Add code for efficient (?) Huffman decoding.

[fjl] / input.h

diff --git a/input.h b/input.h
index 28c5f0b8530e820101063cef9c0ab83ea6aa0748..19315e54ab3c357ceaf1f16f96f310caace75b76 100644 (file)
--- a/input.h
+++ b/input.h
@@ -17,15 +17,17 @@ static inline bitreservoir_fill_t read_bitreservoir_fill(uint8_t* source)
        return ntohl(*(bitreservoir_fill_t*)(source));
 }
 
-static const unsigned bitreservoir_size = 8 * sizeof(bitreservoir_t);
-static const unsigned bitreservoir_fill_size = 8 * sizeof(bitreservoir_fill_t);
-static const unsigned bytereservoir_size = 4096;
+static const unsigned BITRESERVOIR_SIZE = 8 * sizeof(bitreservoir_t);
+static const unsigned BITRESERVOIR_FILL_SIZE = 8 * sizeof(bitreservoir_fill_t);
+static const unsigned BYTERESERVOIR_SIZE = 4096;
 
-// A function to read bytes from some input source.
+// A function to read bytes from some input source. The bytes should be
+// already unstuffed (and thus without markers).
 // A return value of -1 indicates error, a return value of 0 indicates EOF.
 typedef ssize_t (input_func_t)(void*, uint8_t*, size_t);
 
-struct data_source {
+// A data source for efficient reading of bit-level data.
+struct bit_source {
        // Short-term bit reservoir; holds up to 64 bits. When it's empty,
        // it needs to get refilled from the medium-term bit reservoir.
        bitreservoir_t bits;
@@ -41,19 +43,19 @@ struct data_source {
        input_func_t* input_func;
        void* userdata;
 };
-       
-void init_data_source(struct data_source* source, input_func_t* input_func, void* userdata);
+
+void init_bit_source(struct bit_source* source, input_func_t* input_func, void* userdata);
 
 // Internal function. Do not use.
-void possibly_refill_slow_path(struct data_source* source, unsigned num_bits);
+void possibly_refill_slow_path(struct bit_source* source, unsigned num_bits);
 
 // Make sure there's at least NUM_BITS available in the short-term bit reservoir.
 // You usually want to call this before read_bits(). The reason it's separate
 // is that if you want two reads and you know the size of both, it's faster to
 // refill A+B, read A, read B than refill A, read A, refill B, read B.
-static inline void possibly_refill(struct data_source* source, unsigned num_bits)
+static inline void possibly_refill(struct bit_source* source, unsigned num_bits)
 {
-       assert(num_bits <= bitreservoir_fill_size + 1);
+       assert(num_bits <= BITRESERVOIR_FILL_SIZE + 1);
 
        if (source->bits_available >= num_bits) {
                // Fast path (~90% of invocations?)
@@ -61,13 +63,13 @@ static inline void possibly_refill(struct data_source* source, unsigned num_bits
        }
 
        // Slower path (~99% of remaining invocations?)
-       assert(source->bits_available + bitreservoir_fill_size < bitreservoir_size);
+       assert(source->bits_available + BITRESERVOIR_FILL_SIZE < BITRESERVOIR_SIZE);
        if (source->bytes_available >= sizeof(bitreservoir_fill_t)) {
                bitreservoir_fill_t fill = read_bitreservoir_fill(source->bytes);
                source->bytes += sizeof(bitreservoir_fill_t);
                source->bytes_available -= sizeof(bitreservoir_fill_t);
-               source->bits |= (bitreservoir_t)fill << (bitreservoir_size - bitreservoir_fill_size - source->bits_available);
-               source->bits_available += bitreservoir_fill_size;
+               source->bits |= (bitreservoir_t)fill << (BITRESERVOIR_SIZE - BITRESERVOIR_FILL_SIZE - source->bits_available);
+               source->bits_available += BITRESERVOIR_FILL_SIZE;
                return;
        }
 
@@ -76,13 +78,19 @@ static inline void possibly_refill(struct data_source* source, unsigned num_bits
        possibly_refill_slow_path(source, num_bits);
 }
 
-static inline unsigned read_bits(struct data_source* source, unsigned num_bits)
+static inline unsigned read_bits(struct bit_source* source, unsigned num_bits)
 {
        assert(source->bits_available >= num_bits);
-       unsigned ret = (source->bits >> (bitreservoir_size - num_bits));
+       unsigned ret = (source->bits >> (BITRESERVOIR_SIZE - num_bits));
        source->bits <<= num_bits;
        source->bits_available -= num_bits;
        return ret;
 }
 
+static inline unsigned peek_bits(struct bit_source* source, unsigned num_bits)
+{
+       assert(source->bits_available >= num_bits);
+       return (source->bits >> (BITRESERVOIR_SIZE - num_bits));
+}
+
 #endif /* !defined(_INPUT_H) */