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/*
Homework n.3
Usando la possibilita' di mappare file in memoria, creare un programma che
possa manipolare un file arbitrariamente grande costituito da una sequenza
di record lunghi N byte.
La manipolazione consiste nel riordinare, tramite un algoritmo di ordinamento
a scelta, i record considerando il contenuto dello stesso come chiave:
ovvero, supponendo N=5, il record [4a a4 91 f0 01] precede [4a ff 10 01 a3].
La sintassi da supportare e' la seguente:
$ homework-3
E' possibile testare il programma sul file 'esempio.txt' prodotto dal seguente
comando, utilizzando il parametro N=33:
$ ( for I in `seq 1000`; do echo $I | md5sum | cut -d' ' -f1 ; done ) > esempio.txt
Su tale file, l'output atteso e' il seguente:
$ homework-3 33 esempio.txt
$ head -n5 esempio.txt
000b64c5d808b7ae98718d6a191325b7
0116a06b764c420b8464f2068f2441c8
015b269d0f41db606bd2c724fb66545a
01b2f7c1a89cfe5fe8c89fa0771f0fde
01cdb6561bfb2fa34e4f870c90589125
$ tail -n5 esempio.txt
ff7345a22bc3605271ba122677d31cae
ff7f2c85af133d62c53b36a83edf0fd5
ffbee273c7bb76bb2d279aa9f36a43c5
ffbfc1313c9c855a32f98d7c4374aabd
ffd7e3b3836978b43da5378055843c67
*/
#include
#include
#include
#include
#include
#include
#include
#include
char *swap_buffer; // riferimento ad buffer di scambio globale
/* trova il pivot in map[i]...map[j] restituendone una copia (allocando la memoria);
restituisce NULL se gli elementi sono tutti uguali */
char *search_pivot(char *map, int i, int j, int size) {
int k;
for (k=i+1; k<=j; k++) {
if (memcmp(map+size*k, map+size*i, size) > 0) // map[k] > map[i]
return(memcpy(malloc(size), map+size*k, size)); // pivot = map[k]
else if (memcmp(map+size*k, map+size*i, size) < 0) // map[k] < map[i]
return(memcpy(malloc(size), map+size*i, size)); // pivot = map[i]
}
return(NULL);
}
// partiziona map[p]...map[r] usando il pivot
int partition(char *map, int p, int r, char *pivot, int size) {
int i, j;
i = p;
j = r;
do {
while (memcmp(map+size*j, pivot, size) >= 0) // map[j] >= pivot
j--;
while (memcmp(map+size*i, pivot, size) < 0) // map[i] < pivot
i++;
if (i map[j]
memcpy(swap_buffer, map+size*i, size);
memcpy(map+size*i, map+size*j, size);
memcpy(map+size*j, swap_buffer, size);
}
} while (i \n", argv[0]);
exit(1);
}
if ((fd = open(argv[2], O_RDWR)) == -1) {
perror(argv[2]);
exit(1);
}
if (fstat(fd, &sb) == -1) {
perror("fstat");
exit(1);
}
if (!S_ISREG(sb.st_mode)) {
fprintf(stderr, "%s non รจ un file\n", argv[2]);
exit(1);
}
size = atoi(argv[1]);
if ( (size <= 0) || ((sb.st_size % size) != 0) ) {
fprintf(stderr, "dimensione del record %d non valida o dimensione del file non congruente!\n", size);
exit(1);
}
if ((map = mmap(NULL, sb.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED) {
perror("mmap");
exit(1);
}
if (close(fd) == -1) {
perror ("close");
exit(1);
}
// alloca il buffer di scambio globale (al posto di uno locale alla procedura 'partition'
swap_buffer = malloc(size);
// ordina il contenuto del file
num_records = sb.st_size / size;
quicksort(map, 0, num_records-1, size);
// libera la memoria del buffer una volta finito
free(swap_buffer);
printf("Record del file '%s' riordinati!\n", argv[2]);
if (munmap(map, sb.st_size) == -1) {
perror ("munmap");
exit(1);
}
}