Add Rhai book.

doc/src/language/num-fn.md

@@ -0,0 +1,32 @@
+Numeric Functions
+================
+
+{{#include ../links.md}}
+
+Integer Functions
+----------------
+
+The following standard functions (defined in the [`BasicMathPackage`](/rust/packages.md) but excluded if using a [raw `Engine`])
+operate on `i8`, `i16`, `i32`, `i64`, `f32` and `f64` only:
+
+| Function     | Description                       |
+| ------------ | --------------------------------- |
+| `abs`        | absolute value                    |
+| [`to_float`] | converts an integer type to `f64` |
+
+Floating-Point Functions
+-----------------------
+
+The following standard functions (defined in the [`BasicMathPackage`](/rust/packages.md) but excluded if using a [raw `Engine`])
+operate on `f64` only:
+
+| Category         | Functions                                                             |
+| ---------------- | --------------------------------------------------------------------- |
+| Trigonometry     | `sin`, `cos`, `tan`, `sinh`, `cosh`, `tanh` in degrees                |
+| Arc-trigonometry | `asin`, `acos`, `atan`, `asinh`, `acosh`, `atanh` in degrees          |
+| Square root      | `sqrt`                                                                |
+| Exponential      | `exp` (base _e_)                                                      |
+| Logarithmic      | `ln` (base _e_), `log10` (base 10), `log` (any base)                  |
+| Rounding         | `floor`, `ceiling`, `round`, `int`, `fraction` methods and properties |
+| Conversion       | [`to_int`]                                                            |
+| Testing          | `is_nan`, `is_finite`, `is_infinite` methods and properties           |