Split format and format_finite

Author: dtolnay

benches/bench.rs

@@ -18,7 +18,7 @@ macro_rules! benches {
 
                     b.iter(move || {
                         let value = black_box($value);
-                        let formatted = buf.format(value);
+                        let formatted = buf.format_finite(value);
                         black_box(formatted);
                     });
                 }

examples/upstream_benchmark.rs

@@ -56,7 +56,7 @@ macro_rules! benchmark {
 
                 let t1 = std::time::SystemTime::now();
                 for _ in 0..ITERATIONS {
-                    throwaway += ryu::Buffer::new().format(f).len();
+                    throwaway += ryu::Buffer::new().format_finite(f).len();
                 }
                 let duration = t1.elapsed().unwrap();
                 let nanos = duration.as_secs() * 1_000_000_000 + duration.subsec_nanos() as u64;

src/buffer/mod.rs

@@ -5,13 +5,17 @@ use raw;
 #[cfg(feature = "no-panic")]
 use no_panic::no_panic;
 
+const NAN: &'static str = "NaN";
+const INFINITY: &'static str = "inf";
+const NEG_INFINITY: &'static str = "-inf";
+
 /// Safe API for formatting floating point numbers to text.
 ///
 /// ## Example
 ///
 /// ```edition2018
 /// let mut buffer = ryu::Buffer::new();
-/// let printed = buffer.format(1.234);
+/// let printed = buffer.format_finite(1.234);
 /// assert_eq!(printed, "1.234");
 /// ```
 #[derive(Copy, Clone)]
@@ -30,6 +34,26 @@ impl Buffer {
         }
     }
 
+    /// Print a floating point number into this buffer and return a reference to
+    /// its string representation within the buffer.
+    ///
+    /// # Special cases
+    ///
+    /// This function formats NaN as the string "NaN", positive infinity as
+    /// "inf", and negative infinity as "-inf" to match std::fmt.
+    ///
+    /// If your input is known to be finite, you may get better performance by
+    /// calling the `format_finite` method instead of `format` to avoid the
+    /// checks for special cases.
+    #[cfg_attr(feature = "no-panic", no_panic)]
+    pub fn format<F: Float>(&mut self, f: F) -> &str {
+        if f.is_nonfinite() {
+            f.format_nonfinite()
+        } else {
+            self.format_finite(f)
+        }
+    }
+
     /// Print a floating point number into this buffer and return a reference to
     /// its string representation within the buffer.
     ///
@@ -47,7 +71,7 @@ impl Buffer {
     /// [`is_infinite`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_infinite
     #[inline]
     #[cfg_attr(feature = "no-panic", no_panic)]
-    pub fn format<F: Float>(&mut self, f: F) -> &str {
+    pub fn format_finite<F: Float>(&mut self, f: F) -> &str {
         unsafe {
             let n = f.write_to_ryu_buffer(&mut self.bytes[0]);
             debug_assert!(n <= self.bytes.len());
@@ -74,11 +98,35 @@ pub trait Float: Sealed {}
 impl Float for f32 {}
 impl Float for f64 {}
 
-pub trait Sealed {
+pub trait Sealed: Copy {
+    fn is_nonfinite(self) -> bool;
+    fn format_nonfinite(self) -> &'static str;
     unsafe fn write_to_ryu_buffer(self, result: *mut u8) -> usize;
 }
 
 impl Sealed for f32 {
+    #[inline]
+    #[cfg_attr(feature = "no-panic", no_panic)]
+    fn is_nonfinite(self) -> bool {
+        const EXP_MASK: u32 = 0x7f800000;
+        let bits = unsafe { mem::transmute::<f32, u32>(self) };
+        bits & EXP_MASK == EXP_MASK
+    }
+
+    #[cold]
+    fn format_nonfinite(self) -> &'static str {
+        const MANTISSA_MASK: u32 = 0x007fffff;
+        const SIGN_MASK: u32 = 0x80000000;
+        let bits = unsafe { mem::transmute::<f32, u32>(self) };
+        if bits & MANTISSA_MASK != 0 {
+            NAN
+        } else if bits & SIGN_MASK != 0 {
+            NEG_INFINITY
+        } else {
+            INFINITY
+        }
+    }
+
     #[inline]
     #[cfg_attr(feature = "no-panic", no_panic)]
     unsafe fn write_to_ryu_buffer(self, result: *mut u8) -> usize {
@@ -87,6 +135,28 @@ impl Sealed for f32 {
 }
 
 impl Sealed for f64 {
+    #[inline]
+    #[cfg_attr(feature = "no-panic", no_panic)]
+    fn is_nonfinite(self) -> bool {
+        const EXP_MASK: u64 = 0x7ff0000000000000;
+        let bits = unsafe { mem::transmute::<f64, u64>(self) };
+        bits & EXP_MASK == EXP_MASK
+    }
+
+    #[cold]
+    fn format_nonfinite(self) -> &'static str {
+        const MANTISSA_MASK: u64 = 0x000fffffffffffff;
+        const SIGN_MASK: u64 = 0x8000000000000000;
+        let bits = unsafe { mem::transmute::<f64, u64>(self) };
+        if bits & MANTISSA_MASK != 0 {
+            NAN
+        } else if bits & SIGN_MASK != 0 {
+            NEG_INFINITY
+        } else {
+            INFINITY
+        }
+    }
+
     #[inline]
     #[cfg_attr(feature = "no-panic", no_panic)]
     unsafe fn write_to_ryu_buffer(self, result: *mut u8) -> usize {

tests/d2s_test.rs

@@ -54,7 +54,7 @@ fn test_random() {
     let mut buffer = ryu::Buffer::new();
     for _ in 0..1000000 {
         let f: f64 = rand::random();
-        assert_eq!(f, buffer.format(f).parse().unwrap());
+        assert_eq!(f, buffer.format_finite(f).parse().unwrap());
     }
 }
 
@@ -63,7 +63,7 @@ fn test_non_finite() {
     for i in 0u64..1 << 23 {
         let f = f64::from_bits((((1 << 11) - 1) << 52) + (i << 29));
         assert!(!f.is_finite(), "f={}", f);
-        ryu::Buffer::new().format(f);
+        ryu::Buffer::new().format_finite(f);
     }
 }
 
@@ -73,6 +73,9 @@ fn test_basic() {
     check!(-0.0);
     check!(1.0);
     check!(-1.0);
+    assert_eq!(pretty(f64::NAN), "NaN");
+    assert_eq!(pretty(f64::INFINITY), "inf");
+    assert_eq!(pretty(f64::NEG_INFINITY), "-inf");
 }
 
 #[test]

tests/exhaustive.rs

@@ -40,7 +40,7 @@ fn test_exhaustive() {
                 }
                 let n = unsafe { ryu::raw::format32(f, &mut bytes[0]) };
                 assert_eq!(Ok(Ok(f)), str::from_utf8(&bytes[..n]).map(str::parse));
-                assert_eq!(Ok(f), buffer.format(f).parse());
+                assert_eq!(Ok(f), buffer.format_finite(f).parse());
             }
 
             let increment = (max - min + 1) as usize;

tests/f2s_test.rs

@@ -49,7 +49,7 @@ fn test_random() {
     let mut buffer = ryu::Buffer::new();
     for _ in 0..1000000 {
         let f: f32 = rand::random();
-        assert_eq!(f, buffer.format(f).parse().unwrap());
+        assert_eq!(f, buffer.format_finite(f).parse().unwrap());
     }
 }
 
@@ -58,7 +58,7 @@ fn test_non_finite() {
     for i in 0u32..1 << 23 {
         let f = f32::from_bits((((1 << 8) - 1) << 23) + i);
         assert!(!f.is_finite(), "f={}", f);
-        ryu::Buffer::new().format(f);
+        ryu::Buffer::new().format_finite(f);
     }
 }
 
@@ -68,6 +68,9 @@ fn test_basic() {
     check!(-0.0);
     check!(1.0);
     check!(-1.0);
+    assert_eq!(pretty(f32::NAN), "NaN");
+    assert_eq!(pretty(f32::INFINITY), "inf");
+    assert_eq!(pretty(f32::NEG_INFINITY), "-inf");
 }
 
 #[test]