Expand README

README.md

@@ -1,3 +1,31 @@
 # 80-bit Extended-Precision Floating-Point Numbers
 
 This is a Go library that provides a type for representing 80-bit extended-precision floating-point numbers. It is licensed under the terms of the MIT license, see [LICENSE.txt](LICENSE.txt) for details.
+
+## Example
+
+```
+package main
+
+import (
+    "fmt"
+    "github.com/depp/extended"
+)
+
+func main() {
+    e := extended.Extended{
+        SignExponent: 0x3fff,
+        Fraction:     0xC000000000000000,
+    }
+    // Prints "Value: 1.5"
+    fmt.Println("Value:", e.Float64())
+}
+```
+
+## Rounding, Infinity, and NaN
+
+This library uses round-to-even when converting from 80-bit floats to 64-bit floats. This should be what you’re used to, and what you expect! In round-to-even, when an 80-bit float is exactly half-way between two possible `float64` values, the value with a zero in the least-significant bit is chosen (or the value with the larger exponent is chosen, if the values have different exponents).
+
+Values which are outside the range of possible `float64` values are rounded to infinity.
+
+Infinity and NaN are preserved. Different types of NaN values are not distinguished from each other, but the sign of NaN values is preserved during conversion.