Skip to content

Latest commit

 

History

History
73 lines (49 loc) · 3.03 KB

pack.md

File metadata and controls

73 lines (49 loc) · 3.03 KB
Raw

Bit Packing API

The bit packing API provides a simple way of packing integers into data buffers. The integers are not aligned to byte or word boundaries. The packing functions write the data to either memory or a file, and the unpacking functions extract that data to integers.

Bit Packing

Bits can be packed into either a memory using ptr or a file using file. The byte and off values are used to track the status of the bit packing. They must be initialized to zero prior to the first packing call.

void pack_int(void **ptr, uint8_t *byte, uint8_t *off, int val, unsigned int width);
void pack_uint(void **ptr, uint8_t *byte, uint8_t *off, unsigned int val, unsigned int width);

The pack_int and pack_uint pack an integer of size width into the memory pointed to by ptr. The pointer ptr will be incremented as necessary.

void pack_flush(void **ptr, uint8_t *byte, uint8_t *off);

The pack_flush_ call writes any pending bytes in byte to the memory of ptr. After completion, the pointer will be aligned with no pending data in byte and off.

void fpack_int(FILE *file, uint8_t *byte, uint8_t *off, int val, unsigned int width);
void fpack_uint(FILE *file, uint8_t *byte, uint8_t *off, unsigned int val, unsigned int width);
void fpack_flush(FILE *file, uint8_t *byte, uint8_t *off);

The fpack_int, fpack_uint, and fpack_flush pack and write data directly to a file referenced by file. The fpack_flush call is necessary to call prior to closing the file to guarantee any partial data from byte is written.

Bit Unpacking

Arbitrary width numbers are unpacked into meomry using ptr or a file using file. The byte and off values track partially unpacked bits, and they must be initialized to zero prior to the first unpacking call.

int unpack_int(void **ptr, uint8_t *byte, uint8_t *off, unsigned int width);
unsigned int unpack_uint(void **ptr, uint8_t *byte, uint8_t *off, unsigned int width);

The unpack_int and unpack_uint functions read integers of size width from the the memory pointed to by ptr. The pointer ptr will be incremented as necessary.

void unpack_align(void **ptr, uint8_t *byte, uint8_t *off);

The unpack_align function is used to realign the unpacking to a byte boundry. Any pending data on byte will be dropped.

int funpack_int(FILE *file, uint8_t *byte, uint8_t *off, unsigned int width);
unsigned int funpack_uint(FILE *file, uint8_t *byte, uint8_t *off, unsigned int width);
void funpack_align(FILE *file, uint8_t *byte, uint8_t *off);

The funpack_int, funpack_uint, and funpack_flush are file-based equivalents for unpacking data.

Sign Extending

static inline unsigned int pack_uext(unsigned int val, int bits)
static inline int pack_sext(int val, int bits)

The pack_uext function takes an unsigned integer val and zeros the upper bits so that the returned value is bits wide.

The pack_sext function takes a signed integetr val and sign extends the upper bits so that the returned value is bits wide.