improve profiled performance of C++ BitArray::get(). Closes issue 1101

From evansepdx. Thanks!

git-svn-id: https://zxing.googlecode.com/svn/trunk@2083 59b500cc-1b3d-0410-9834-0bbf25fbcc57

cpp/core/src/zxing/common/BitArray.cpp

@@ -1,8 +1,5 @@
 // -*- mode:c++; tab-width:2; indent-tabs-mode:nil; c-basic-offset:2 -*-
 /*
- *  BitArray.cpp
- *  zxing
- *
  *  Copyright 2010 ZXing authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -19,32 +16,14 @@
  */
 
 #include <zxing/common/BitArray.h>
-#include <iostream>
-#include <limits>
 
 using namespace std;
 
 namespace zxing {
 
-static unsigned int logDigits(unsigned digits) {
-  unsigned log = 0;
-  unsigned val = 1;
-  while (val < digits) {
-    log++;
-    val <<= 1;
-  }
-  return log;
-}
-
-const unsigned int BitArray::bitsPerWord_ = numeric_limits<unsigned int>::digits;
-const unsigned int BitArray::logBits_ = logDigits(bitsPerWord_);
-const unsigned int BitArray::bitsMask_ = (1 << logBits_) - 1;
 
 size_t BitArray::wordsForBits(size_t bits) {
-  int arraySize = bits >> logBits_;
+  int arraySize = (bits + bitsPerWord_ - 1) >> logBits_;
-  if (bits - (arraySize << logBits_) != 0) {
-    arraySize++;
-  }
   return arraySize;
 }
 

cpp/core/src/zxing/common/BitArray.h

@@ -3,9 +3,6 @@
 #define __BIT_ARRAY_H__
 
 /*
- *  BitArray.h
- *  zxing
- *
  *  Copyright 2010 ZXing authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -24,17 +21,26 @@
 #include <zxing/common/Counted.h>
 #include <zxing/common/IllegalArgumentException.h>
 #include <vector>
-#include <iostream>
+#include <limits>
 
 namespace zxing {
 
+#define ZX_LOG_DIGITS(digits) \
+    ((digits == 8) ? 3 : \
+     ((digits == 16) ? 4 : \
+      ((digits == 32) ? 5 : \
+       ((digits == 64) ? 6 : \
+        ((digits == 128) ? 7 : \
+         (-1))))))
+
 class BitArray : public Counted {
 private:
   size_t size_;
   std::vector<unsigned int> bits_;
-  static const unsigned int bitsPerWord_;
+  static const unsigned int bitsPerWord_ =
-  static const unsigned int logBits_;
+    std::numeric_limits<unsigned int>::digits;
-  static const unsigned int bitsMask_;
+  static const unsigned int logBits_ = ZX_LOG_DIGITS(bitsPerWord_);
+  static const unsigned int bitsMask_ = (1 << logBits_) - 1;
   static size_t wordsForBits(size_t bits);
   explicit BitArray();
 

cpp/core/src/zxing/common/BitMatrix.cpp

@@ -1,8 +1,5 @@
 // -*- mode:c++; tab-width:2; indent-tabs-mode:nil; c-basic-offset:2 -*-
 /*
- *  BitMatrix.cpp
- *  zxing
- *
  *  Copyright 2010 ZXing authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -35,26 +32,24 @@ using zxing::Ref;
 namespace {
   size_t wordsForSize(size_t width,
                       size_t height,
+                      unsigned int bitsPerWord,
                       unsigned int logBits) {
     size_t bits = width * height;
-    int arraySize = bits >> logBits;
+    int arraySize = (bits + bitsPerWord - 1) >> logBits;
-    if (bits - (arraySize << logBits) != 0) {
-      arraySize++;
-    }
     return arraySize;
   }
 }
 
 BitMatrix::BitMatrix(size_t dimension) :
   width_(dimension), height_(dimension), words_(0), bits_(NULL) {
-  words_ = wordsForSize(width_, height_, logBits);
+  words_ = wordsForSize(width_, height_, bitsPerWord, logBits);
   bits_ = new unsigned int[words_];
   clear();
 }
 
 BitMatrix::BitMatrix(size_t width, size_t height) :
   width_(width), height_(height), words_(0), bits_(NULL) {
-  words_ = wordsForSize(width_, height_, logBits);
+  words_ = wordsForSize(width_, height_, bitsPerWord, logBits);
   bits_ = new unsigned int[words_];
   clear();
 }