lfg.h File Reference

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

Go to the source code of this file.

Data Structures
struct	ngc_lfg_ctx
	LFG context holding the 521-word circular buffer and byte position. More...

Macros
#define	NGC_LFG_K   521
	LFG buffer size (number of uint32 words in state).
#define	NGC_LFG_J   32
	LFG second tap.
#define	NGC_LFG_SEED_SIZE   17
	Number of uint32 words needed to seed the LFG.

Functions
void	ngc_lfg_set_seed (struct ngc_lfg_ctx *ctx, const uint32_t seed[17])
	Initialize the LFG from a 17-word big-endian seed.
void	ngc_lfg_get_bytes (struct ngc_lfg_ctx *ctx, uint8_t *out, size_t count)
	Generate count bytes of junk data into out.
size_t	ngc_lfg_get_seed (const uint8_t *data, size_t size, size_t data_offset, uint32_t seed_out[17])
	Try to extract the LFG seed from a chunk of data.

Macro Definition Documentation

NGC_LFG_J

#define NGC_LFG_J   32

LFG second tap.

Definition at line 35 of file lfg.h.

Referenced by lfg_backward(), and lfg_forward().

NGC_LFG_K

#define NGC_LFG_K   521

LFG buffer size (number of uint32 words in state).

Definition at line 34 of file lfg.h.

Referenced by lfg_backward(), lfg_forward(), lfg_initialize(), lfg_reinitialize(), ngc_lfg_get_bytes(), and ngc_lfg_get_seed().

NGC_LFG_SEED_SIZE

#define NGC_LFG_SEED_SIZE   17

Number of uint32 words needed to seed the LFG.

Definition at line 36 of file lfg.h.

Referenced by lfg_initialize(), lfg_reinitialize(), ngc_lfg_get_seed(), ngc_lfg_set_seed(), ngcw_deserialize_junk_map(), ngcw_regenerate_junk_sector(), ngcw_serialize_junk_map(), and wii_reconstruct_group_junk().

Function Documentation

ngc_lfg_get_bytes()

void ngc_lfg_get_bytes	(	struct ngc_lfg_ctx *	ctx,
		uint8_t *	out,
		size_t	count )

Generate count bytes of junk data into out.

Parameters

ctx	LFG context (must be initialized via ngc_lfg_set_seed).
out	Output buffer to fill.
count	Number of bytes to generate.

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

Definition at line 82 of file lfg.c.

References ngc_lfg_ctx::buffer, lfg_forward(), NGC_LFG_K, and ngc_lfg_ctx::position_bytes.

Referenced by ngcw_regenerate_junk_sector(), and wii_reconstruct_group_junk().

ngc_lfg_get_seed()

size_t ngc_lfg_get_seed	(	const uint8_t *	data,
		size_t	size,
		size_t	data_offset,
		uint32_t	seed_out[17] )

Try to extract the LFG seed from a chunk of data.

Attempts to reverse-engineer the 17-word seed from a buffer of suspected PRNG output. Requires at least NGC_LFG_K * 4 = 2084 bytes of contiguous PRNG output aligned to uint32 boundaries.

Parameters

data	Pointer to the data to test.
size	Number of bytes available.
data_offset	Byte offset of data[0] within its LFG block (0x8000-aligned for Wii, arbitrary for GC).
seed_out	If successful, receives the 17-word seed (big-endian).

Returns

The number of consecutive bytes from data[0] that match the LFG. Returns 0 if the data does not look like junk.

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

< LFG buffer size (number of uint32 words in state).

Definition at line 121 of file lfg.c.

References ngc_lfg_ctx::buffer, lfg_backward(), lfg_forward(), lfg_reinitialize(), NGC_LFG_K, NGC_LFG_SEED_SIZE, ngc_lfg_ctx::position_bytes, and swap32().

ngc_lfg_set_seed()

void ngc_lfg_set_seed	(	struct ngc_lfg_ctx *	ctx,
		const uint32_t	seed[17] )

Initialize the LFG from a 17-word big-endian seed.

Parameters

ctx	LFG context to initialize.
seed	Array of 17 uint32 seed words (big-endian).

< Number of uint32 words needed to seed the LFG.

Definition at line 73 of file lfg.c.

References ngc_lfg_ctx::buffer, lfg_initialize(), NGC_LFG_SEED_SIZE, ngc_lfg_ctx::position_bytes, and swap32().

Referenced by ngcw_regenerate_junk_sector(), and wii_reconstruct_group_junk().