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-rw-r--r--include/lib/inflate.h1
-rw-r--r--src/lib/inflate.cc104
2 files changed, 61 insertions, 44 deletions
diff --git a/include/lib/inflate.h b/include/lib/inflate.h
index 575be4a..af2b4f7 100644
--- a/include/lib/inflate.h
+++ b/include/lib/inflate.h
@@ -16,6 +16,7 @@
#define DEFLATE_ERR_OUTPUT_LENGTH (-6)
#define DEFLATE_ERR_FCHECK (-7)
#define DEFLATE_ERR_NLEN (-8)
+#define DEFLATE_ERR_HUFFMAN (-9)
int16_t inflate(unsigned char *input_buf, uint16_t input_len,
unsigned char *output_buf, uint16_t output_len);
diff --git a/src/lib/inflate.cc b/src/lib/inflate.cc
index 8e83453..e79c4fb 100644
--- a/src/lib/inflate.cc
+++ b/src/lib/inflate.cc
@@ -88,36 +88,33 @@ uint8_t deflate_hc_lengths[19];
/*
* Code lengths of the literal/length and distance alphabets.
+ * up to 286 literal/length codes + up to 32 distance codes.
*/
uint8_t deflate_lld_lengths[318];
/*
- * Assumptions:
- * * huffman code length is limited to 11 bits
- * * there are no more than 255 huffman codes with the same length
- *
- * Rationale: longer huffman codes might appear when handling large data
- * sets. We don't do that; instead, we expect the uncompressed source to
- * be no more than a few kB of data.
- */
-
-/*
* Bit length counts and next code entries for Literal/Length alphabet.
* Combined with the code lengths in deflate_lld_lengths, these make up the
* Literal/Length alphabet. See the algorithm in RFC 1951 section 3.2.2 for
* details.
*
- * In deflate, these variables are also used for the huffman alphabet in
- * dynamic huffman blocks.
+ * Assumption: There are no more than 255 huffman codes with the same length.
+ * As the largest alphabet (the literal/length alphabet) contains just 288
+ * codes in total, this should be reasonable.
+ *
+ * These variables are also used for the huffman alphabet in dynamic huffman
+ * blocks.
*/
-uint8_t deflate_bl_count_ll[12];
-uint16_t deflate_next_code_ll[12];
+uint8_t deflate_bl_count_ll[16];
+uint16_t deflate_next_code_ll[16];
/*
- * Bit length counts and next code entries for Distance alphabet.
+ * Bit length counts and next code entries for Distance alphabet. Note that,
+ * even though there are just 30 different distance codes, individual
+ * codes may be up to 16 bits long.
*/
-uint8_t deflate_bl_count_d[12];
-uint16_t deflate_next_code_d[12];
+uint8_t deflate_bl_count_d[16];
+uint16_t deflate_next_code_d[16];
static uint16_t deflate_rev_word(uint16_t word, uint8_t bits)
{
@@ -132,7 +129,7 @@ static uint16_t deflate_rev_word(uint16_t word, uint8_t bits)
return ret;
}
-static uint8_t deflate_bitmask(uint8_t bit_count)
+static uint16_t deflate_bitmask(uint8_t bit_count)
{
return (1 << bit_count) - 1;
}
@@ -168,7 +165,7 @@ static void deflate_build_alphabet(uint8_t * lengths, uint16_t size,
uint16_t i;
uint16_t code = 0;
uint16_t max_len = 0;
- for (i = 0; i < 12; i++) {
+ for (i = 0; i < 16; i++) {
bl_count[i] = 0;
}
@@ -187,11 +184,17 @@ static void deflate_build_alphabet(uint8_t * lengths, uint16_t size,
}
}
+/*
+ * This function trades speed for low memory requirements. Instead of building
+ * an actual huffman tree (at a cost of about 650 Bytes of RAM), we iterate
+ * through the code lengths whenever we have found a huffman code. This is
+ * very slow, but memory-efficient.
+ */
static uint16_t deflate_huff(uint8_t * lengths, uint16_t size,
uint8_t * bl_count, uint16_t * next_code)
{
uint16_t next_word = deflate_get_word();
- for (uint8_t num_bits = 1; num_bits < 12; num_bits++) {
+ for (uint8_t num_bits = 1; num_bits < 16; num_bits++) {
uint16_t next_bits = deflate_rev_word(next_word, num_bits);
if (bl_count[num_bits] && next_bits >= next_code[num_bits]
&& next_bits < next_code[num_bits] + bl_count[num_bits]) {
@@ -202,6 +205,7 @@ static uint16_t deflate_huff(uint8_t * lengths, uint16_t size,
}
uint8_t len_pos = next_bits;
uint8_t cur_pos = next_code[num_bits];
+ // This is slow, but memory-efficient
for (uint16_t i = 0; i < size; i++) {
if (lengths[i] == num_bits) {
if (cur_pos == len_pos) {
@@ -232,6 +236,8 @@ static int8_t deflate_huffman(uint8_t * ll_lengths, uint16_t ll_size,
deflate_output_now++;
} else if (code == 256) {
return 0;
+ } else if (code == 65535) {
+ return DEFLATE_ERR_HUFFMAN;
} else {
uint16_t len_val = deflate_length_offsets[code - 257];
uint8_t extra_bits = deflate_length_bits[code - 257];
@@ -264,7 +270,10 @@ static int8_t deflate_huffman(uint8_t * ll_lengths, uint16_t ll_size,
static int8_t deflate_uncompressed()
{
- deflate_input_now++;
+ if (deflate_bit_offset) {
+ deflate_input_now++;
+ deflate_bit_offset = 0;
+ }
uint16_t len =
((uint16_t) deflate_input_now[1] << 8) + deflate_input_now[0];
uint16_t nlen =
@@ -334,7 +343,8 @@ static int8_t deflate_dynamic_huffman()
uint16_t items_processed = 0;
while (items_processed < hlit + hdist) {
uint8_t code =
- deflate_huff(deflate_hc_lengths, 19, deflate_bl_count_ll,
+ deflate_huff(deflate_hc_lengths, sizeof(deflate_hc_lengths),
+ deflate_bl_count_ll,
deflate_next_code_ll);
if (code == 16) {
uint8_t copy_count = 3 + deflate_get_bits(2);
@@ -373,36 +383,42 @@ static int8_t deflate_dynamic_huffman()
int16_t inflate(unsigned char *input_buf, uint16_t input_len,
unsigned char *output_buf, uint16_t output_len)
{
- //uint8_t is_final = input_buf[0] & 0x01;
- uint8_t block_type = (input_buf[0] & 0x06) >> 1;
- int8_t ret;
-
deflate_input_now = input_buf;
deflate_input_end = input_buf + input_len;
- deflate_bit_offset = 3;
+ deflate_bit_offset = 0;
deflate_output_now = output_buf;
deflate_output_end = output_buf + output_len;
- switch (block_type) {
- case 0:
- ret = deflate_uncompressed();
- break;
- case 1:
- ret = deflate_static_huffman();
- break;
- case 2:
- ret = deflate_dynamic_huffman();
- break;
- default:
- return DEFLATE_ERR_BLOCK;
- }
+ while (1) {
+ uint8_t block_type = deflate_get_bits(3);
+ uint8_t is_final = block_type & 0x01;
+ int8_t ret;
+
+ block_type >>= 1;
+
+ switch (block_type) {
+ case 0:
+ ret = deflate_uncompressed();
+ break;
+ case 1:
+ ret = deflate_static_huffman();
+ break;
+ case 2:
+ ret = deflate_dynamic_huffman();
+ break;
+ default:
+ return DEFLATE_ERR_BLOCK;
+ }
- if (ret < 0) {
- return ret;
- }
+ if (ret < 0) {
+ return ret;
+ }
- return deflate_output_now - output_buf;
+ if (is_final) {
+ return deflate_output_now - output_buf;
+ }
+ }
}
int16_t inflate_zlib(unsigned char *input_buf, uint16_t input_len,