range coder

Originally committed as revision 3654 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/rangecoder.h

@@ -0,0 +1,129 @@
+/*
+ * Range coder
+ * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ */
+ 
+/**
+ * @file rangecoder.h
+ * Range coder.
+ */
+
+
+#undef NDEBUG
+#include <assert.h>
+
+typedef struct RangeCoder{
+    int low;
+    int range;
+    int outstanding_count;
+    int outstanding_byte;
+    uint8_t zero_state[256];
+    uint8_t  one_state[256];
+    uint8_t *bytestream_start;
+    uint8_t *bytestream;
+    uint8_t *bytestream_end;
+}RangeCoder;
+
+void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size);
+void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size);
+int ff_rac_terminate(RangeCoder *c);
+void ff_build_rac_states(RangeCoder *c, int factor, int max_p);
+
+static inline void renorm_encoder(RangeCoder *c){
+    //FIXME optimize
+    while(c->range < 0x100){
+        if(c->outstanding_byte < 0){
+            c->outstanding_byte= c->low>>8;
+        }else if(c->low <= 0xFF00){
+            *c->bytestream++ = c->outstanding_byte;
+            for(;c->outstanding_count; c->outstanding_count--)
+                *c->bytestream++ = 0xFF;
+            c->outstanding_byte= c->low>>8;
+        }else if(c->low >= 0x10000){
+            *c->bytestream++ = c->outstanding_byte + 1;
+            for(;c->outstanding_count; c->outstanding_count--)
+                *c->bytestream++ = 0x00;
+            c->outstanding_byte= (c->low>>8) & 0xFF;
+        }else{
+            c->outstanding_count++;
+        }
+        
+        c->low = (c->low & 0xFF)<<8;
+        c->range <<= 8;
+    }
+}
+
+static inline void put_rac(RangeCoder *c, uint8_t * const state, int bit){
+    int range1= (c->range * (*state)) >> 8;
+
+    assert(*state);
+    assert(range1 < c->range);
+    assert(range1 > 0);
+    if(!bit){
+        c->range -= range1;
+        *state= c->zero_state[*state];
+    }else{
+        c->low += c->range - range1;
+        c->range = range1;
+        *state= c->one_state[*state];
+    }
+    
+    renorm_encoder(c);
+}
+
+static inline void refill(RangeCoder *c){
+    if(c->range < 0x100){
+        c->range <<= 8;
+        c->low <<= 8;
+        if(c->bytestream < c->bytestream_end)
+            c->low+= c->bytestream[0];
+        c->bytestream++;
+    }
+}
+
+static inline int get_rac(RangeCoder *c, uint8_t * const state){
+    int range1= (c->range * (*state)) >> 8;
+    int one_mask;
+    
+    c->range -= range1;
+#if 1
+    if(c->low < c->range){
+        *state= c->zero_state[*state];
+        refill(c);
+        return 0;
+    }else{
+        c->low -= c->range;
+        *state= c->one_state[*state];
+        c->range = range1;
+        refill(c);
+        return 1;
+    }
+#else
+    one_mask= (c->range - c->low-1)>>31;
+    
+    c->low -= c->range & one_mask;
+    c->range += (range1 - c->range) & one_mask;
+    
+    *state= c->zero_state[(*state) + (256&one_mask)];
+    
+    refill(c);
+
+    return one_mask&1;
+#endif
+}
+