[SOLVED] CS /* Generates about 1 MB of random data that is then divided into

/* Generates about 1 MB of random data that is then divided into
16 chunks.A separate subprocess sorts each chunk; the
subprocesses run in parallel.Then we merge the chunks and
verify that the result is what it should be. */

#include tests/vm/parallel-merge.h
#include
#include
#include tests/arc4.h
#include tests/lib.h
#include tests/main.h

#define CHUNK_SIZE (128 * 1024)
#define CHUNK_CNT 8 /* Number of chunks. */
#define DATA_SIZE (CHUNK_CNT * CHUNK_SIZE)/* Buffer size. */

unsigned char buf1[DATA_SIZE], buf2[DATA_SIZE];
size_t histogram[256];

/* Initialize buf1 with random data,
then count the number of instances of each value within it. */
static void
init (void)
{
struct arc4 arc4;
size_t i;

msg (init);

arc4_init (&arc4, foobar, 6);
arc4_crypt (&arc4, buf1, sizeof buf1);
for (i = 0; i < sizeof buf1; i++)histogram[buf1[i]]++;}/* Sort each chunk of buf1 using SUBPROCESS, which is expected to return EXIT_STATUS. */static voidsort_chunks (const char *subprocess, int exit_status){pid_t children[CHUNK_CNT];size_t i;for (i = 0; i < CHUNK_CNT; i++) {char fn[128];char cmd[128];int handle;msg (“sort chunk %zu”, i);/* Write this chunk to a file. */snprintf (fn, sizeof fn, “buf%zu”, i);create (fn, CHUNK_SIZE);quiet = true;CHECK ((handle = open (fn)) > 1, open %s, fn);
write (handle, buf1 + CHUNK_SIZE * i, CHUNK_SIZE);
close (handle);

/* Sort with subprocess. */
snprintf (cmd, sizeof cmd, %s %s, subprocess, fn);
CHECK ((children[i] = exec (cmd)) != -1, exec %s, cmd);
quiet = false;
}

for (i = 0; i < CHUNK_CNT; i++) {char fn[128];int handle;CHECK (wait (children[i]) == exit_status, “wait for child %zu”, i);/* Read chunk back from file. */quiet = true;snprintf (fn, sizeof fn, “buf%zu”, i);CHECK ((handle = open (fn)) > 1, open %s, fn);
read (handle, buf1 + CHUNK_SIZE * i, CHUNK_SIZE);
close (handle);
quiet = false;
}
}

/* Merge the sorted chunks in buf1 into a fully sorted buf2. */
static void
merge (void)
{
unsigned char *mp[CHUNK_CNT];
size_t mp_left;
unsigned char *op;
size_t i;

msg (merge);

/* Initialize merge pointers. */
mp_left = CHUNK_CNT;
for (i = 0; i < CHUNK_CNT; i++)mp[i] = buf1 + CHUNK_SIZE * i;/* Merge. */op = buf2;while (mp_left > 0)
{
/* Find smallest value. */
size_t min = 0;
for (i = 1; i < mp_left; i++)if (*mp[i] < *mp[min])min = i;/* Append value to buf2. */*op++ = *mp[min];/* Advance merge pointer. Delete this chunk from the set if it’s emptied. */if ((++mp[min] – buf1) % CHUNK_SIZE == 0) mp[min] = mp[–mp_left];}}static voidverify (void) {size_t buf_idx;size_t hist_idx;msg (“verify”);buf_idx = 0;for (hist_idx = 0; hist_idx < sizeof histogram / sizeof *histogram; hist_idx++){while (histogram[hist_idx]– > 0)
{
if (buf2[buf_idx] != hist_idx)
fail (bad value %d in byte %zu, buf2[buf_idx], buf_idx);
buf_idx++;
}
}

msg (success, buf_idx=%zu, buf_idx);
}

void
parallel_merge (const char *child_name, int exit_status)
{
init ();
sort_chunks (child_name, exit_status);
merge ();
verify ();
}