Use sized deallocation when releasing Zippy's scratch buffers.

name                                          old time/op             new time/op             delta
BM_UFlat/0      [html             ]            41.7µs ± 0%             41.7µs ± 0%    ~             (p=0.222 n=5+5)
BM_UFlat/1      [urls             ]             587µs ± 0%              574µs ± 0%  -2.31%          (p=0.008 n=5+5)
BM_UFlat/2      [jpg              ]            7.24µs ± 2%             7.25µs ± 2%    ~             (p=0.690 n=5+5)
BM_UFlat/3      [jpg_200          ]              130ns ± 0%              131ns ± 1%    ~             (p=0.556 n=4+5)
BM_UFlat/4      [pdf              ]            8.21µs ± 0%             8.24µs ± 1%    ~             (p=0.278 n=5+5)
BM_UFlat/5      [html4            ]             219µs ± 0%              220µs ± 0%  +0.45%          (p=0.008 n=5+5)
BM_UFlat/6      [txt1             ]             192µs ± 0%              190µs ± 0%  -0.86%          (p=0.008 n=5+5)
BM_UFlat/7      [txt2             ]             169µs ± 0%              168µs ± 0%  -0.54%          (p=0.008 n=5+5)
BM_UFlat/8      [txt3             ]             509µs ± 0%              505µs ± 0%  -0.66%          (p=0.008 n=5+5)
BM_UFlat/9      [txt4             ]             710µs ± 0%              702µs ± 0%  -1.14%          (p=0.008 n=5+5)
BM_UFlat/10     [pb               ]            38.2µs ± 0%             37.9µs ± 0%  -0.82%          (p=0.008 n=5+5)
BM_UFlat/11     [gaviota          ]             189µs ± 0%              189µs ± 0%    ~             (p=0.746 n=5+5)
BM_UFlat/12     [cp               ]            14.2µs ± 0%             14.2µs ± 1%    ~             (p=0.421 n=5+5)
BM_UFlat/13     [c                ]            7.29µs ± 0%             7.34µs ± 1%  +0.69%          (p=0.016 n=5+5)
BM_UFlat/14     [lsp              ]            2.27µs ± 0%             2.28µs ± 0%  +0.34%          (p=0.008 n=5+5)
BM_UFlat/15     [xls              ]             954µs ± 0%              900µs ± 0%  -5.67%          (p=0.008 n=5+5)
BM_UFlat/16     [xls_200          ]              213ns ± 1%              217ns ± 2%    ~             (p=0.056 n=5+5)
BM_UFlat/17     [bin              ]             276µs ± 0%              274µs ± 0%  -0.94%          (p=0.008 n=5+5)
BM_UFlat/18     [bin_200          ]              101ns ± 1%              101ns ± 1%    ~             (p=0.524 n=5+5)
BM_UFlat/19     [sum              ]            29.3µs ± 0%             27.3µs ± 0%  -6.98%          (p=0.008 n=5+5)
BM_UFlat/20     [man              ]            2.95µs ± 0%             2.95µs ± 0%    ~             (p=0.651 n=5+5)

For microbenchmarks, the overhead of allocating/deallocating should be
small (the relevant metadata for TCMalloc's PageMap will be in cache),
but this helps demonstrate that the refactoring does not adversely
impact performance.

snappy.cc

@@ -942,6 +942,17 @@ bool GetUncompressedLength(Source* source, uint32* result) {
   return decompressor.ReadUncompressedLength(result);
 }
 
+struct Deleter {
+  Deleter() : size_(0) {}
+  explicit Deleter(size_t size) : size_(size) {}
+
+  void operator()(char* ptr) const {
+    std::allocator<char>().deallocate(ptr, size_);
+  }
+
+  size_t size_;
+};
+
 size_t Compress(Source* reader, Sink* writer) {
   size_t written = 0;
   size_t N = reader->Available();
@@ -952,8 +963,8 @@ size_t Compress(Source* reader, Sink* writer) {
   written += (p - ulength);
 
   internal::WorkingMemory wmem;
-  char* scratch = NULL;
+  std::unique_ptr<char, Deleter> scratch;
-  char* scratch_output = NULL;
+  std::unique_ptr<char, Deleter> scratch_output;
 
   while (N > 0) {
     // Get next block to compress (without copying if possible)
@@ -974,20 +985,21 @@ size_t Compress(Source* reader, Sink* writer) {
         // If this is the last iteration, we want to allocate N bytes
         // of space, otherwise the max possible kBlockSize space.
         // num_to_read contains exactly the correct value
-        scratch = new char[num_to_read];
+        scratch = {
+            std::allocator<char>().allocate(num_to_read), Deleter(num_to_read)};
       }
-      memcpy(scratch, fragment, bytes_read);
+      memcpy(scratch.get(), fragment, bytes_read);
       reader->Skip(bytes_read);
 
       while (bytes_read < num_to_read) {
         fragment = reader->Peek(&fragment_size);
         size_t n = std::min<size_t>(fragment_size, num_to_read - bytes_read);
-        memcpy(scratch + bytes_read, fragment, n);
+        memcpy(scratch.get() + bytes_read, fragment, n);
         bytes_read += n;
         reader->Skip(n);
       }
       assert(bytes_read == num_to_read);
-      fragment = scratch;
+      fragment = scratch.get();
       fragment_size = num_to_read;
     }
     assert(fragment_size == num_to_read);
@@ -1002,13 +1014,14 @@ size_t Compress(Source* reader, Sink* writer) {
     // Need a scratch buffer for the output, in case the byte sink doesn't
     // have room for us directly.
     if (scratch_output == NULL) {
-      scratch_output = new char[max_output];
+      scratch_output =
+          {std::allocator<char>().allocate(max_output), Deleter(max_output)};
     } else {
       // Since we encode kBlockSize regions followed by a region
       // which is <= kBlockSize in length, a previously allocated
       // scratch_output[] region is big enough for this iteration.
     }
-    char* dest = writer->GetAppendBuffer(max_output, scratch_output);
+    char* dest = writer->GetAppendBuffer(max_output, scratch_output.get());
     char* end = internal::CompressFragment(fragment, fragment_size,
                                            dest, table, table_size);
     writer->Append(dest, end - dest);
@@ -1020,9 +1033,6 @@ size_t Compress(Source* reader, Sink* writer) {
 
   Report("snappy_compress", written, uncompressed_size);
 
-  delete[] scratch;
-  delete[] scratch_output;
-
   return written;
 }