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/*
FILE NAME: bits.c
TITLE: Package for work with bits
DESCRIPTION: This file implements functions of the package for work
with bit strings. A bit is given by address (start address) of
byte from which counting bits starts and its displacement which
is any non negative number of bit from the start address. The
most significant bit of the start address byte has number 0.
The bit string is given by its first bit and its length in
bits.
*/
#include "bits.h"
/* This function determines that given bit string contains only zero
bits. The function retruns TRUE if all bits of given bit string
are zero or `bit_length' <= 0. Value of `bit_displacement' must be
non-negative and can be greater than CHAR_BIT. */
int
ammunition_is_zero_bit_string ( const void *start_byte, int bit_displacement,
int bit_length )
{
const unsigned char *current_byte = ( unsigned const char * )start_byte;
if ( bit_length <= 0 )
return 1 /* TRUE */;
current_byte += bit_displacement / CHAR_BIT;
bit_displacement %= CHAR_BIT;
if ( bit_length < CHAR_BIT - bit_displacement )
return ( ( ( *current_byte << bit_displacement )
& ( UCHAR_MAX << ( CHAR_BIT - bit_length ) ) )
& UCHAR_MAX ) == 0;
else
if ( bit_displacement != 0 ) {
if ( ( ( *current_byte << bit_displacement ) & UCHAR_MAX ) != 0 )
return 0 /* FALSE */;
current_byte += 1;
bit_length -= CHAR_BIT - bit_displacement;
}
_Pragma( "loopbound min 0 max 7" )
while ( bit_length >= CHAR_BIT ) {
if ( *current_byte != 0 )
return 0 /* FALSE */;
current_byte++;
bit_length -= CHAR_BIT;
}
if ( bit_length > 0 && ( *current_byte >> ( CHAR_BIT - bit_length ) ) != 0 )
return 0 /* FALSE */;
return 1 /* TRUE */;
}
/* This function sets up new value of all bits of given bit string.
This function is analog of standard C function `memset'. Value of
`bit_displacement' must be non-negative and can be greater than
CHAR_BIT. */
void
ammunition_bit_string_set ( void *start_byte, int bit_displacement, int bit,
int bit_length )
{
unsigned char *current_byte = ( unsigned char * )start_byte;
unsigned char filling_byte;
int mask;
if ( bit_length <= 0 )
return ;
bit = bit != 0; /* 1 or 0 */
filling_byte = ( bit ? UCHAR_MAX : 0 );
current_byte += bit_displacement / CHAR_BIT;
bit_displacement %= CHAR_BIT;
if ( bit_displacement != 0 ) {
mask = UCHAR_MAX << ( CHAR_BIT - bit_displacement );
if ( bit_length < CHAR_BIT - bit_displacement )
mask |= UCHAR_MAX >> ( bit_displacement + bit_length );
*current_byte = ( *current_byte & mask ) | ( filling_byte & ~mask );
current_byte += 1;
bit_length -= CHAR_BIT - bit_displacement;
}
_Pragma( "loopbound min 0 max 8" )
while ( bit_length >= CHAR_BIT ) {
*current_byte = filling_byte;
current_byte++;
bit_length -= CHAR_BIT;
}
if ( bit_length > 0 )
*current_byte
= ( *current_byte & ~( UCHAR_MAX << ( CHAR_BIT - bit_length ) ) )
| ( filling_byte & ( UCHAR_MAX << ( CHAR_BIT - bit_length ) ) );
}
/* This function copys a bit string to another bit string. This
function is analog of standard C function `memcpy'. Values of
`to_bit_displacement' and `from_bit_displacement' must be
non-negative and can be greater than CHAR_BIT. The bit string must
be non-overlapped. */
void
ammunition_bit_string_copy ( void *to, int to_bit_displacement,
const void *from, int from_bit_displacement,
int bit_length )
{
unsigned char *current_to_byte = ( unsigned char * )to;
const unsigned char *current_from_byte = ( unsigned const char * )from;
int byte;
int mask;
if ( bit_length <= 0 )
return ;
current_to_byte += to_bit_displacement / CHAR_BIT;
to_bit_displacement %= CHAR_BIT;
current_from_byte += from_bit_displacement / CHAR_BIT;
from_bit_displacement %= CHAR_BIT;
_Pragma( "loopbound min 1 max 8" )
while ( 1 ) {
byte = ( ( ( *current_from_byte << from_bit_displacement ) & UCHAR_MAX )
| ( from_bit_displacement != 0
&& bit_length > ( CHAR_BIT - from_bit_displacement )
? current_from_byte [1] >> ( CHAR_BIT - from_bit_displacement )
: 0 ) );
if ( bit_length <= CHAR_BIT )
break;
/* Shift is correct when to_bit_displacement == 0 because its
value is less than word bit size. */
*current_to_byte
= ( *current_to_byte
& ( UCHAR_MAX << ( CHAR_BIT - to_bit_displacement ) ) )
| ( byte >> to_bit_displacement );
if ( to_bit_displacement != 0 )
current_to_byte [1]
= ( current_to_byte [1] & ( UCHAR_MAX >> to_bit_displacement ) )
| ( byte << ( CHAR_BIT - to_bit_displacement ) );
bit_length -= CHAR_BIT;
current_from_byte++;
current_to_byte++;
}
/* Shift is correct when to_bit_displacement == 0 because its
value is less than word bit size. */
mask = ( ( UCHAR_MAX << ( CHAR_BIT - to_bit_displacement ) )
| ( UCHAR_MAX >> ( to_bit_displacement + bit_length ) ) );
*current_to_byte
= ( *current_to_byte & mask ) | ( ( byte >> to_bit_displacement ) & ~mask );
bit_length -= CHAR_BIT - to_bit_displacement;
if ( bit_length > 0 )
current_to_byte [1]
= ( current_to_byte [1] & ( UCHAR_MAX >> bit_length ) )
| ( ( byte << ( CHAR_BIT - to_bit_displacement ) )
& ( UCHAR_MAX << ( CHAR_BIT - bit_length ) ) );
}
/* This function copys a bit string to another bit string. Copying
starts with the last bits of the bit strings. This function is
used by function `bit_string_move'. Values of
`to_bit_displacement' and `from_bit_displacement' must be
non-negative and can be greater than CHAR_BIT. The bit string must
be non-overlapped. */
void ammunition_reverse_bit_string_copy ( void *to, int to_bit_displacement,
const void *from, int from_bit_displacement,
int bit_length )
{
unsigned char *current_to_byte = ( unsigned char * )to;
const unsigned char *current_from_byte = ( unsigned const char * )from;
int byte;
int mask;
if ( bit_length <= 0 )
return ;
to_bit_displacement += bit_length - 1;
current_to_byte += to_bit_displacement / CHAR_BIT; /* last byte */
to_bit_displacement %= CHAR_BIT; /* last bit */
from_bit_displacement += bit_length - 1;
current_from_byte += from_bit_displacement / CHAR_BIT; /* last byte */
from_bit_displacement %= CHAR_BIT; /* last bit */
_Pragma( "loopbound min 1 max 8" )
while ( 1 ) {
/* Shift is correct when to_bit_displacement == 0 because its
value is less than word bit size. */
byte = ( ( *current_from_byte >> ( CHAR_BIT - 1 - from_bit_displacement ) )
| ( ( from_bit_displacement != CHAR_BIT - 1
&& bit_length > from_bit_displacement + 1
? current_from_byte [ -1 ] << ( from_bit_displacement + 1 )
: 0 )
& UCHAR_MAX ) );
if ( bit_length <= CHAR_BIT )
break;
/* Shift is correct when to_bit_displacement == 0 because its
value is less than word bit size. */
*current_to_byte
= ( *current_to_byte & ( UCHAR_MAX >> ( to_bit_displacement + 1 ) ) )
| ( byte << ( CHAR_BIT - 1 - to_bit_displacement ) );
if ( to_bit_displacement != CHAR_BIT - 1 )
current_to_byte [-1]
= ( current_to_byte [-1]
& ( UCHAR_MAX << ( CHAR_BIT - 1 - to_bit_displacement ) ) )
| ( byte >> ( to_bit_displacement + 1 ) );
bit_length -= CHAR_BIT;
current_from_byte--;
current_to_byte--;
}
/* Shift is correct when to_bit_displacement == 0 because its
value is less than word bit size. */
mask = ( ( UCHAR_MAX >> ( to_bit_displacement + 1 ) ) |
( UCHAR_MAX << ( CHAR_BIT - 1 - to_bit_displacement
+ bit_length ) ) );
*current_to_byte
= ( *current_to_byte & mask )
| ( ( byte << ( CHAR_BIT - 1 - to_bit_displacement ) ) & ~mask );
bit_length -= to_bit_displacement + 1;
if ( bit_length > 0 )
current_to_byte [-1]
= ( current_to_byte [-1] & ( UCHAR_MAX << bit_length ) )
| ( byte >> ( to_bit_displacement + 1 )
& ( UCHAR_MAX >> ( CHAR_BIT - bit_length ) ) );
}
/* This function copys a bit string to another bit string with the aid
of functions `bit_string_copy' and `reverse_bit_string_copy'. This
function is analog of standard C function `memmove'. Values of
`to_bit_displacement' and `from_bit_displacement' must be
non-negative and can be greater than CHAR_BIT. The bit string can
be overlapped. */
void
ammunition_bit_string_move ( void *to, int to_bit_displacement,
const void *from, int from_bit_displacement,
int bit_length )
{
unsigned char *current_to_byte = ( unsigned char * )to;
const unsigned char *current_from_byte = ( unsigned const char * )from;
if ( bit_length <= 0 )
return ;
current_to_byte += to_bit_displacement / CHAR_BIT;
to_bit_displacement %= CHAR_BIT;
current_from_byte += from_bit_displacement / CHAR_BIT;
from_bit_displacement %= CHAR_BIT;
if ( current_from_byte > current_to_byte
|| ( current_from_byte == current_to_byte
&& from_bit_displacement > to_bit_displacement ) )
ammunition_bit_string_copy ( current_to_byte, to_bit_displacement,
current_from_byte, from_bit_displacement,
bit_length );
else
ammunition_reverse_bit_string_copy ( current_to_byte, to_bit_displacement,
current_from_byte,
from_bit_displacement, bit_length );
}
/* This function compares bit strings. This function is analog of
standard C function `memcmp'. The function returns 0 if the bit
strings are equal, 1 if the first bit string is greater than the
second, -1 if the first bit string is less than the first. Values
of `bit_displacement1' and `bit_displacement2' must be non-negative
and can be greater than CHAR_BIT. */
int
ammunition_bit_string_comparison ( const void *str1, int bit_displacement1,
const void *str2, int bit_displacement2,
int bit_length )
{
const unsigned char *current_byte1 = ( unsigned const char * )str1;
const unsigned char *current_byte2 = ( unsigned const char * )str2;
int byte1;
int byte2;
int mask;
if ( bit_length <= 0 )
return 0;
current_byte1 += bit_displacement1 / CHAR_BIT;
bit_displacement1 %= CHAR_BIT;
current_byte2 += bit_displacement2 / CHAR_BIT;
bit_displacement2 %= CHAR_BIT;
_Pragma( "loopbound min 1 max 284" )
while ( 1 ) {
byte1 = ( ( ( *current_byte1 << bit_displacement1 ) & UCHAR_MAX )
| ( bit_displacement1 != 0
/* Shift is correct when to_bit_displacement == 0
because its value is less than word bit size. */
&& bit_length > CHAR_BIT - bit_displacement1
? current_byte1 [1] >> ( CHAR_BIT - bit_displacement1 )
: 0 ) );
byte2 = ( ( ( *current_byte2 << bit_displacement2 ) & UCHAR_MAX )
| ( bit_displacement2 != 0
&& bit_length > CHAR_BIT - bit_displacement2
? current_byte2 [1] >> ( CHAR_BIT - bit_displacement2 )
: 0 ) );
if ( bit_length <= CHAR_BIT )
break;
if ( byte1 > byte2 )
return 1;
else
if ( byte1 < byte2 )
return -1;
bit_length -= CHAR_BIT;
current_byte2++;
current_byte1++;
}
/* Shift is correct when to_bit_displacement == 0 because its value
is less than word bit size. */
mask = UCHAR_MAX << ( CHAR_BIT - bit_length );
if ( ( byte1 & mask ) > ( byte2 & mask ) )
return 1;
else
if ( ( byte1 & mask ) < ( byte2 & mask ) )
return -1;
else
return 0;
}
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