Move fx_extension implementation to cpp file

This CL moves the GetBits32 implemenation into fx_extension.cpp. It
also moves some of the fx_basic unittests to the correct unittest files.

Change-Id: I2cf8657c228375508db0f02baa628d62a3b2ab25
Reviewed-on: https://pdfium-review.googlesource.com/12673
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/core/fxcrt/fx_extension.cpp b/core/fxcrt/fx_extension.cpp
index 10b568ec9e..2d485490ca 100644
--- a/core/fxcrt/fx_extension.cpp
+++ b/core/fxcrt/fx_extension.cpp
@@ -6,6 +6,7 @@
 
 #include "core/fxcrt/fx_extension.h"
 
+#include <algorithm>
 #include <cwctype>
 
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
@@ -271,3 +272,34 @@ CFX_ByteString FX_GUID_ToString(const FX_GUID* pGUID, bool bSeparator) {
   return bsStr;
 }
 #endif  // PDF_ENABLE_XFA
+
+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 =
+      static_cast<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;
+}