Update lib.rs

Author: ryancinsight

snmalloc-sys/snmalloc

@@ -33,34 +33,31 @@ extern "C" {
     pub fn rust_realloc(ptr: *mut c_void, alignment: size_t, old_size: size_t, new_size: size_t) -> *mut c_void;
 
     /// Allocate `count` items of `size` length each.
-    ///
     /// Returns `null` if `count * size` overflows or on out-of-memory.
-    ///
     /// All items are initialized to zero.
     pub fn sn_calloc(count: usize, size: usize) -> *mut c_void;
 
     /// Allocate `size` bytes.
-    ///
     /// Returns pointer to the allocated memory or null if out of memory.
     /// Returns a unique pointer if called with `size` 0.
     pub fn sn_malloc(size: usize) -> *mut c_void;
 
     /// Re-allocate memory to `newsize` bytes.
-    ///
     /// Return pointer to the allocated memory or null if out of memory. If null
     /// is returned, the pointer `p` is not freed. Otherwise the original
     /// pointer is either freed or returned as the reallocated result (in case
     /// it fits in-place with the new size).
-    ///
-    /// If `p` is null, it behaves as [`mi_malloc`]. If `newsize` is larger than
+    /// If `p` is null, it behaves as [`sn_malloc`]. If `newsize` is larger than
     /// the original `size` allocated for `p`, the bytes after `size` are
     /// uninitialized.
     pub fn sn_realloc(p: *mut c_void, newsize: usize) -> *mut c_void;
 
     /// Free previously allocated memory.
-    ///
     /// The pointer `p` must have been allocated before (or be null).
     pub fn sn_free(p: *mut c_void);
+	
+    /// Return the available bytes in a memory block.
+    pub fn sn_malloc_usable_size(p: *const c_void) -> usize;
 }
 
 #[cfg(test)]
@@ -94,4 +91,14 @@ mod tests {
         unsafe {assert_eq!(*ptr, 127)};
         unsafe { rust_dealloc(ptr as *mut c_void, 8, 16) };
     }
+
+    #[test]
+    fn it_calculates_usable_size() {
+        let ptr = unsafe { sn_malloc(32) } as *mut u8;
+        let usable_size = unsafe { sn_malloc_usable_size(ptr as *mut c_void) };
+        assert!(
+            usable_size >= 32,
+            "usable_size should at least equal to the allocated size"
+        );
+    }
 }