altered version of http://codezine.jp/a/article.aspx?aid=443 by okanohara-san with handling of eof optimized

git-svn-id: http://svn.coderepos.org/share/lang/cplusplus/range_coder@7043 d0d07461-0603-4401-acd4-de1884942a52

Author: kazuho

range_coder.hpp

@@ -0,0 +1,137 @@
+#ifndef __RANGE_CODER_HPP__
+#define __RANGE_CODER_HPP__
+
+// original work by Daisuke Okanohara 2006/06/16
+
+struct rc_type_t {
+  enum {
+    TOP = 1U << 24,
+    TOPMASK = TOP - 1,
+  };
+  typedef unsigned int uint;
+  typedef unsigned char byte;
+};
+
+template <class Store> class rc_encoder_t : public rc_type_t {
+public:
+  rc_encoder_t(Store *_store) : store(_store) {
+    L      = 0;
+    R      = 0xFFFFFFFF;
+    buffer = 0;
+    carryN = 0;
+    counter = 0;
+    start  = true;
+  }
+  void encode(const uint low, const uint high, const uint total) {
+    uint r    = R / total;
+    if (high < total) {
+      R = r * (high-low);
+    } else {
+      R -= r * low;
+    }
+    uint newL = L + r*low;
+    if (newL < L) {
+      //overflow occured (newL >= 2^32)
+      //buffer FF FF .. FF -> buffer+1 00 00 .. 00
+      buffer++;
+      for (;carryN > 0; carryN--) {
+	store->push_back(buffer);
+	buffer = 0;
+      }
+    }
+    L = newL;
+    while (R < TOP) {
+      const byte newBuffer = (L >> 24);
+      if (start) {
+	buffer = newBuffer;
+	start  = false;
+      } else if (newBuffer == 0xFF) {
+	carryN++;
+      } else {
+	store->push_back(buffer);
+	for (; carryN != 0; carryN--) {
+	  store->push_back(0xFF);
+	}
+	buffer = newBuffer;
+      }
+      L <<= 8;
+      R <<= 8;
+    }
+    counter++;
+  }
+  void final() {
+    store->push_back(buffer);
+    for (; carryN != 0; carryN--) {
+      store->push_back(0xFF);
+    }
+    uint t = L + R;
+    while (1) {
+      uint t8 = t >> 24, l8 = L >> 24;
+      store->push_back(l8);
+      if (t8 != l8) {
+	break;
+      }
+      t <<= 8;
+      L <<= 8;
+    }
+  }
+private:
+  uint R;
+  uint L;
+  bool start;
+  byte buffer;
+  uint carryN;
+  Store* store;
+  uint counter;
+};
+
+template <class Iterator, unsigned N> class rc_decoder_t : public rc_type_t {
+public:
+  rc_decoder_t(const Iterator& _i, const Iterator _e) : iter(_i), iter_end(_e) {
+    R = 0xFFFFFFFF;
+    D = 0;
+    for (int i = 0; i < 4; i++) {
+      D = (D << 8) | next();
+    }
+  }
+  uint decode(const uint total, const uint* cumFreq) {
+    const uint r = R / total;
+    const uint targetPos = std::min(total-1, D / r);
+    
+    //find target s.t. cumFreq[target] <= targetPos < cumFreq[target+1]
+    uint left  = 0;
+    uint right = N;
+    while(left < right) {
+      uint mid = (left+right)/2;
+      if (cumFreq[mid+1] <= targetPos) left = mid+1;
+      else                             right = mid;
+    }
+    
+    const uint target = left;
+    const uint low  = cumFreq[target];
+    const uint high = cumFreq[target+1];
+    
+    D -= r * low;
+    if (high != total) {
+      R = r * (high-low);
+    } else {
+      R -= r * low;
+    }
+    
+    while (R < TOP) {
+      R <<= 8;
+      D = (D << 8) | next();
+    }
+    
+    return target;
+  }
+  byte next() {
+    return iter != iter_end ? (byte)*iter++ : 0xff;
+  }
+private:
+  uint R;
+  uint D;
+  Iterator iter, iter_end;
+};
+
+#endif