Update to use a more efficient power of 2 check. (#274)

src/mem/address_space.h

@@ -175,7 +175,7 @@ namespace snmalloc
     template<bool committed>
     void* reserve(size_t size)
     {
-      SNMALLOC_ASSERT(bits::next_pow2(size) == size);
+      SNMALLOC_ASSERT(bits::is_pow2(size));
       SNMALLOC_ASSERT(size >= sizeof(void*));
 
       if constexpr (pal_supports<AlignedAllocation, PAL>)

src/mem/sizeclass.h

@@ -183,7 +183,7 @@ namespace snmalloc
     // Client responsible for checking alignment is not zero
     SNMALLOC_ASSERT(alignment != 0);
     // Client responsible for checking alignment is a power of two
-    SNMALLOC_ASSERT(bits::next_pow2(alignment) == alignment);
+    SNMALLOC_ASSERT(bits::is_pow2(alignment));
 
     return ((alignment - 1) | (size - 1)) + 1;
   }