Float16 physical type
-#[derive(Copy, Clone, Default, Zeroable, Pod)]
-#[allow(non_camel_case_types)]
-#[repr(C)]
-pub struct f16(pub u16);
-
-impl PartialEq for f16 {
-    #[inline]
-    fn eq(&self, other: &f16) -> bool {
-        if self.is_nan() || other.is_nan() {
-            false
-        } else {
-            (self.0 == other.0) || ((self.0 | other.0) & 0x7FFFu16 == 0)
-        }
-    }
-}
-
-// see https://github.com/starkat99/half-rs/blob/main/src/binary16.rs
-impl f16 {
-    /// The difference between 1.0 and the next largest representable number.
-    pub const EPSILON: f16 = f16(0x1400u16);
-
-    #[inline]
-    #[must_use]
-    pub(crate) const fn is_nan(self) -> bool {
-        self.0 & 0x7FFFu16 > 0x7C00u16
-    }
-
-    /// Casts from u16.
-    #[inline]
-    pub const fn from_bits(bits: u16) -> f16 {
-        f16(bits)
-    }
-
-    /// Casts to u16.
-    #[inline]
-    pub const fn to_bits(self) -> u16 {
-        self.0
-    }
-
-    /// Casts this `f16` to `f32`
-    pub fn to_f32(self) -> f32 {
-        let i = self.0;
-        // Check for signed zero
-        if i & 0x7FFFu16 == 0 {
-            return f32::from_bits((i as u32) << 16);
-        }
-
-        let half_sign = (i & 0x8000u16) as u32;
-        let half_exp = (i & 0x7C00u16) as u32;
-        let half_man = (i & 0x03FFu16) as u32;
-
-        // Check for an infinity or NaN when all exponent bits set
-        if half_exp == 0x7C00u32 {
-            // Check for signed infinity if mantissa is zero
-            if half_man == 0 {
-                let number = (half_sign << 16) | 0x7F80_0000u32;
-                return f32::from_bits(number);
-            } else {
-                // NaN, keep current mantissa but also set most significiant mantissa bit
-                let number = (half_sign << 16) | 0x7FC0_0000u32 | (half_man << 13);
-                return f32::from_bits(number);
-            }
-        }
-
-        // Calculate single-precision components with adjusted exponent
-        let sign = half_sign << 16;
-        // Unbias exponent
-        let unbiased_exp = ((half_exp as i32) >> 10) - 15;
-
-        // Check for subnormals, which will be normalized by adjusting exponent
-        if half_exp == 0 {
-            // Calculate how much to adjust the exponent by
-            let e = (half_man as u16).leading_zeros() - 6;
-
-            // Rebias and adjust exponent
-            let exp = (127 - 15 - e) << 23;
-            let man = (half_man << (14 + e)) & 0x7F_FF_FFu32;
-            return f32::from_bits(sign | exp | man);
-        }
-
-        // Rebias exponent for a normalized normal
-        let exp = ((unbiased_exp + 127) as u32) << 23;
-        let man = (half_man & 0x03FFu32) << 13;
-        f32::from_bits(sign | exp | man)
-    }
-
-    /// Casts an `f32` into `f16`
-    pub fn from_f32(value: f32) -> Self {
-        let x: u32 = value.to_bits();
-
-        // Extract IEEE754 components
-        let sign = x & 0x8000_0000u32;
-        let exp = x & 0x7F80_0000u32;
-        let man = x & 0x007F_FFFFu32;
-
-        // Check for all exponent bits being set, which is Infinity or NaN
-        if exp == 0x7F80_0000u32 {
-            // Set mantissa MSB for NaN (and also keep shifted mantissa bits)
-            let nan_bit = if man == 0 { 0 } else { 0x0200u32 };
-            return f16(((sign >> 16) | 0x7C00u32 | nan_bit | (man >> 13)) as u16);
-        }
-
-        // The number is normalized, start assembling half precision version
-        let half_sign = sign >> 16;
-        // Unbias the exponent, then bias for half precision
-        let unbiased_exp = ((exp >> 23) as i32) - 127;
-        let half_exp = unbiased_exp + 15;
-
-        // Check for exponent overflow, return +infinity
-        if half_exp >= 0x1F {
-            return f16((half_sign | 0x7C00u32) as u16);
-        }
-
-        // Check for underflow
-        if half_exp <= 0 {
-            // Check mantissa for what we can do
-            if 14 - half_exp > 24 {
-                // No rounding possibility, so this is a full underflow, return signed zero
-                return f16(half_sign as u16);
-            }
-            // Don't forget about hidden leading mantissa bit when assembling mantissa
-            let man = man | 0x0080_0000u32;
-            let mut half_man = man >> (14 - half_exp);
-            // Check for rounding (see comment above functions)
-            let round_bit = 1 << (13 - half_exp);
-            if (man & round_bit) != 0 && (man & (3 * round_bit - 1)) != 0 {
-                half_man += 1;
-            }
-            // No exponent for subnormals
-            return f16((half_sign | half_man) as u16);
-        }
-
-        // Rebias the exponent
-        let half_exp = (half_exp as u32) << 10;
-        let half_man = man >> 13;
-        // Check for rounding (see comment above functions)
-        let round_bit = 0x0000_1000u32;
-        if (man & round_bit) != 0 && (man & (3 * round_bit - 1)) != 0 {
-            // Round it
-            f16(((half_sign | half_exp | half_man) + 1) as u16)
-        } else {
-            f16((half_sign | half_exp | half_man) as u16)
-        }
-    }
-}
-
-impl std::fmt::Debug for f16 {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{:?}", self.to_f32())
-    }
-}
-
-impl std::fmt::Display for f16 {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.to_f32())
-    }
-}
-
 impl NativeType for f16 {
     const PRIMITIVE: PrimitiveType = PrimitiveType::Float16;
     type Bytes = [u8; 2];
     #[inline]
     fn to_le_bytes(&self) -> Self::Bytes {
-        self.0.to_le_bytes()
+        f16::to_le_bytes(*self)
     }
 
     #[inline]
     fn to_be_bytes(&self) -> Self::Bytes {
-        self.0.to_be_bytes()
+        f16::to_be_bytes(*self)
     }
 
     #[inline]
     fn from_be_bytes(bytes: Self::Bytes) -> Self {
-        Self(u16::from_be_bytes(bytes))
+        f16::from_be_bytes(bytes)
     }
 
     #[inline]
     fn from_le_bytes(bytes: Self::Bytes) -> Self {
-        Self(u16::from_le_bytes(bytes))
+        f16::from_le_bytes(bytes)
     }
 }
 
@@ -627,11 +470,14 @@ mod test {
         // diff must be <= 4 * EPSILON, as 7 has two more significant bits than 1
         assert!(diff <= 4.0 * f16::EPSILON.to_f32());
 
-        assert_eq!(f16(0x0000_0001).to_f32(), 2.0f32.powi(-24));
-        assert_eq!(f16(0x0000_0005).to_f32(), 5.0 * 2.0f32.powi(-24));
+        assert_eq!(f16::from_bits(0x0000_0001).to_f32(), 2.0f32.powi(-24));
+        assert_eq!(f16::from_bits(0x0000_0005).to_f32(), 5.0 * 2.0f32.powi(-24));
 
-        assert_eq!(f16(0x0000_0001), f16::from_f32(2.0f32.powi(-24)));
-        assert_eq!(f16(0x0000_0005), f16::from_f32(5.0 * 2.0f32.powi(-24)));
+        assert_eq!(f16::from_bits(0x0000_0001), f16::from_f32(2.0f32.powi(-24)));
+        assert_eq!(
+            f16::from_bits(0x0000_0005),
+            f16::from_f32(5.0 * 2.0f32.powi(-24))
+        );
 
         assert_eq!(format!("{}", f16::from_f32(7.0)), "7".to_string());
         assert_eq!(format!("{:?}", f16::from_f32(7.0)), "7.0".to_string());