1 files changed, 180 insertions, 0 deletions
diff --git a/src/buffer/mod.rs b/src/buffer/mod.rs
new file mode 100644
index 0000000..df21fe0
--- /dev/null
+++ b/src/buffer/mod.rs
@@ -0,0 +1,180 @@
+use crate::raw;
+#[cfg(maybe_uninit)]
+use core::mem::MaybeUninit;
+use core::{mem, slice, str};
+#[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
+///
+/// ```
+/// let mut buffer = ryu::Buffer::new();
+/// let printed = buffer.format_finite(1.234);
+/// assert_eq!(printed, "1.234");
+/// ```
+pub struct Buffer {
+    #[cfg(maybe_uninit)]
+    bytes: [MaybeUninit<u8>; 24],
+    #[cfg(not(maybe_uninit))]
+    bytes: [u8; 24],
+}
+
+impl Buffer {
+    /// This is a cheap operation; you don't need to worry about reusing buffers
+    /// for efficiency.
+    #[inline]
+    #[cfg_attr(feature = "no-panic", no_panic)]
+    pub fn new() -> Self {
+        // assume_init is safe here, since this is an array of MaybeUninit, which does not need
+        // to be initialized.
+        #[cfg(maybe_uninit)]
+        let bytes = [MaybeUninit::<u8>::uninit(); 24];
+        #[cfg(not(maybe_uninit))]
+        let bytes = unsafe { mem::uninitialized() };
+
+        Buffer { bytes: bytes }
+    }
+
+    /// 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", inline)]
+    #[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.
+    ///
+    /// # Special cases
+    ///
+    /// This function **does not** check for NaN or infinity. If the input
+    /// number is not a finite float, the printed representation will be some
+    /// correctly formatted but unspecified numerical value.
+    ///
+    /// Please check [`is_finite`] yourself before calling this function, or
+    /// check [`is_nan`] and [`is_infinite`] and handle those cases yourself.
+    ///
+    /// [`is_finite`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_finite
+    /// [`is_nan`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_nan
+    /// [`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_finite<F: Float>(&mut self, f: F) -> &str {
+        unsafe {
+            let n = f.write_to_ryu_buffer(self.bytes.as_mut_ptr() as *mut u8);
+            debug_assert!(n <= self.bytes.len());
+            let slice = slice::from_raw_parts(self.bytes.as_ptr() as *const u8, n);
+            str::from_utf8_unchecked(slice)
+        }
+    }
+}
+
+impl Copy for Buffer {}
+
+impl Clone for Buffer {
+    #[inline]
+    fn clone(&self) -> Self {
+        Buffer::new()
+    }
+}
+
+impl Default for Buffer {
+    #[inline]
+    #[cfg_attr(feature = "no-panic", no_panic)]
+    fn default() -> Self {
+        Buffer::new()
+    }
+}
+
+/// A floating point number, f32 or f64, that can be written into a
+/// [`ryu::Buffer`][Buffer].
+///
+/// This trait is sealed and cannot be implemented for types outside of the
+/// `ryu` crate.
+pub trait Float: Sealed {}
+impl Float for f32 {}
+impl Float for f64 {}
+
+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]
+    fn is_nonfinite(self) -> bool {
+        const EXP_MASK: u32 = 0x7f800000;
+        let bits = unsafe { mem::transmute::<f32, u32>(self) };
+        bits & EXP_MASK == EXP_MASK
+    }
+
+    #[cold]
+    #[cfg_attr(feature = "no-panic", inline)]
+    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]
+    unsafe fn write_to_ryu_buffer(self, result: *mut u8) -> usize {
+        raw::format32(self, result)
+    }
+}
+
+impl Sealed for f64 {
+    #[inline]
+    fn is_nonfinite(self) -> bool {
+        const EXP_MASK: u64 = 0x7ff0000000000000;
+        let bits = unsafe { mem::transmute::<f64, u64>(self) };
+        bits & EXP_MASK == EXP_MASK
+    }
+
+    #[cold]
+    #[cfg_attr(feature = "no-panic", inline)]
+    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]
+    unsafe fn write_to_ryu_buffer(self, result: *mut u8) -> usize {
+        raw::format64(self, result)
+    }
+}