90 lines
1.6 KiB
C
90 lines
1.6 KiB
C
#include "types.h"
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#include "stat.h"
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#include "user.h"
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#include "param.h"
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// Memory allocator by Kernighan and Ritchie, The C programming Language,
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// 2nd ed. Section 8.7.
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typedef long Align;
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union header {
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struct {
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union header *ptr;
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uint size;
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} s;
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Align x;
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};
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typedef union header Header;
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static Header base;
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static Header *freep = 0;
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void
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free(void *ap)
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{
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Header *bp, *p;
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bp = (Header*) ap - 1;
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for(p = freep; !(bp > p && bp < p->s.ptr); p = p->s.ptr)
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if(p >= p->s.ptr && (bp > p || bp < p->s.ptr))
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break;
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if(bp + bp->s.size == p->s.ptr) {
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bp->s.size += p->s.ptr->s.size;
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bp->s.ptr = p->s.ptr->s.ptr;
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} else
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bp->s.ptr = p->s.ptr;
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if(p + p->s.size == bp) {
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p->s.size += bp->s.size;
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p->s.ptr = bp->s.ptr;
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} else
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p->s.ptr = bp;
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freep = p;
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}
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static Header*
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morecore(uint nu)
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{
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char *p;
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Header *hp;
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if(nu < PAGE)
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nu = PAGE;
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p = sbrk(nu * sizeof(Header));
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if(p == (char*) -1)
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return 0;
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hp = (Header*)p;
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hp->s.size = nu;
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free((void*)(hp + 1));
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return freep;
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}
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void*
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malloc(uint nbytes)
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{
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Header *p, *prevp;
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uint nunits;
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nunits = (nbytes + sizeof(Header) - 1)/sizeof(Header) + 1;
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if((prevp = freep) == 0) {
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base.s.ptr = freep = prevp = &base;
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base.s.size = 0;
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}
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for(p = prevp->s.ptr; ; prevp = p, p = p->s.ptr) {
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if(p->s.size >= nunits) {
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if(p->s.size == nunits)
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prevp->s.ptr = p->s.ptr;
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else {
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p->s.size -= nunits;
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p += p->s.size;
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p->s.size = nunits;
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}
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freep = prevp;
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return (void*) (p + 1);
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}
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if(p == freep)
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if((p = morecore(nunits)) == 0)
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return 0;
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}
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}
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