Pearls5 编程小事

[TOC]

/* Copyright (C) 1999 Lucent Technologies */
/* From 'Programming Pearls' by Jon Bentley */

/* search.c -- test and time binary and sequential search
   Select one of three modes by editing main() below.
   1.) Probe one function
   2.) Test one function extensively
   3.) Time all functions
        Input lines:  algnum n numtests
        Output lines: algnum n numtests clicks nanosecs_per_elem
        See timedriver for algnum codes
 */

#include 
#include 
#include 

#define MAXN 1000000

typedef int DataType;

DataType x[MAXN];
int n;

/* Scaffolding */

int i = -999999;
#define assert(v) { if ((v) == 0) printf("  binarysearch bug %d %d\n", i, n); }

/* Alg 1: From Programming Pearls, Column 4: raw transliteration */

int binarysearch1(DataType t)
{   int l, u, m;
    l = 0;
    u = n-1;
    for (;;) {
        if (l > u)
            return -1;
        m = (l + u) / 2;
        if (x[m] < t)
            l = m+1;
        else if (x[m] == t)
            return m;
        else /* x[m] > t */
            u = m-1;
    }
}

/* Alg 2: Make binarysearch1 more c-ish */

int binarysearch2(DataType t)
{   int l, u, m;
    l = 0;
    u = n-1;
    while (l <= u) {
        m = (l + u) / 2;
        if (x[m] < t)
            l = m+1;
        else if (x[m] == t)
            return m;
        else /* x[m] > t */
            u = m-1;
    }
    return -1;
}

/* Alg 3: From PP, Col 8 */

int binarysearch3(DataType t)
{   int l, u, m;
    l = -1;
    u = n;
    while (l+1 != u) {
        m = (l + u) / 2;
        if (x[m] < t)
            l = m;
        else
            u = m;
    }
    if (u >= n || x[u] != t)
        return -1;
    return u;
}

/* Alg 4: From PP, Col 9 */

int binarysearch4(DataType t)
{   int l, p;
    if (n != 1000)
        return binarysearch3(t);
    l = -1;
    if (x[511]   < t) l = 1000 - 512;
    if (x[l+256] < t) l += 256;
    if (x[l+128] < t) l += 128;
    if (x[l+64 ] < t) l += 64;
    if (x[l+32 ] < t) l += 32;
    if (x[l+16 ] < t) l += 16;
    if (x[l+8  ] < t) l += 8;
    if (x[l+4  ] < t) l += 4;
    if (x[l+2  ] < t) l += 2;
    if (x[l+1  ] < t) l += 1;
    p = l+1;
    if (p >= n || x[p] != t)
        return -1;
    return p;
}

/* Alg 9: Buggy, from Programming Pearls, Column 5 */

int sorted()
{   int i;
    for (i = 0; i < n-1; i++)
        if (x[i] > x[i+1])
            return 0;
    return 1;
}

int binarysearch9(DataType t)
{   int l, u, m;
/* int oldsize, size = n+1; */
    l = 0;
    u = n-1;
    while (l <= u) {
/* oldsize = size;
size = u - l +1;
assert(size < oldsize); */
        m = (l + u) / 2;
/* printf("  %d %d %d\n", l, m, u); */
        if (x[m] < t)
            l = m;
        else if (x[m] > t)
            u = m;
        else {
            /* assert(x[m] == t); */
            return m;
        }
    }
    /* assert(x[l] > t && x[u] < t); */
    return -1;
}

/* Alg 21: Simple sequential search */

int seqsearch1(DataType t)
{   int i;
    for (i = 0; i < n; i++)
        if (x[i] == t)
            return i;
    return -1;
}

/* Alg 22: Faster sequential search: Sentinel */

int seqsearch2(DataType t)
{   int i;
    DataType hold = x[n];
    x[n] = t;
    for (i = 0; ; i++)
        if (x[i] == t)
            break;
    x[n] = hold;
    if (i == n)
        return -1;
    else
        return i;
}

/* Alg 23: Faster sequential search: loop unrolling */

int seqsearch3(DataType t)
{   int i;
    DataType hold = x[n];
    x[n] = t;
    for (i = 0; ; i+=8) {
        if (x[i] == t)   {          break; }
        if (x[i+1] == t) { i += 1; break; }
        if (x[i+2] == t) { i += 2; break; }
        if (x[i+3] == t) { i += 3; break; }
        if (x[i+4] == t) { i += 4; break; }
        if (x[i+5] == t) { i += 5; break; }
        if (x[i+6] == t) { i += 6; break; }
        if (x[i+7] == t) { i += 7; break; }
    }
    x[n] = hold;
    if (i == n)
        return -1;
    else
        return i;
}


/* Scaffolding to probe one algorithm */

void probe1()
{   int i;
    DataType t;
    while (scanf("%d %d", &n, &t) != EOF) {
        for (i = 0; i < n; i++)
            x[i] = 10*i;
        printf(" %d\n", binarysearch9(t));
    }
}


/* Torture test one algorithm */

#define s seqsearch3
void test(int maxn)
{   int i;
    for (n = 0; n <= maxn; n++) {
        printf("n=%d\n", n);
        /* distinct elements (plus one at top) */
        for (i = 0; i <= n; i++)
            x[i] = 10*i;
        for (i = 0; i < n; i++) {
            assert(s(10*i)     ==  i);
            assert(s(10*i - 5) == -1);
        }
        assert(s(10*n - 5) == -1);
        assert(s(10*n)     == -1);
        /* equal elements */
        for (i = 0; i < n; i++)
            x[i] = 10;
        if (n == 0) {
            assert(s(10) == -1);
        } else {
            assert(0 <= s(10) && s(10) < n);
        }
        assert(s(5) == -1);
        assert(s(15) == -1);
    }
}

/* Timing */

int p[MAXN];

void scramble(int n)
{   int i, j;
    DataType t;
    for (i = n-1; i > 0; i--) {
        j = (RAND_MAX*rand() + rand()) % (i + 1);
        t = p[i]; p[i] = p[j]; p[j] = t;
    }
}

void timedriver()
{   int i, algnum, numtests, test, start, clicks;
    while (scanf("%d %d %d", &algnum, &n, &numtests) != EOF) {
        for (i = 0; i < n; i++)
            x[i] = i;
        for (i = 0; i < n; i++)
            p[i] = i;
        scramble(n);
        start = clock();
        for (test = 0; test < numtests; test++) {
            for (i = 0; i < n; i++) {
                switch (algnum) {
                case 1:  assert(binarysearch1(p[i]) == p[i]); break;
                case 2:  assert(binarysearch2(p[i]) == p[i]); break;
                case 3:  assert(binarysearch3(p[i]) == p[i]); break;
                case 4:  assert(binarysearch4(p[i]) == p[i]); break;
                case 9:  assert(binarysearch9(p[i]) == p[i]); break;
                case 21: assert(seqsearch1(p[i]) == p[i]); break;
                case 22: assert(seqsearch2(p[i]) == p[i]); break;
                case 23: assert(seqsearch3(p[i]) == p[i]); break;
                }
            }
        }
        clicks = clock() - start;
        printf("%d\t%d\t%d\t%d\t%g\n",
            algnum, n, numtests, clicks,
            1e9*clicks/((float) CLOCKS_PER_SEC*n*numtests));
    }
}

/* Main */

int main()
{   /* probe1(); */
    /* test(25); */
    timedriver();
    return 0;
}