Merge GetBits32() impls into one. Put it in fxcrt.

Review-Url: https://codereview.chromium.org/1990153003

3 files changed, 66 insertions, 3 deletions

diff --git a/core/fxcrt/fx_basic_util.cpp b/core/fxcrt/fx_basic_util.cpp
index aa36d56f38..2d3483e9b3 100644
--- a/core/fxcrt/fx_basic_util.cpp
+++ b/core/fxcrt/fx_basic_util.cpp
@@ -7,8 +7,6 @@
 #include "core/fxcrt/include/fx_basic.h"
 #include "core/fxcrt/include/fx_ext.h"
 
-#include <cctype>
-
 #if _FXM_PLATFORM_ != _FXM_PLATFORM_WINDOWS_
 #include <dirent.h>
 #include <sys/types.h>
@@ -16,6 +14,9 @@
 #include <direct.h>
 #endif
 
+#include <algorithm>
+#include <cctype>
+
 CFX_PrivateData::CFX_PrivateData() {}
 
 CFX_PrivateData::~CFX_PrivateData() {
@@ -364,3 +365,33 @@ CFX_Vector_3by1 CFX_Matrix_3by3::TransformVector(const CFX_Vector_3by1& v) {
                          d * v.a + e * v.b + f * v.c,
                          g * v.a + h * v.b + i * v.c);
 }
+
+uint32_t GetBits32(const uint8_t* pData, int bitpos, int nbits) {
+  ASSERT(0 < nbits && nbits <= 32);
+  const uint8_t* dataPtr = &pData[bitpos / 8];
+  int bitShift;
+  int bitMask;
+  int dstShift;
+  int bitCount = bitpos & 0x07;
+  if (nbits < 8 && nbits + bitCount <= 8) {
+    bitShift = 8 - nbits - bitCount;
+    bitMask = (1 << nbits) - 1;
+    dstShift = 0;
+  } else {
+    bitShift = 0;
+    int bitOffset = 8 - bitCount;
+    bitMask = (1 << std::min(bitOffset, nbits)) - 1;
+    dstShift = nbits - bitOffset;
+  }
+  uint32_t result = (uint32_t)(*dataPtr++ >> bitShift & bitMask) << dstShift;
+  while (dstShift >= 8) {
+    dstShift -= 8;
+    result |= *dataPtr++ << dstShift;
+  }
+  if (dstShift > 0) {
+    bitShift = 8 - dstShift;
+    bitMask = (1 << dstShift) - 1;
+    result |= *dataPtr++ >> bitShift & bitMask;
+  }
+  return result;
+}
diff --git a/core/fxcrt/fx_basic_util_unittest.cpp b/core/fxcrt/fx_basic_util_unittest.cpp
new file mode 100644
index 0000000000..3272eab70c
--- /dev/null
+++ b/core/fxcrt/fx_basic_util_unittest.cpp
@@ -0,0 +1,30 @@
+// Copyright 2016 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.
+
+#include "core/fxcrt/include/fx_basic.h"
+#include "testing/fx_string_testhelpers.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+uint32_t ReferenceGetBits32(const uint8_t* pData, int bitpos, int nbits) {
+  int result = 0;
+  for (int i = 0; i < nbits; i++) {
+    if (pData[(bitpos + i) / 8] & (1 << (7 - (bitpos + i) % 8)))
+      result |= 1 << (nbits - i - 1);
+  }
+  return result;
+}
+
+}  // namespace
+
+TEST(fxge, GetBits32) {
+  unsigned char data[] = {0xDE, 0x3F, 0xB1, 0x7C, 0x12, 0x9A, 0x04, 0x56};
+  for (int nbits = 1; nbits <= 32; ++nbits) {
+    for (int bitpos = 0; bitpos < (int)sizeof(data) * 8 - nbits; ++bitpos) {
+      EXPECT_EQ(ReferenceGetBits32(data, bitpos, nbits),
+                GetBits32(data, bitpos, nbits));
+    }
+  }
+}
diff --git a/core/fxcrt/include/fx_basic.h b/core/fxcrt/include/fx_basic.h
index 7fdfbf699d..d3dce8c749 100644
--- a/core/fxcrt/include/fx_basic.h
+++ b/core/fxcrt/include/fx_basic.h
@@ -178,7 +178,7 @@ class CFX_UTF8Encoder {
 
 class CFX_BasicArray {
  protected:
-  CFX_BasicArray(int unit_size);
+  explicit CFX_BasicArray(int unit_size);
   CFX_BasicArray(const CFX_BasicArray&) = delete;
   ~CFX_BasicArray();
 
@@ -972,4 +972,6 @@ class CFX_Matrix_3by3 {
   FX_FLOAT i;
 };
 
+uint32_t GetBits32(const uint8_t* pData, int bitpos, int nbits);
+
 #endif  // CORE_FXCRT_INCLUDE_FX_BASIC_H_