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Заключение
Внешняя сортировка методом поглощения позволяет сэкономить время и при не большом размере файла сортировка проходит быстро.
Реализация метода на C
/* external sort */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/****************************
* implementation dependent *
****************************/
/* template for workfiles (8.3 format) */
#define FNAME "_sort%03d.dat"
#define LNAME 13
/* comparison operators */
#define compLT(x,y) (x < y)
#define compGT(x,y) (x > y)
/* define the record to be sorted here */
#define LRECL 100
typedef int keyType;
typedef struct recTypeTag {
keyType key; /* sort key for record */
#if LRECL
char data[LRECL-sizeof(keyType)]; /* other fields */
#endif
} recType;
/******************************
* implementation independent *
******************************/
typedef enum {false, true} bool;
typedef struct tmpFileTag {
FILE *fp; /* file pointer */
char name[LNAME]; /* filename */
recType rec; /* last record read */
int dummy; /* number of dummy runs */
bool eof; /* end-of-file flag */
bool eor; /* end-of-run flag */
bool valid; /* true if rec is valid */
int fib; /* ideal fibonacci number */
} tmpFileType;
static tmpFileType **file; /* array of file info for tmp files */
static int nTmpFiles; /* number of tmp files */
static char *ifName; /* input filename */
static char *ofName; /* output filename */
static int level; /* level of runs */
static int nNodes; /* number of nodes for selection tree */
void deleteTmpFiles(void) {
int i;
/* delete merge files and free resources */
if (file) {
for (i = 0; i < nTmpFiles; i++) {
if (file[i]) {
if (file[i]->fp) fclose(file[i]->fp);
if (*file[i]->name) remove(file[i]->name);
free (file[i]);
}
}
free (file);
}
}
void termTmpFiles(int rc) {
/* cleanup files */
remove(ofName);
if (rc == 0) {
int fileT;
/* file[T] contains results */
fileT = nTmpFiles - 1;
fclose(file[fileT]->fp); file[fileT]->fp = NULL;
if (rename(file[fileT]->name, ofName)) {
perror("io1");
deleteTmpFiles();
exit(1);
}
*file[fileT]->name = 0;
}
deleteTmpFiles();
}
void cleanExit(int rc) {
/* cleanup tmp files and exit */
termTmpFiles(rc);
exit(rc);
}
void *safeMalloc(size_t size) {
void *p;
/* safely allocate memory and initialize to zero */
if ((p = calloc(1, size)) == NULL) {
printf("error: malloc failed, size = %d\n", size);
cleanExit(1);
}
return p;
}
void initTmpFiles(void) {
int i;
tmpFileType *fileInfo;
/* initialize merge files */
if (nTmpFiles < 3) nTmpFiles = 3;
file = safeMalloc(nTmpFiles * sizeof(tmpFileType*));
fileInfo = safeMalloc(nTmpFiles * sizeof(tmpFileType));
for (i = 0; i < nTmpFiles; i++) {
file[i] = fileInfo + i;
sprintf(file[i]->name, FNAME, i);
if ((file[i]->fp = fopen(file[i]->name, "w+b")) == NULL) {
perror("io2");
cleanExit(1);
}
}
}
recType *readRec(void) {
typedef struct iNodeTag { /* internal node */
struct iNodeTag *parent;/* parent of internal node */
struct eNodeTag *loser; /* external loser */
} iNodeType;
typedef struct eNodeTag { /* external node */
struct iNodeTag *parent;/* parent of external node */
recType rec; /* input record */
int run; /* run number */
bool valid; /* input record is valid */
} eNodeType;
typedef struct nodeTag {
iNodeType i; /* internal node */
eNodeType e; /* external node */
} nodeType;
static nodeType *node; /* array of selection tree nodes */
static eNodeType *win; /* new winner */
static FILE *ifp; /* input file */
static bool eof; /* true if end-of-file, input */
static int maxRun; /* maximum run number */
static int curRun; /* current run number */
iNodeType *p; /* pointer to internal nodes */
static bool lastKeyValid; /* true if lastKey is valid */
static keyType lastKey; /* last key written */
/* read next record using replacement selection */
/* check for first call */
if (node == NULL) {
int i;
if (nNodes < 2) nNodes = 2;
node = safeMalloc(nNodes * sizeof(nodeType));
for (i = 0; i < nNodes; i++) {
node[i].i.loser = &node[i].e;
node[i].i.parent = &node[i/2].i;
node[i].e.parent = &node[(nNodes + i)/2].i;
node[i].e.run = 0;
node[i].e.valid = false;
}
win = &node[0].e;
lastKeyValid = false;
if ((ifp = fopen(ifName, "rb")) == NULL) {
printf("error: file %s, unable to open\n", ifName);
cleanExit(1);
}
}
while (1) {
/* replace previous winner with new record */
if (!eof) {
if (fread(&win->rec, sizeof(recType), 1, ifp) == 1) {
if ((!lastKeyValid || compLT(win->rec.key, lastKey))
&& (++win->run > maxRun))
maxRun = win->run;
win->valid = true;
} else if (feof(ifp)) {
fclose(ifp);
eof = true;
win->valid = false;
win->run = maxRun + 1;
} else {
perror("io4");
cleanExit(1);
}
} else {
win->valid = false;
win->run = maxRun + 1;
}
/* adjust loser and winner pointers */
p = win->parent;
do {
bool swap;
swap = false;
if (p->loser->run < win->run) {
swap = true;
} else if (p->loser->run == win->run) {
if (p->loser->valid && win->valid) {
if (compLT(p->loser->rec.key, win->rec.key))
swap = true;
} else {
swap = true;
}
}
if (swap) {
/* p should be winner */
eNodeType *t;
t = p->loser;
p->loser = win;
win = t;
}
p = p->parent;
} while (p!= &node[0].i);
/* end of run? */
if (win->run!= curRun) {
/* win->run = curRun + 1 */
if (win->run > maxRun) {
/* end of output */
free(node);
return NULL;
}
curRun = win->run;
}
/* output top of tree */
if (win->run) {
lastKey = win->rec.key;
lastKeyValid = true;
return &win->rec;
}
}
}
void makeRuns(void) {
recType *win; /* winner */
int fileT; /* last file */
int fileP; /* next to last file */
int j; /* selects file[j] */
/* Make initial runs using replacement selection.
* Runs are written using a Fibonacci distintbution.
*/
/* initialize file structures */
fileT = nTmpFiles - 1;
fileP = fileT - 1;
for (j = 0; j < fileT; j++) {
file[j]->fib = 1;
file[j]->dummy = 1;
}
file[fileT]->fib = 0;
file[fileT]->dummy = 0;
level = 1;
j = 0;
win = readRec();
while (win) {
bool anyrun;
anyrun = false;
for (j = 0; win && j <= fileP; j++) {
bool run;
run = false;
if (file[j]->valid) {
if (!compLT(win->key, file[j]->rec.key)) {
/* append to an existing run */
run = true;
} else if (file[j]->dummy) {
/* start a new run */
file[j]->dummy--;
run = true;
}
} else {
/* first run in file */
file[j]->dummy--;
run = true;
}
if (run) {
anyrun = true;
/* flush run */
while(1) {
if (fwrite(win, sizeof(recType), 1, file[j]->fp)!= 1) {
perror("io3");
cleanExit(1);
}
file[j]->rec.key = win->key;
file[j]->valid = true;
if ((win = readRec()) == NULL) break;
if (compLT(win->key, file[j]->rec.key)) break;
}
}
}
/* if no room for runs, up a level */
if (!anyrun) {
int t;
level++;
t = file[0]->fib;
for (j = 0; j <= fileP; j++) {
file[j]->dummy = t + file[j+1]->fib - file[j]->fib;
file[j]->fib = t + file[j+1]->fib;
}
}
}
}
void rewindFile(int j) {
/* rewind file[j] and read in first record */
file[j]->eor = false;
file[j]->eof = false;
rewind(file[j]->fp);
if (fread(&file[j]->rec, sizeof(recType), 1, file[j]->fp)!= 1) {
if (feof(file[j]->fp)) {
file[j]->eor = true;
file[j]->eof = true;
} else {
perror("io5");
cleanExit(1);
}
}
}
void mergeSort(void) {
int fileT;
int fileP;
int j;
tmpFileType *tfile;
/* polyphase merge sort */
fileT = nTmpFiles - 1;
fileP = fileT - 1;
/* prime the files */
for (j = 0; j < fileT; j++) {
rewindFile(j);
}
/* each pass through loop merges one run */
while (level) {
while(1) {
bool allDummies;
bool anyRuns;
/* scan for runs */
allDummies = true;
anyRuns = false;
for (j = 0; j <= fileP; j++) {
if (!file[j]->dummy) {
allDummies = false;
if (!file[j]->eof) anyRuns = true;
}
}
if (anyRuns) {
int k;
keyType lastKey;
/* merge 1 run file[0]..file[P] --> file[T] */
while(1) {
/* each pass thru loop writes 1 record to file[fileT] */
/* find smallest key */
k = -1;
for (j = 0; j <= fileP; j++) {
if (file[j]->eor) continue;
if (file[j]->dummy) continue;
if (k < 0 ||
(k!= j && compGT(file[k]->rec.key, file[j]->rec.key)))
k = j;
}
if (k < 0) break;
/* write record[k] to file[fileT] */
if (fwrite(&file[k]->rec, sizeof(recType), 1,
file[fileT]->fp)!= 1) {
perror("io6");
cleanExit(1);
}
/* replace record[k] */
lastKey = file[k]->rec.key;
if (fread(&file[k]->rec, sizeof(recType), 1,
file[k]->fp) == 1) {
/* check for end of run on file[s] */
if (compLT(file[k]->rec.key, lastKey))
file[k]->eor = true;
} else if (feof(file[k]->fp)) {
file[k]->eof = true;
file[k]->eor = true;
} else {
perror("io7");
cleanExit(1);
}
}
/* fixup dummies */
for (j = 0; j <= fileP; j++) {
if (file[j]->dummy) file[j]->dummy--;
if (!file[j]->eof) file[j]->eor = false;
}
} else if (allDummies) {
for (j = 0; j <= fileP; j++)
file[j]->dummy--;
file[fileT]->dummy++;
}
/* end of run */
if (file[fileP]->eof &&!file[fileP]->dummy) {
/* completed a fibonocci-level */
level--;
if (!level) {
/* we're done, file[fileT] contains data */
return;
}
/* fileP is exhausted, reopen as new */
fclose(file[fileP]->fp);
if ((file[fileP]->fp = fopen(file[fileP]->name, "w+b"))
== NULL) {
perror("io8");
cleanExit(1);
}
file[fileP]->eof = false;
file[fileP]->eor = false;
rewindFile(fileT);
/* f[0],f[1]...,f[fileT] <-- f[fileT],f[0]...,f[T-1] */
tfile = file[fileT];
memmove(file + 1, file, fileT * sizeof(tmpFileType*));
file[0] = tfile;
/* start new runs */
for (j = 0; j <= fileP; j++)
if (!file[j]->eof) file[j]->eor = false;
}
}
}
}
void extSort(void) {
initTmpFiles();
makeRuns();
mergeSort();
termTmpFiles(0);
}
int main(int argc, char *argv[]) {
/* command-line:
*
* ext ifName ofName nTmpFiles nNodes
*
* ext in.dat out.dat 5 2000
* reads in.dat, sorts using 5 files and 2000 nodes, output to out.dat
*/
if (argc!= 5) {
printf("%s ifName ofName nTmpFiles nNodes\n", argv[0]);
cleanExit(1);
}
ifName = argv[1];
ofName = argv[2];
nTmpFiles = atoi(argv[3]);
nNodes = atoi(argv[4]);
printf("extSort: nFiles=%d, nNodes=%d, lrecl=%d\n",
nTmpFiles, nNodes, sizeof(recType));
extSort();
return 0;
}
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