/* $Header: malloc.c,v 1.0.1.1 88/01/24 03:53:23 root Exp $ * * $Log: malloc.c,v $ * Revision 1.0.1.1 88/01/24 03:53:23 root * patch 2: made depend on perl.h. * * Revision 1.0 87/12/18 13:05:35 root * Initial revision * */ #ifndef lint static char sccsid[] = "@(#)malloc.c 4.3 (Berkeley) 9/16/83"; #endif #include #define RCHECK /* * malloc.c (Caltech) 2/21/82 * Chris Kingsley, kingsley@cit-20. * * This is a very fast storage allocator. It allocates blocks of a small * number of different sizes, and keeps free lists of each size. Blocks that * don't exactly fit are passed up to the next larger size. In this * implementation, the available sizes are 2^n-4 (or 2^n-12) bytes long. * This is designed for use in a program that uses vast quantities of memory, * but bombs when it runs out. */ #include "EXTERN.h" #include "handy.h" #include "search.h" #include "perl.h" /* I don't much care whether these are defined in sys/types.h--LAW */ #define u_char unsigned char #define u_int unsigned int #define u_short unsigned short #define NULL 0 /* * The overhead on a block is at least 4 bytes. When free, this space * contains a pointer to the next free block, and the bottom two bits must * be zero. When in use, the first byte is set to MAGIC, and the second * byte is the size index. The remaining bytes are for alignment. * If range checking is enabled and the size of the block fits * in two bytes, then the top two bytes hold the size of the requested block * plus the range checking words, and the header word MINUS ONE. */ union overhead { union overhead *ov_next; /* when free */ struct { u_char ovu_magic; /* magic number */ u_char ovu_index; /* bucket # */ #ifdef RCHECK u_short ovu_size; /* actual block size */ u_int ovu_rmagic; /* range magic number */ #endif } ovu; #define ov_magic ovu.ovu_magic #define ov_index ovu.ovu_index #define ov_size ovu.ovu_size #define ov_rmagic ovu.ovu_rmagic }; #define MAGIC 0xff /* magic # on accounting info */ #define RMAGIC 0x55555555 /* magic # on range info */ #ifdef RCHECK #define RSLOP sizeof (u_int) #else #define RSLOP 0 #endif /* * nextf[i] is the pointer to the next free block of size 2^(i+3). The * smallest allocatable block is 8 bytes. The overhead information * precedes the data area returned to the user. */ #define NBUCKETS 30 static union overhead *nextf[NBUCKETS]; extern char *sbrk(); #ifdef MSTATS /* * nmalloc[i] is the difference between the number of mallocs and frees * for a given block size. */ static u_int nmalloc[NBUCKETS]; #include #endif #ifdef debug #define ASSERT(p) if (!(p)) botch("p"); else static botch(s) char *s; { printf("assertion botched: %s\n", s); abort(); } #else #define ASSERT(p) #endif char * malloc(nbytes) register unsigned nbytes; { register union overhead *p; register int bucket = 0; register unsigned shiftr; /* * Convert amount of memory requested into * closest block size stored in hash buckets * which satisfies request. Account for * space used per block for accounting. */ nbytes += sizeof (union overhead) + RSLOP; nbytes = (nbytes + 3) &~ 3; shiftr = (nbytes - 1) >> 2; /* apart from this loop, this is O(1) */ while (shiftr >>= 1) bucket++; /* * If nothing in hash bucket right now, * request more memory from the system. */ if (nextf[bucket] == NULL) morecore(bucket); if ((p = (union overhead *)nextf[bucket]) == NULL) return (NULL); /* remove from linked list */ if (*((int*)p) > 0x10000000) fprintf(stderr,"Corrupt malloc ptr 0x%x at 0x%x\n",*((int*)p),p); nextf[bucket] = nextf[bucket]->ov_next; p->ov_magic = MAGIC; p->ov_index= bucket; #ifdef MSTATS nmalloc[bucket]++; #endif #ifdef RCHECK /* * Record allocated size of block and * bound space with magic numbers. */ if (nbytes <= 0x10000) p->ov_size = nbytes - 1; p->ov_rmagic = RMAGIC; *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC; #endif return ((char *)(p + 1)); } /* * Allocate more memory to the indicated bucket. */ static morecore(bucket) register bucket; { register union overhead *op; register int rnu; /* 2^rnu bytes will be requested */ register int nblks; /* become nblks blocks of the desired size */ register int siz; if (nextf[bucket]) return; /* * Insure memory is allocated * on a page boundary. Should * make getpageize call? */ op = (union overhead *)sbrk(0); if ((int)op & 0x3ff) sbrk(1024 - ((int)op & 0x3ff)); /* take 2k unless the block is bigger than that */ rnu = (bucket <= 8) ? 11 : bucket + 3; nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */ if (rnu < bucket) rnu = bucket; op = (union overhead *)sbrk(1 << rnu); /* no more room! */ if ((int)op == -1) return; /* * Round up to minimum allocation size boundary * and deduct from block count to reflect. */ if ((int)op & 7) { op = (union overhead *)(((int)op + 8) &~ 7); nblks--; } /* * Add new memory allocated to that on * free list for this hash bucket. */ nextf[bucket] = op; siz = 1 << (bucket + 3); while (--nblks > 0) { op->ov_next = (union overhead *)((caddr_t)op + siz); op = (union overhead *)((caddr_t)op + siz); } } free(cp) char *cp; { register int size; register union overhead *op; if (cp == NULL) return; op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); #ifdef debug ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ #else if (op->ov_magic != MAGIC) return; /* sanity */ #endif #ifdef RCHECK ASSERT(op->ov_rmagic == RMAGIC); if (op->ov_index <= 13) ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC); #endif ASSERT(op->ov_index < NBUCKETS); size = op->ov_index; op->ov_next = nextf[size]; nextf[size] = op; #ifdef MSTATS nmalloc[size]--; #endif } /* * When a program attempts "storage compaction" as mentioned in the * old malloc man page, it realloc's an already freed block. Usually * this is the last block it freed; occasionally it might be farther * back. We have to search all the free lists for the block in order * to determine its bucket: 1st we make one pass thru the lists * checking only the first block in each; if that fails we search * ``realloc_srchlen'' blocks in each list for a match (the variable * is extern so the caller can modify it). If that fails we just copy * however many bytes was given to realloc() and hope it's not huge. */ int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */ char * realloc(cp, nbytes) char *cp; unsigned nbytes; { register u_int onb; union overhead *op; char *res; register int i; int was_alloced = 0; if (cp == NULL) return (malloc(nbytes)); op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); if (op->ov_magic == MAGIC) { was_alloced++; i = op->ov_index; } else { /* * Already free, doing "compaction". * * Search for the old block of memory on the * free list. First, check the most common * case (last element free'd), then (this failing) * the last ``realloc_srchlen'' items free'd. * If all lookups fail, then assume the size of * the memory block being realloc'd is the * smallest possible. */ if ((i = findbucket(op, 1)) < 0 && (i = findbucket(op, realloc_srchlen)) < 0) i = 0; } onb = (1 << (i + 3)) - sizeof (*op) - RSLOP; /* avoid the copy if same size block */ if (was_alloced && nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP) return(cp); if ((res = malloc(nbytes)) == NULL) return (NULL); if (cp != res) /* common optimization */ bcopy(cp, res, (nbytes < onb) ? nbytes : onb); if (was_alloced) free(cp); return (res); } /* * Search ``srchlen'' elements of each free list for a block whose * header starts at ``freep''. If srchlen is -1 search the whole list. * Return bucket number, or -1 if not found. */ static findbucket(freep, srchlen) union overhead *freep; int srchlen; { register union overhead *p; register int i, j; for (i = 0; i < NBUCKETS; i++) { j = 0; for (p = nextf[i]; p && j != srchlen; p = p->ov_next) { if (p == freep) return (i); j++; } } return (-1); } #ifdef MSTATS /* * mstats - print out statistics about malloc * * Prints two lines of numbers, one showing the length of the free list * for each size category, the second showing the number of mallocs - * frees for each size category. */ mstats(s) char *s; { register int i, j; register union overhead *p; int totfree = 0, totused = 0; fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s); for (i = 0; i < NBUCKETS; i++) { for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) ; fprintf(stderr, " %d", j); totfree += j * (1 << (i + 3)); } fprintf(stderr, "\nused:\t"); for (i = 0; i < NBUCKETS; i++) { fprintf(stderr, " %d", nmalloc[i]); totused += nmalloc[i] * (1 << (i + 3)); } fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n", totused, totfree); } #endif