Skip to content
GitLab
Menu
Projects
Groups
Snippets
Help
Help
Support
Community forum
Keyboard shortcuts
?
Submit feedback
Contribute to GitLab
Sign in / Register
Toggle navigation
Menu
Open sidebar
ISC Open Source Projects
BIND
Commits
21cbbc3e
Commit
21cbbc3e
authored
Dec 15, 1999
by
Michael Graff
Browse files
document functions. Add isc_lfsr_init() and unimplemented isc_lfsr_findlfsr()
parent
87526776
Changes
2
Hide whitespace changes
Inline
Side-by-side
lib/isc/include/isc/lfsr.h
View file @
21cbbc3e
...
...
@@ -26,7 +26,7 @@
*/
typedef
struct
{
isc_uint32_t
state
;
/* previous state */
isc_uint32_
t
bits
;
/* length */
unsigned
in
t
bits
;
/* length */
isc_uint32_t
tap
;
/* bit taps */
}
isc_lfsr_t
;
...
...
@@ -39,10 +39,81 @@ extern isc_lfsr_t isc_lfsr_standard[];
ISC_LANG_BEGINDECLS
/*
* In all these functions it is important that the caller only use as many
* bits as the LFSR has state. Also, it isn't guaranteed that an LFSR of
* bit length 32 will have 2^32 unique states before repeating.
*/
isc_lfsr_t
*
isc_lfsr_findlfsr
(
unsigned
int
bits
);
/*
* Find an LFSR that has at least "bits" of state.
*
* Requires:
*
* 8 <= bits <= 32
*
* Returns:
*
* NULL if no LFSR can be found.
*
* If NON-null, it points to the first LFSR in the standard LFSR table
* that satisfies the requirements.
*/
void
isc_lfsr_init
(
isc_lfsr_t
*
lfsr
,
isc_uint32_t
state
,
unsigned
int
bits
,
isc_uint32_t
tap
);
/*
* Initialize an LFSR.
*
* Note:
*
* Putting untrusted values into this function will cause the LFSR to
* generate (perhaps) non-maximal length sequences.
*
* Requires:
*
* lfsr != NULL
*
* 8 <= bits <= 32
*
* tap != 0
*/
isc_uint32_t
isc_lfsr_generate
(
isc_lfsr_t
*
lfsr
);
/*
* Return the next state in the LFSR.
*
* Requires:
*
* lfsr be valid.
*/
isc_uint32_t
isc_lfsr_skipgenerate
(
isc_lfsr_t
*
lfsr
,
unsigned
int
skip
);
/*
* Skip "skip" states, then return the next state after that.
*
* Requiremens are the same as for isc_lfsr_generate(), above.
*/
isc_uint32_t
isc_lfsr_lfsrskipgenerate
(
isc_lfsr_t
*
lfsr1
,
isc_lfsr_t
*
lfsr2
,
unsigned
int
skipbits
);
/*
* Given two LFSRs, use the current state from each to skip entries in the
* other. The next states are then xor'd together and returned.
*
* Notes:
*
* Since the current state from each of the LFSRs is used to skip
* state in the other, it is important that no state be leaked
* from either LFSR.
*
* Requires:
*
* lfsr1 and lfsr2 be valid.
*
* 1 <= skipbits <= 31
*/
ISC_LANG_ENDDECLS
...
...
lib/isc/lfsr.c
View file @
21cbbc3e
...
...
@@ -23,6 +23,7 @@
/*
* Any LFSR added to this table needs to have a large period.
* Entries should be added from longest bit state to smallest bit state.
* XXXMLG Need to pull some from Applied Crypto.
*/
isc_lfsr_t
isc_lfsr_standard
[]
=
{
{
0
,
32
,
0x80000057U
},
/* 32-bit, x^31 + x^6 + x^4 + x^2 + x + 1 */
...
...
@@ -35,6 +36,25 @@ isc_lfsr_t isc_lfsr_standard[] = {
#define VALID_LFSR(x) (x != NULL)
isc_lfsr_t
*
isc_lfsr_findlfsr
(
unsigned
int
bits
)
{
return
(
NULL
);
/* XXXMLG implement? */
}
void
isc_lfsr_init
(
isc_lfsr_t
*
lfsr
,
isc_uint32_t
state
,
unsigned
int
bits
,
isc_uint32_t
tap
)
{
REQUIRE
(
VALID_LFSR
(
lfsr
));
REQUIRE
(
8
<=
bits
&&
bits
<=
32
);
REQUIRE
(
tap
!=
0
);
lfsr
->
state
=
state
;
lfsr
->
bits
=
bits
;
lfsr
->
tap
=
tap
;
}
/*
* Return the next state of the lfsr.
*/
...
...
Write
Preview
Supports
Markdown
0%
Try again
or
attach a new file
.
Attach a file
Cancel
You are about to add
0
people
to the discussion. Proceed with caution.
Finish editing this message first!
Cancel
Please
register
or
sign in
to comment