@ -10,7 +10,6 @@
/// used to generate up a [u32; 256] lookup table in `crc32`. this computes
/// used to generate up a [u32; 256] lookup table in `crc32`. this computes
/// the table on demand for a given "index" `i`
/// the table on demand for a given "index" `i`
#[ rustfmt::skip ]
const fn table_fn ( i : u32 ) -> u32 {
const fn table_fn ( i : u32 ) -> u32 {
let mut out = i ;
let mut out = i ;
@ -49,40 +48,6 @@ pub const fn crc32(buf: &[u8]) -> u32 {
crc32_seed ( buf , 0 )
crc32_seed ( buf , 0 )
}
}
/// Calculate crc32 checksum, using provided `seed` as the initial state, instead of the
/// default initial state of `0u32`.
///
/// # Examples
///
/// Calculating the checksum from several parts of a larger input:
///
/// ```
/// const BYTES: &[u8] = "The quick brown fox jumps over the lazy dog".as_bytes();
///
/// let mut cksum = 0u32;
///
/// cksum = const_crc32::crc32_seed(&BYTES[0..10], cksum);
/// cksum = const_crc32::crc32_seed(&BYTES[10..15], cksum);
/// cksum = const_crc32::crc32_seed(&BYTES[15..], cksum);
///
/// assert_eq!(cksum, const_crc32::crc32(BYTES));
/// ```
///
/// Using separate seeds for different kinds of data, to produce different checksums depending
/// on what kind of data the bytes represent:
///
/// ```
/// const THING_ONE_SEED: u32 = 0xbaaaaaad_u32;
/// const THING_TWO_SEED: u32 = 0x2bad2bad_u32;
///
/// let thing_one_bytes = "bump! thump!".as_bytes();
/// let thing_two_bytes = "thump! bump!".as_bytes();
///
/// let thing_one_cksum = const_crc32::crc32_seed(thing_one_bytes, THING_ONE_SEED);
/// let thing_two_cksum = const_crc32::crc32_seed(thing_two_bytes, THING_TWO_SEED);
///
/// assert_ne!(thing_one_cksum, thing_two_cksum);
/// ```
#[ inline ]
#[ inline ]
pub const fn crc32_seed ( buf : & [ u8 ] , seed : u32 ) -> u32 {
pub const fn crc32_seed ( buf : & [ u8 ] , seed : u32 ) -> u32 {
let mut out = ! seed ;
let mut out = ! seed ;
@ -102,10 +67,12 @@ mod tests {
fn crc32_compute_table ( ) -> [ u32 ; 256 ] {
fn crc32_compute_table ( ) -> [ u32 ; 256 ] {
let mut crc32_table = [ 0 ; 256 ] ;
let mut crc32_table = [ 0 ; 256 ] ;
for n in 0 .. 256_ u32 {
for n in 0 .. 256 {
crc32_table [ n as usize ] = ( 0 .. 8 ) . fold ( n , | acc , _ | match acc & 1 {
crc32_table [ n as usize ] = ( 0 .. 8 ) . fold ( n as u32 , | acc , _ | {
1 = > 0xedb88320 ^ ( acc > > 1 ) ,
match acc & 1 {
_ = > acc > > 1 ,
1 = > 0xedb88320 ^ ( acc > > 1 ) ,
_ = > acc > > 1 ,
}
} ) ;
} ) ;
}
}
@ -115,7 +82,7 @@ mod tests {
#[ test ]
#[ test ]
fn check_table_fn_against_example_code ( ) {
fn check_table_fn_against_example_code ( ) {
let table = crc32_compute_table ( ) ;
let table = crc32_compute_table ( ) ;
for i in 0 .. 256 {
for i in 0 .. 256 {
assert_eq! ( table [ i ] , table_fn ( i as u32 ) ) ;
assert_eq! ( table [ i ] , table_fn ( i as u32 ) ) ;
}
}
}
}
@ -127,28 +94,6 @@ mod tests {
assert_eq! ( crc32 ( BYTES ) , crc32fast ::hash ( BYTES ) ) ;
assert_eq! ( crc32 ( BYTES ) , crc32fast ::hash ( BYTES ) ) ;
}
}
#[ test ]
fn use_seed_to_checksum_from_partial_inputs ( ) {
const BYTES : & [ u8 ] = "The quick brown fox jumps over the lazy dog" . as_bytes ( ) ;
let mut cksum = crc32 ( & BYTES [ 0 .. 10 ] ) ;
cksum = crc32_seed ( & BYTES [ 10 .. ] , cksum ) ;
assert_eq! ( cksum , crc32 ( BYTES ) ) ;
}
#[ test ]
fn use_seed_to_checksum_from_many_chunks ( ) {
let mut buf = [ 0 u8 ; 1024 ] ;
let mut rng = thread_rng ( ) ;
rng . fill ( & mut buf [ .. ] ) ;
let mut cksum = 0 ;
for chunk in buf [ .. ] . chunks ( 7 ) {
cksum = crc32_seed ( chunk , cksum ) ;
}
assert_eq! ( cksum , crc32 ( & buf [ .. ] ) ) ;
}
#[ test ]
#[ test ]
fn check_random_inputs_against_crc32_fast ( ) {
fn check_random_inputs_against_crc32_fast ( ) {
const N_ITER : usize = 100 ;
const N_ITER : usize = 100 ;