Fix exp function to actually work

It was calling into decNumberExp with the wrong signature, so it didn't work at all.

I also fixed the decNumber tests for exp so that they'll actually ru if point at the exp.decTest file, and I added a super basic test for ln and exp.

It seems a bit too easy to not run some tests by accident right now; maybe it would be good to expect every test file to have some non-igored tests, and then just delete the test files for actually unimplemented functionality?

decTest/exp.decTest

@@ -540,6 +540,7 @@ expx1200 exp 1 -> 2.718281828459045235360287471352662 Inexact Rounded
 Precision: 34
 maxExponent: 6144
 minExponent: -6143
+clamp: 1
 expx1201 exp 309.5948855821510212996700645087188  -> 2.853319692901387521201738015050724E+134 Inexact Rounded
 expx1202 exp 9.936543068706211420422803962680164  -> 20672.15839203171877476511093276022 Inexact Rounded
 expx1203 exp 6.307870323881505684429839491707908  -> 548.8747777054637296137277391754665 Inexact Rounded

src/bin/run-test.rs

@@ -494,6 +494,7 @@ fn run_test<'a>(env: &Environment, test: Test<'a>) -> TestResult<'a> {
                                   &test);
         }
         Op::Divide(a, b) => simple_op!(test, value = div(a, b)),
+        Op::Exp(a) => simple_op!(test, value = exp(a)),
         Op::Fma(a, b, c) => simple_op!(test, value = mul_add(a, b, c)),
         Op::Invert(a) => simple_op!(test, value = not(a)),
         Op::LogB(a) => simple_op!(test, value = logb(a)),

src/dec128.rs

@@ -617,13 +617,11 @@ impl d128 {
     /// respectively). Inexact results will almost always be correctly rounded, but may be up to 1
     /// ulp (unit in last place) in error in rare cases. This is a mathematical function; the
     /// 10<sup>6</sup> restrictions on precision and range apply as described above.
-    pub fn exp<O: AsRef<d128>>(mut self, exp: O) -> d128 {
+    pub fn exp(mut self) -> d128 {
         d128::with_context(|ctx| unsafe {
             let mut num_self: decNumber = uninitialized();
-            let mut num_exp: decNumber = uninitialized();
             decimal128ToNumber(&self, &mut num_self);
-            decimal128ToNumber(exp.as_ref(), &mut num_exp);
-            decNumberExp(&mut num_self, &num_self, &num_exp, ctx);
+            decNumberExp(&mut num_self, &num_self, ctx);
             *decimal128FromNumber(&mut self, &num_self, ctx)
         })
     }
@@ -948,7 +946,6 @@ extern "C" {
                       ctx: *mut Context)
                       -> *mut decNumber;
     fn decNumberExp(res: *mut decNumber,
-                    lhs: *const decNumber,
                     rhs: *const decNumber,
                     ctx: *mut Context)
                     -> *mut decNumber;
@@ -1093,4 +1090,9 @@ mod tests {
         assert_eq!(d128::from_str(&(::std::u64::MIN).to_string()).unwrap(),
                    d128::from(::std::u64::MIN));
     }
+
+    #[test]
+    fn math_op() {
+        assert_eq!(d128!(1), d128!(1).ln().exp());
+    }
 }