facebook/zstd
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Minor changes to educational decoder

Browse Source
This commit is contained in:
Sean Purcell 2017-02-07 14:44:11 -08:00
parent f191be2fe6
commit eb52dbd4fe
1 changed files with 12 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
contrib/educational_decoder/zstd_decompress.c
View File

@ -1258,7 +1258,7 @@ static void decode_seq_table(istream_t *const in, FSE_dtable *const table,
} }
case seq_rle: { case seq_rle: {
// "RLE_Mode : it's a single code, repeated Number_of_Sequences times." // "RLE_Mode : it's a single code, repeated Number_of_Sequences times."
const u8 symb = IO_read_bits(in, 8); const u8 symb = IO_read_bytes(in, 1)[0];
FSE_init_dtable_rle(table, symb); FSE_init_dtable_rle(table, symb);
break; break;
} }
@ -1572,8 +1572,8 @@ static void free_dictionary(dictionary_t *const dict) {
#define UNALIGNED() ERROR("Attempting to operate on a non-byte aligned stream") #define UNALIGNED() ERROR("Attempting to operate on a non-byte aligned stream")
/// Reads `num` bits from a bitstream, and updates the internal offset /// Reads `num` bits from a bitstream, and updates the internal offset
static inline u64 IO_read_bits(istream_t *const in, const int num) { static inline u64 IO_read_bits(istream_t *const in, const int num) {
if (num > 64) { if (num > 64 || num <= 0) {
return -1; ERROR("Attempt to read an invalid number of bits");
} }
const size_t bytes = (num + in->bit_offset + 7) / 8; const size_t bytes = (num + in->bit_offset + 7) / 8;
@ -1710,7 +1710,7 @@ static inline istream_t IO_make_sub_istream(istream_t *const in, size_t len) {
static inline u64 read_bits_LE(const u8 *src, const int num, static inline u64 read_bits_LE(const u8 *src, const int num,
const size_t offset) { const size_t offset) {
if (num > 64) { if (num > 64) {
return -1; ERROR("Attempt to read an invalid number of bits");
} }
// Skip over bytes that aren't in range // Skip over bytes that aren't in range
@ -1871,6 +1871,11 @@ static size_t HUF_decompress_4stream(const HUF_dtable *const dtable,
return total_output; return total_output;
} }
/// Initializes a Huffman table using canonical Huffman codes
/// For more explanation on canonical Huffman codes see
/// http://www.cs.uofs.edu/~mccloske/courses/cmps340/huff_canonical_dec2015.html
/// Codes within a level are allocated in symbol order (i.e. smaller symbols get
/// earlier codes)
static void HUF_init_dtable(HUF_dtable *const table, const u8 *const bits, static void HUF_init_dtable(HUF_dtable *const table, const u8 *const bits,
const int num_symbs) { const int num_symbs) {
memset(table, 0, sizeof(HUF_dtable)); memset(table, 0, sizeof(HUF_dtable));
@ -2004,6 +2009,9 @@ static void HUF_copy_dtable(HUF_dtable *const dst,
/******* END HUFFMAN PRIMITIVES ***********************************************/ /******* END HUFFMAN PRIMITIVES ***********************************************/
/******* FSE PRIMITIVES *******************************************************/ /******* FSE PRIMITIVES *******************************************************/
/// For more description of FSE see
/// https://github.com/Cyan4973/FiniteStateEntropy/
/// Allow a symbol to be decoded without updating state /// Allow a symbol to be decoded without updating state
static inline u8 FSE_peek_symbol(const FSE_dtable *const dtable, static inline u8 FSE_peek_symbol(const FSE_dtable *const dtable,
const u16 state) { const u16 state) {