huffman/huffyuv: move lorens huffman table generation code to huffman.c/h

Reviewed-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/huffman.c

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2006 Konstantin Shishkov
+ * Copyright (c) 2007 Loren Merritt
  *
  * This file is part of FFmpeg.
  *
@@ -111,3 +112,60 @@ int ff_huff_build_tree(AVCodecContext *avctx, VLC *vlc, int nb_codes,
     }
     return 0;
 }
+
+typedef struct {
+    uint64_t val;
+    int name;
+} HeapElem;
+
+static void heap_sift(HeapElem *h, int root, int size)
+{
+    while(root*2+1 < size) {
+        int child = root*2+1;
+        if(child < size-1 && h[child].val > h[child+1].val)
+            child++;
+        if(h[root].val > h[child].val) {
+            FFSWAP(HeapElem, h[root], h[child]);
+            root = child;
+        } else
+            break;
+    }
+}
+
+void ff_generate_len_table(uint8_t *dst, const uint64_t *stats){
+    HeapElem h[256];
+    int up[2*256];
+    int len[2*256];
+    int offset, i, next;
+    int size = 256;
+
+    for(offset=1; ; offset<<=1){
+        for(i=0; i<size; i++){
+            h[i].name = i;
+            h[i].val = (stats[i] << 8) + offset;
+        }
+        for(i=size/2-1; i>=0; i--)
+            heap_sift(h, i, size);
+
+        for(next=size; next<size*2-1; next++){
+            // merge the two smallest entries, and put it back in the heap
+            uint64_t min1v = h[0].val;
+            up[h[0].name] = next;
+            h[0].val = INT64_MAX;
+            heap_sift(h, 0, size);
+            up[h[0].name] = next;
+            h[0].name = next;
+            h[0].val += min1v;
+            heap_sift(h, 0, size);
+        }
+
+        len[2*size-2] = 0;
+        for(i=2*size-3; i>=size; i--)
+            len[i] = len[up[i]] + 1;
+        for(i=0; i<size; i++) {
+            dst[i] = len[up[i]] + 1;
+            if(dst[i] >= 32) break;
+        }
+        if(i==size) break;
+    }
+}