calc functions and zxq5 logo in fetch

- changed the crystalfetch text
- added functions to the calculator

src/user/bin/calc/functions.rs

@@ -0,0 +1,27 @@
+use alloc::format;
+use alloc::string::String;
+use crate::println;
+
+pub fn run_func(func: String, x: f64) -> Result<f64, String> {
+    println!("function being run: {}({})", func, x);
+
+    match func.as_str() {
+        "sqrt" => sqrt(x),
+        "ln" => ln(x),
+        _ => Err(String::from(format!("unrecognised function name: {}", func))),
+    }
+}
+
+fn sqrt(x: f64) -> Result<f64, String> {
+    if x < 0.0 {
+        return Err(String::from("Cannot take the square root of a negative number"));
+    }
+    Ok(libm::sqrt(x))
+}
+
+fn ln(x: f64) -> Result<f64, String> {
+    if x < 0.0 {
+        return Err(String::from("Cannot take the natural log of a negative number"));
+    }
+    Ok(libm::log(x))
+}