From dc3802b9103f77480e01d28bacabfd735d0e0739 Mon Sep 17 00:00:00 2001
From: Yury Melnichek <melnichek@gmail.com>
Date: Wed, 12 Jan 2011 23:47:54 +0200
Subject: [PATCH] ReadVarInt64() for an array of a given size.

---
 coding/coding_tests/varint_test.cpp | 25 +++++++++++---
 coding/varint.hpp                   | 53 ++++++++++++++++++++++++++---
 2 files changed, 69 insertions(+), 9 deletions(-)

diff --git a/coding/coding_tests/varint_test.cpp b/coding/coding_tests/varint_test.cpp
index 0889688e67..e7687345e7 100644
--- a/coding/coding_tests/varint_test.cpp
+++ b/coding/coding_tests/varint_test.cpp
@@ -100,8 +100,12 @@ UNIT_TEST(VarIntMax)
 UNIT_TEST(ReadVarInt64Array_EmptyArray)
 {
   vector<int64_t> result;
-  ReadVarInt64Array(NULL, NULL, MakeBackInsertFunctor(result));
-  TEST_EQUAL(result, vector<int64_t>(), ());
+  void const * pEnd = ReadVarInt64Array(NULL, (void *)0, MakeBackInsertFunctor(result));
+  TEST_EQUAL(result, vector<int64_t>(), ("UntilBufferEnd"));
+  TEST_EQUAL(reinterpret_cast<uintptr_t>(pEnd), 0, ("UntilBufferEnd"));
+  pEnd = ReadVarInt64Array(NULL, (size_t)0, MakeBackInsertFunctor(result));
+  TEST_EQUAL(result, vector<int64_t>(), ("GivenSize"));
+  TEST_EQUAL(reinterpret_cast<uintptr_t>(pEnd), 0, ("GivenSize"));
 }
 
 UNIT_TEST(ReadVarInt64Array)
@@ -139,10 +143,21 @@ UNIT_TEST(ReadVarInt64Array)
         WriteVarInt(dst, testValues[j]);
     }
 
-    vector<int64_t> result;
     ASSERT_GREATER(data.size(), 0, ());
-    ReadVarInt64Array(&data[0], &data[0] + data.size(), MakeBackInsertFunctor(result));
-    TEST_EQUAL(result, testValues, ());
+    {
+      vector<int64_t> result;
+      void const * pEnd = ReadVarInt64Array(&data[0], &data[0] + data.size(),
+                                            MakeBackInsertFunctor(result));
+      TEST_EQUAL(pEnd, &data[0] + data.size(), ("UntilBufferEnd", data.size()));
+      TEST_EQUAL(result, testValues, ("UntilBufferEnd", data.size()));
+    }
+    {
+      vector<int64_t> result;
+      void const * pEnd = ReadVarInt64Array(&data[0], testValues.size(),
+                                            MakeBackInsertFunctor(result));
+      TEST_EQUAL(pEnd, &data[0] + data.size(), ("GivenSize", data.size()));
+      TEST_EQUAL(result, testValues, ("GivenSize", data.size()));
+    }
   }
 }
 
diff --git a/coding/varint.hpp b/coding/varint.hpp
index d43f699102..afe0c5e28e 100644
--- a/coding/varint.hpp
+++ b/coding/varint.hpp
@@ -188,22 +188,51 @@ template <typename T, typename TSource> T ReadVarInt(TSource & src)
 
 DECLARE_EXCEPTION(ReadVarIntException, RootException);
 
-template <typename F> void ReadVarInt64Array(void const * pBeg, void const * pEnd, F f)
+namespace impl
+{
+
+class ReadVarInt64ArrayUntilBufferEnd
+{
+public:
+  explicit ReadVarInt64ArrayUntilBufferEnd(void const * pEnd) : m_pEnd(pEnd) {}
+  bool Continue(void const * p) const
+  {
+    ASSERT_LESS_OR_EQUAL(reinterpret_cast<uintptr_t>(p), reinterpret_cast<uintptr_t>(m_pEnd), ());
+    return p < m_pEnd;
+  }
+  void NextVarInt() {}
+private:
+  void const * m_pEnd;
+};
+
+class ReadVarInt64ArrayGivenSize
+{
+public:
+  explicit ReadVarInt64ArrayGivenSize(size_t const count) : m_Remaining(count) {}
+  bool Continue(void const *) const { return m_Remaining > 0; }
+  void NextVarInt() { --m_Remaining; }
+private:
+  size_t m_Remaining;
+};
+
+template <typename F, class WhileConditionT>
+void const * ReadVarInt64Array(void const * pBeg, WhileConditionT whileCondition, F f)
 {
   uint8_t const * const pBegChar = static_cast<uint8_t const *>(pBeg);
-  uint8_t const * const pEndChar = static_cast<uint8_t const *>(pEnd);
   uint64_t res64 = 0;
   uint32_t res32 = 0;
   uint32_t count32 = 0;
   uint32_t count64 = 0;
-  for (uint8_t const * p = pBegChar; p < pEndChar; ++p)
+  uint8_t const * p = pBegChar;
+  while (whileCondition.Continue(p))
   {
-    uint8_t const t = *p;
+    uint8_t const t = *p++;
     res32 += (static_cast<uint32_t>(t & 127) << count32);
     count32 += 7;
     if (!(t & 128))
     {
       f(ZigZagDecode((static_cast<uint64_t>(res32) << count64) + res64));
+      whileCondition.NextVarInt();
       res64 = 0;
       res32 = 0;
       count32 = 0;
@@ -220,4 +249,20 @@ template <typename F> void ReadVarInt64Array(void const * pBeg, void const * pEn
   ASSERT(count32 == 0 && res32 == 0 && res64 == 0, (res64, res32, count32));
   if (count32 != 0)
     MYTHROW(ReadVarIntException, ());
+  return p;
 }
+
+}
+
+template <typename F> inline
+void const * ReadVarInt64Array(void const * pBeg, void const * pEnd, F f)
+{
+  return impl::ReadVarInt64Array(pBeg, impl::ReadVarInt64ArrayUntilBufferEnd(pEnd), f);
+}
+
+template <typename F> inline
+void const * ReadVarInt64Array(void const * pBeg, size_t count, F f)
+{
+  return impl::ReadVarInt64Array(pBeg, impl::ReadVarInt64ArrayGivenSize(count), f);
+}
+