Fix a Makefile typo.

[fjl] / dehuff.h

diff --git a/dehuff.h b/dehuff.h
index 224005f84ad3dcb2797c9086a11485c8269c825c..0f86c3b9c4f4e6703e13751dbb9d5306267ed264 100644 (file)
--- a/dehuff.h
+++ b/dehuff.h
@@ -14,6 +14,15 @@
 #define DEHUF_TABLE_SIZE (1 << DEHUF_TABLE_BITS)
 static const int DEHUF_SLOW_PATH = -1;
 
+// About 98% of all AC coefficients (control byte + coefficient) are <= 10 bits
+// long; again, see codelen.txt. This will cost us about 6 kB of data to store
+// in L1 cache.
+#define DEHUF_AC_TABLE_BITS 10
+#define DEHUF_AC_TABLE_SIZE (1 << DEHUF_AC_TABLE_BITS)
+static const int AC_DEHUF_SLOW_PATH = 0xf0000000;
+static const int AC_END_OF_BLOCK = 0xf0000001;
+static const int AC_SIXTEEN_ZEROS = 0xf0000002;
+
 struct huffman_table {
        unsigned num_codes[17];     // BITS
        unsigned char codes[256];   // HUFFVAL
@@ -33,6 +42,15 @@ struct huffman_table {
        // the lookup tables is int to avoid extra zero extending. 
        int lookup_table_codes[DEHUF_TABLE_SIZE]; 
        int lookup_table_length[DEHUF_TABLE_SIZE]; 
+       
+       // Further lookup tables for decoding AC coefficients.
+       // (Generated but obviously not used for DC coefficients.)
+       // Maps from 10-bit lookahead values to the signed coeffient (_codes),
+       // number of bits to skip (_length) and the number of zero coefficients
+       // after this one (_skip).
+       int ac_table_codes[DEHUF_AC_TABLE_SIZE]; 
+       uint8_t ac_table_length[DEHUF_AC_TABLE_SIZE]; 
+       uint8_t ac_table_skip[DEHUF_AC_TABLE_SIZE]; 
 };
 
 enum coefficient_class {
@@ -48,12 +66,11 @@ void read_huffman_tables(huffman_tables_t* dst, input_func_t* input_func, void*
 unsigned read_huffman_symbol_slow_path(const struct huffman_table* table,
                                        struct bit_source* source);
 
-static inline unsigned read_huffman_symbol(const struct huffman_table* table,
-                                           struct bit_source* source)
+static inline unsigned read_huffman_symbol_no_refill(
+       const struct huffman_table* table,
+       struct bit_source* source)
 {
-       // FIXME: We can read past the end of the stream here in some edge
-       // cases. We need to define some guarantees in the layers above.
-       possibly_refill(source, DEHUF_TABLE_BITS);
+       assert(source->bits_available >= DEHUF_TABLE_BITS);
        unsigned lookup = peek_bits(source, DEHUF_TABLE_BITS);
        int code = table->lookup_table_codes[lookup];
        int length = table->lookup_table_length[lookup];
@@ -61,11 +78,18 @@ static inline unsigned read_huffman_symbol(const struct huffman_table* table,
        if (code == DEHUF_SLOW_PATH) {
                return read_huffman_symbol_slow_path(table, source);
        }
-
+               
        read_bits(source, length);
        return code;
 }
 
+static inline unsigned read_huffman_symbol(const struct huffman_table* table,
+                                           struct bit_source* source)
+{
+       possibly_refill(source, DEHUF_TABLE_BITS);
+       return read_huffman_symbol_no_refill(table, source);
+}
+
 // procedure EXTEND (figure F.12)
 
 // Fast lookup table for (1 << (bits - 1)).
@@ -75,13 +99,24 @@ static const int bit_thresholds[16] = {
        0, 1 << 0, 1 << 1, 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
 };
 
-static inline unsigned extend(int val, int bits)
+static inline unsigned extend(int val, unsigned bits)
 {
+#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+       // GCC should ideally be able to figure out that the conditional move is better, but
+       // it doesn't for various reasons, and this is pretty important for speed, so we hardcode.
+       asm("cmp %1, %0 ; cmovl %2, %0"
+               : "+r" (val)
+               : "g" (bit_thresholds[bits]),
+                 "r" (val + (-1 << bits) + 1)
+               : "cc");
+       return val;
+#else
        if (val < bit_thresholds[bits]) {
                return val + (-1 << bits) + 1;
        } else {
                return val;
        }
+#endif
 }
 
 #endif /* !defined(_DEHUFF_H) */