Add a stupid integerization of the AA&N IDCT -- 30% faster or so, mostly

[fjl] / dehuff.h

diff --git a/dehuff.h b/dehuff.h
index 3d3d8c5b049b192bdb772355603c3ec4f92accc6..69fc798ddd1f426186576e971126101734531b94 100644 (file)
--- a/dehuff.h
+++ b/dehuff.h
@@ -6,7 +6,7 @@
 #include <sys/types.h>
 
 #include "bytesource.h"
-#include "input.h"
+#include "bitsource.h"
 
 // About 99% of all Huffman codes are <= 8 bits long (see codelen.txt),
 // and it's what libjpeg uses. Thus, it seems like a reasonable size.
@@ -66,4 +66,22 @@ static inline unsigned read_huffman_symbol(const struct huffman_table* table,
        return code;
 }
 
+// procedure EXTEND (figure F.12)
+
+// Fast lookup table for (1 << (bits - 1)).
+// The table actually helps, since the load can go in parallel with the shift
+// operation below.
+static const int bit_thresholds[16] = {
+       0, 1 << 0, 1 << 2, 1 << 3, 1 << 4, 1 << 5, 1 << 6, 1 << 7, 1 << 8, 1 << 9, 1 << 10, 1 << 11, 1 << 12, 1 << 13, 1 << 14, 1 << 15
+};
+
+static inline unsigned extend(int val, int bits)
+{
+       if (val < bit_thresholds[bits]) {
+               return val + (-1 << bits) + 1;
+       } else {
+               return val;
+       }
+}
+
 #endif /* !defined(_DEHUFF_H) */