Fix stacked borrow violation and add miri CI

.travis.yml

@@ -16,3 +16,8 @@ matrix:
       script:
         - cargo build
         - cargo build --features small
+    - rust: nightly
+      name: Miri
+      script:
+        - rustup component add miri || travis_terminate 0
+        - cargo miri test

src/buffer/mod.rs

@@ -85,36 +85,12 @@ impl Buffer {
     #[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.first_byte_pointer_mut());
+            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.first_byte_pointer(), n);
+            let slice = slice::from_raw_parts(self.bytes.as_ptr() as *const u8, n);
             str::from_utf8_unchecked(slice)
         }
     }
-
-    #[inline]
-    #[cfg(maybe_uninit)]
-    fn first_byte_pointer(&self) -> *const u8 {
-        self.bytes[0].as_ptr()
-    }
-
-    #[inline]
-    #[cfg(not(maybe_uninit))]
-    fn first_byte_pointer(&self) -> *const u8 {
-        &self.bytes[0] as *const u8
-    }
-
-    #[inline]
-    #[cfg(maybe_uninit)]
-    fn first_byte_pointer_mut(&mut self) -> *mut u8 {
-        self.bytes[0].as_mut_ptr()
-    }
-
-    #[inline]
-    #[cfg(not(maybe_uninit))]
-    fn first_byte_pointer_mut(&mut self) -> *mut u8 {
-        &mut self.bytes[0] as *mut u8
-    }
 }
 
 impl Default for Buffer {

tests/d2s_test.rs

@@ -51,13 +51,15 @@ fn test_ryu() {
 
 #[test]
 fn test_random() {
+    let n = if cfg!(miri) { 100 } else { 1000000 };
     let mut buffer = ryu::Buffer::new();
-    for _ in 0..1000000 {
+    for _ in 0..n {
         let f: f64 = rand::random();
         assert_eq!(f, buffer.format_finite(f).parse().unwrap());
     }
 }
 
+#[cfg(not(miri))]
 #[test]
 fn test_non_finite() {
     for i in 0u64..1 << 23 {

tests/f2s_test.rs

@@ -46,13 +46,15 @@ fn test_ryu() {
 
 #[test]
 fn test_random() {
+    let n = if cfg!(miri) { 100 } else { 1000000 };
     let mut buffer = ryu::Buffer::new();
-    for _ in 0..1000000 {
+    for _ in 0..n {
         let f: f32 = rand::random();
         assert_eq!(f, buffer.format_finite(f).parse().unwrap());
     }
 }
 
+#[cfg(not(miri))]
 #[test]
 fn test_non_finite() {
     for i in 0u32..1 << 23 {