/*
* File: alloc.c
* Purpose: generic malloc() and free() engine
*
* Notes: 99% of this code stolen/borrowed from the K&R C
* examples.
*
*/
#include "common.h"
#include "stdlib.h"
#pragma section = "HEAP"
/********************************************************************/
/*
* This struct forms the minimum block size which is allocated, and
* also forms the linked list for the memory space used with alloc()
* and free(). It is padded so that on a 32-bit machine, all malloc'ed
* pointers are 16-byte aligned.
*/
typedef struct ALLOC_HDR
{
struct
{
struct ALLOC_HDR *
ptr;
unsigned int size;
} s;
unsigned int align;
unsigned int pad;
} ALLOC_HDR;
static ALLOC_HDR
base;
static ALLOC_HDR *freep =
NULL;
/********************************************************************/
void free(
void *
ap )
{
ALLOC_HDR *bp, *
p;
bp = (ALLOC_HDR *) ap -
1;
/* point to block header */
for ( p = freep; !( ( bp > p ) && ( bp < p->s.ptr ) ); p = p->
s.ptr )
{
if ( ( p >= p->s.ptr ) && ( ( bp > p ) || ( bp < p->
s.ptr ) ) )
{
break;
/* freed block at start or end of arena */
}
}
if ( ( bp + bp->s.size ) == p->
s.ptr )
{
bp->s.size += p->s.ptr->
s.size;
bp->s.ptr = p->s.ptr->
s.ptr;
}
else
{
bp->s.ptr = p->
s.ptr;
}
if ( ( p + p->s.size ) ==
bp )
{
p->s.size += bp->
s.size;
p->s.ptr = bp->
s.ptr;
}
else
{
p->s.ptr =
bp;
}
freep =
p;
}
/********************************************************************/
void *
malloc( unsigned nbytes )
{
/* Get addresses for the HEAP start and end */
char* __HEAP_START = __section_begin(
"HEAP");
char* __HEAP_END = __section_end(
"HEAP");
ALLOC_HDR *p, *
prevp;
unsigned nunits;
nunits = ( ( nbytes +
sizeof(ALLOC_HDR) -
1 ) /
sizeof(ALLOC_HDR) ) +
1;
if ( ( prevp = freep ) ==
NULL )
{
p = (ALLOC_HDR *
) __HEAP_START;
p->s.size = ( ( (uint32) __HEAP_END -
(uint32) __HEAP_START )
/
sizeof(ALLOC_HDR) );
p->s.ptr = &
base;
base.s.ptr =
p;
base.s.size =
0;
prevp = freep = &
base;
}
for ( p = prevp->s.ptr;; prevp = p, p = p->
s.ptr )
{
if ( p->s.size >=
nunits )
{
if ( p->s.size ==
nunits )
{
prevp->s.ptr = p->
s.ptr;
}
else
{
p->s.size -=
nunits;
p += p->
s.size;
p->s.size =
nunits;
}
freep =
prevp;
return (
void *) ( p +
1 );
}
if ( p ==
freep )
return NULL;
}
}
/********************************************************************/
转载于:https://www.cnblogs.com/shangdawei/archive/2013/04/22/3036831.html
相关资源：C语言实现malloc和free
