Sweden-Number/ipc/bit_array.c

282 lines
6.2 KiB
C

/***************************************************************************
* Copyright 1995, Technion, Israel Institute of Technology
* Electrical Eng, Software Lab.
* Author: Michael Veksler.
***************************************************************************
* File: bit_array.c
* Purpose : manipulate array of bits
* Portability: This is not completely portable, non CISC arcitectures
* Might not have atomic Clear/Set/Toggle bit. On those
* architectures semaphores should be used.
* Big Endian Concerns: This code is big endian compatible,
* but the byte order will be different (i.e. bit 0 will be
* located in byte 3).
***************************************************************************
*/
#ifdef CONFIG_IPC
/*
** uncoment the following line to disable assertions,
** this may boost performance by up to 50%
*/
/* #define NDEBUG */
#if defined(linux) && !defined(NO_ASM)
#define HAS_BITOPS
#endif
#include <stdio.h>
#include <assert.h>
#include "bit_array.h"
#ifdef HAS_BITOPS
#define inline __inline__ /* So we can compile with -ansi */
#include <asm/bitops.h>
#else
static __inline__ int clear_bit(int bit, int *mem);
static __inline__ int set_bit(int bit, int *mem);
#endif /* HAS_BITOPS */
#define INT_NR(bit_nr) ((bit_nr) >> INT_LOG2)
#define INT_COUNT(bit_count) INT_NR( bit_count + BITS_PER_INT - 1 )
#define BIT_IN_INT(bit_nr) ((bit_nr) & (BITS_PER_INT - 1))
#if !defined(HAS_BITOPS)
/* first_zero maps bytes value to the index of first zero bit */
static char first_zero[256];
static int arrays_initialized=0;
/*
** initialize static arrays used for bit operations speedup.
** Currently initialized: first_zero[256]
** set "arrays_initialized" to inidate that arrays where initialized
*/
static void initialize_arrays()
{
int i;
int bit;
for (i=0 ; i<256 ; i++) {
/* find the first zero bit in `i' */
for (bit=0 ; bit < BITS_PER_BYTE ; bit++)
/* break if the bit is zero */
if ( ( (1 << bit) & i )
== 0)
break;
first_zero[i]= bit;
}
arrays_initialized=1;
}
/*
** Find first zero bit in the integer.
** Assume there is at least one zero.
*/
static __inline__ int find_zbit_in_integer(unsigned int integer)
{
int i;
/* find the zero bit */
for (i=0 ; i < sizeof(int) ; i++, integer>>=8) {
int byte= integer & 0xff;
if (byte != 0xff)
return ( first_zero[ byte ]
+ (i << BYTE_LOG2) );
}
assert(0); /* never reached */
return 0;
}
/* return -1 on failure */
static __inline__ int find_first_zero_bit(unsigned *array, int bits)
{
unsigned int integer;
int i;
int bytes=INT_COUNT(bits);
if (!arrays_initialized)
initialize_arrays();
for ( i=bytes ; i ; i--, array++) {
integer= *array;
/* test if integer contains a zero bit */
if (integer != ~0U)
return ( find_zbit_in_integer(integer)
+ ((bytes-i) << INT_LOG2) );
}
/* indicate failure */
return -1;
}
static __inline__ int test_bit(int pos, unsigned *array)
{
unsigned int integer;
int bit = BIT_IN_INT(pos);
integer= array[ pos >> INT_LOG2 ];
return ( (integer & (1 << bit)) != 0
? 1
: 0 ) ;
}
/*
** The following two functions are x86 specific ,
** other processors will need porting
*/
/* inputs: bit number and memory address (32 bit) */
/* output: Value of the bit before modification */
static __inline__ int clear_bit(int bit, int *mem)
{
int ret;
__asm__("xor %1,%1
btrl %2,%0
adcl %1,%1"
:"=m" (*mem), "=&r" (ret)
:"r" (bit));
return (ret);
}
static __inline__ int set_bit(int bit, int *mem)
{
int ret;
__asm__("xor %1,%1
btsl %2,%0
adcl %1,%1"
:"=m" (*mem), "=&r" (ret)
:"r" (bit));
return (ret);
}
#endif /* !deined(HAS_BITOPS) */
/* AssembleArray: assemble an array object using existing data */
bit_array *AssembleArray(bit_array *new_array, unsigned int *buff, int bits)
{
assert(new_array!=NULL);
assert(buff!=NULL);
assert(bits>0);
assert((1 << INT_LOG2) == BITS_PER_INT); /* if fails, redefine INT_LOG2 */
new_array->bits=bits;
new_array->array=buff;
return new_array;
}
/* ResetArray: reset the bit array to zeros */
int ResetArray(bit_array *bits)
{
int i;
int *p;
assert(bits!=NULL);
assert(bits->array!=NULL);
for(i= INT_COUNT(bits->bits), p=bits->array; i ; p++, i--)
*p=0;
return 1;
}
/* VacantBit: find a vacant (zero) bit in the array,
* Return: Bit index on success, -1 on failure.
*/
int VacantBit(bit_array *bits)
{
int bit;
assert(bits!=NULL);
assert(bits->array!=NULL);
bit= find_first_zero_bit(bits->array, bits->bits);
if (bit >= bits->bits) /* failed? */
return -1;
return bit;
}
int SampleBit(bit_array *bits, int i)
{
assert(bits != NULL);
assert(bits->array != NULL);
assert(i >= 0 && i < bits->bits);
return ( test_bit(i,bits->array) != 0
? 1
: 0
);
}
/*
** Use "compare and exchange" mechanism to make sure
** that bits are not modified while "integer" value
** is calculated.
**
** This may be the slowest technique, but it is the most portable
** (Since most architectures have compare and exchange command)
*/
int AssignBit(bit_array *bits, int bit_nr, int val)
{
int ret;
assert(bits != NULL);
assert(bits->array != NULL);
assert(val==0 || val==1);
assert(bit_nr >= 0 && bit_nr < bits->bits);
if (val==0)
ret= clear_bit(BIT_IN_INT(bit_nr), &bits->array[ INT_NR(bit_nr) ]);
else
ret= set_bit(BIT_IN_INT(bit_nr), &bits->array[ INT_NR(bit_nr) ]);
return ( (ret!=0) ? 1 : 0);
}
/*
** Allocate a free bit (==0) and make it used (==1).
** This operation is guaranteed to resemble an atomic instruction.
**
** Return: allocated bit index, or -1 on failure.
**
** There is a crack between locating free bit, and allocating it.
** We assign 1 to the bit, test it was not '1' before the assignment.
** If it was, restart the seek and assign cycle.
**
*/
int AllocateBit(bit_array *bits)
{
int bit_nr;
int orig_bit;
assert(bits != NULL);
assert(bits->array != NULL);
do {
bit_nr= VacantBit(bits);
if (bit_nr == -1) /* No vacant bit ? */
return -1;
orig_bit = AssignBit(bits, bit_nr, 1);
} while (orig_bit != 0); /* it got assigned before we tried */
return bit_nr;
}
#endif /* CONFIG_IPC */