Move CFX_BitStream to its own file

This CL moves the CFX_BitStream code out of fx_basic and into
cfx_bitstream.

Bug: pdfium:867
Change-Id: I5b7e6190a7db1fe1d24feb6bd676035a5c73ee92
Reviewed-on: https://pdfium-review.googlesource.com/12350
Commit-Queue: dsinclair <dsinclair@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

1 files changed, 57 insertions, 0 deletions

diff --git a/core/fxcrt/cfx_bitstream.cpp b/core/fxcrt/cfx_bitstream.cpp
new file mode 100644
index 0000000000..7cf6d36adf
--- /dev/null
+++ b/core/fxcrt/cfx_bitstream.cpp
@@ -0,0 +1,57 @@
+// Copyright 2017 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
+
+#include "core/fxcrt/cfx_bitstream.h"
+
+#include <limits>
+
+#include "core/fxcrt/fx_system.h"
+
+CFX_BitStream::CFX_BitStream(const uint8_t* pData, uint32_t dwSize)
+    : m_BitPos(0), m_BitSize(dwSize * 8), m_pData(pData) {
+  ASSERT(dwSize <= std::numeric_limits<uint32_t>::max() / 8);
+}
+
+CFX_BitStream::~CFX_BitStream() {}
+
+void CFX_BitStream::ByteAlign() {
+  m_BitPos = (m_BitPos + 7) & ~7;
+}
+
+uint32_t CFX_BitStream::GetBits(uint32_t nBits) {
+  if (nBits > m_BitSize || m_BitPos + nBits > m_BitSize)
+    return 0;
+
+  const uint8_t* data = m_pData.Get();
+
+  if (nBits == 1) {
+    int bit = (data[m_BitPos / 8] & (1 << (7 - m_BitPos % 8))) ? 1 : 0;
+    m_BitPos++;
+    return bit;
+  }
+
+  uint32_t byte_pos = m_BitPos / 8;
+  uint32_t bit_pos = m_BitPos % 8;
+  uint32_t bit_left = nBits;
+  uint32_t result = 0;
+  if (bit_pos) {
+    if (8 - bit_pos >= bit_left) {
+      result = (data[byte_pos] & (0xff >> bit_pos)) >> (8 - bit_pos - bit_left);
+      m_BitPos += bit_left;
+      return result;
+    }
+    bit_left -= 8 - bit_pos;
+    result = (data[byte_pos++] & ((1 << (8 - bit_pos)) - 1)) << bit_left;
+  }
+  while (bit_left >= 8) {
+    bit_left -= 8;
+    result |= data[byte_pos++] << bit_left;
+  }
+  if (bit_left)
+    result |= data[byte_pos] >> (8 - bit_left);
+  m_BitPos += nBits;
+  return result;
+}