Refactor use of sizeclasses (#415)

The primary aim for this refactor is to use a representation for
sizeclasses that uniformly covers both large and small.  This allows
certain operations such as alloc_size and external_pointer to be
uniformly implemented.

The additional types make clear which kind of sizeclass is in use.

This also tidies up the code for sizeclass based divisible by and
modulus.

It fixes a bug in rust_realloc that didn't correctly determine a realloc
was required for large classes.

src/test/func/memory/memory.cc

@@ -236,11 +236,18 @@ void test_external_pointer()
   // Malloc does not have an external pointer querying mechanism.
   auto& alloc = ThreadAlloc::get();
 
-  for (uint8_t sc = 0; sc < NUM_SIZECLASSES; sc++)
+  for (uint8_t sc = 0; sc < NUM_SMALL_SIZECLASSES; sc++)
   {
     size_t size = sizeclass_to_size(sc);
     void* p1 = alloc.alloc(size);
 
+    if (size != alloc.alloc_size(p1))
+    {
+      std::cout << "Requested size: " << size
+                << " alloc_size: " << alloc.alloc_size(p1) << std::endl;
+      abort();
+    }
+
     for (size_t offset = 0; offset < size; offset += 17)
     {
       void* p2 = pointer_offset(p1, offset);
@@ -248,8 +255,9 @@ void test_external_pointer()
       void* p4 = alloc.external_pointer<End>(p2);
       if (p1 != p3)
       {
-        std::cout << "size: " << size << " offset: " << offset << " p1: " << p1
-                  << "  p3: " << p3 << std::endl;
+        std::cout << "size: " << size << " alloc_size: " << alloc.alloc_size(p1)
+                  << " offset: " << offset << " p1: " << p1 << "  p3: " << p3
+                  << std::endl;
       }
       SNMALLOC_CHECK(p1 == p3);
       if ((size_t)p4 != (size_t)p1 + size - 1)
@@ -272,7 +280,11 @@ void check_offset(void* base, void* interior)
   auto& alloc = ThreadAlloc::get();
   void* calced_base = alloc.external_pointer((void*)interior);
   if (calced_base != (void*)base)
+  {
+    std::cout << "Calced base: " << calced_base << " actual base: " << base
+              << " for interior: " << interior << std::endl;
     abort();
+  }
 }
 
 void check_external_pointer_large(size_t* base)
@@ -301,7 +313,7 @@ void test_external_pointer_large()
 
   for (size_t i = 0; i < count; i++)
   {
-    size_t b = MAX_SIZECLASS_BITS + 3;
+    size_t b = MAX_SMALL_SIZECLASS_BITS + 3;
     size_t rand = r.next() & ((1 << b) - 1);
     size_t size = (1 << 24) + rand;
     total_size += size;
@@ -383,7 +395,7 @@ void test_calloc_large_bug()
   // Some PALS have special paths for PAGE aligned zeroing of large
   // allocations.  This is a large allocation that is intentionally
   // not a multiple of page size.
-  const size_t size = (MAX_SIZECLASS_SIZE << 3) - 7;
+  const size_t size = (MAX_SMALL_SIZECLASS_SIZE << 3) - 7;
 
   void* p1 = alloc.alloc<YesZero>(size);
   SNMALLOC_CHECK(alloc.alloc_size(alloc.external_pointer(p1)) >= size);
@@ -415,7 +427,7 @@ void test_static_sized_allocs()
 {
   // For each small, medium, and large class, do each kind dealloc.  This is
   // mostly to ensure that all of these forms compile.
-  for (size_t sc = 0; sc < NUM_SIZECLASSES; sc++)
+  for (size_t sc = 0; sc < NUM_SMALL_SIZECLASSES; sc++)
   {
     // test_static_sized_alloc<sc, 0>();
     // test_static_sized_alloc<sc, 1>();
@@ -430,6 +442,32 @@ void test_static_sized_allocs()
   // test_static_sized_alloc<large_sizeclass_to_size(0), 2>();
 }
 
+void test_remaining_bytes()
+{
+  auto& alloc = ThreadAlloc::get();
+  for (size_t sc = 0; sc < NUM_SMALL_SIZECLASSES; sc++)
+  {
+    auto size = sizeclass_to_size(sc);
+    char* p = (char*)alloc.alloc(size);
+    for (size_t offset = 0; offset < size; offset++)
+    {
+      auto rem = alloc.remaining_bytes(p + offset);
+      if (rem != (size - offset))
+      {
+        printf(
+          "Allocation size: %zu,  Offset: %zu,  Remaining bytes: %zu, "
+          "Expected: %zu\n",
+          size,
+          offset,
+          rem,
+          size - offset);
+        abort();
+      }
+    }
+    alloc.dealloc(p);
+  }
+}
+
 int main(int argc, char** argv)
 {
   setup();
@@ -455,12 +493,12 @@ int main(int argc, char** argv)
   UNUSED(argc);
   UNUSED(argv);
 #endif
-
   test_alloc_dealloc_64k();
   test_random_allocation();
   test_calloc();
   test_double_alloc();
 #ifndef SNMALLOC_PASS_THROUGH // Depends on snmalloc specific features
+  test_remaining_bytes();
   test_static_sized_allocs();
   test_calloc_large_bug();
   test_external_pointer_dealloc_bug();