usr/src/usr.bin/look/look.c

/*-
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * David Hitz of Auspex Systems, Inc.
 *
 * %sccs.include.redist.c%
 */

#ifndef lint
static char copyright[] =
"@(#) Copyright (c) 1991, 1993\n\
        The Regents of the University of California.  All rights reserved.\n";
#endif /* not lint */

#ifndef lint
static char sccsid[] = "@(#)look.c      8.1 (Berkeley) %G%";
#endif /* not lint */

/*
 * look -- find lines in a sorted list.
 *
 * The man page said that TABs and SPACEs participate in -d comparisons.
 * In fact, they were ignored.  This implements historic practice, not
 * the manual page.
 */

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>

#include <limits.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "pathnames.h"

/*
 * FOLD and DICT convert characters to a normal form for comparison,
 * according to the user specified flags.
 *
 * DICT expects integers because it uses a non-character value to
 * indicate a character which should not participate in comparisons.
 */
#define EQUAL           0
#define GREATER         1
#define LESS            (-1)
#define NO_COMPARE      (-2)

#define FOLD(c) (isascii(c) && isupper(c) ? tolower(c) : (c))
#define DICT(c) (isascii(c) && isalnum(c) ? (c) : NO_COMPARE)

int dflag, fflag;

char    *binary_search __P((char *, char *, char *));
int      compare __P((char *, char *, char *));
void     err __P((const char *fmt, ...));
char    *linear_search __P((char *, char *, char *));
int      look __P((char *, char *, char *));
void     print_from __P((char *, char *, char *));

static void usage __P((void));

main(argc, argv)
        int argc;
        char *argv[];
{
        struct stat sb;
        int ch, fd, termchar;
        char *back, *file, *front, *string, *p;

        file = _PATH_WORDS;
        termchar = '\0';
        while ((ch = getopt(argc, argv, "dft:")) != EOF)
                switch(ch) {
                case 'd':
                        dflag = 1;
                        break;
                case 'f':
                        fflag = 1;
                        break;
                case 't':
                        termchar = *optarg;
                        break;
                case '?':
                default:
                        usage();
                }
        argc -= optind;
        argv += optind;

        switch (argc) {
        case 2:                         /* Don't set -df for user. */
                string = *argv++;
                file = *argv;
                break;
        case 1:                         /* But set -df by default. */
                dflag = fflag = 1;
                string = *argv;
                break;
        default:
                usage();
        }

        if (termchar != '\0' && (p = strchr(string, termchar)) != NULL)
                *++p = '\0';

        if ((fd = open(file, O_RDONLY, 0)) < 0 || fstat(fd, &sb))
                err("%s: %s", file, strerror(errno));
        if (sb.st_size > SIZE_T_MAX)
                err("%s: %s", file, strerror(EFBIG));
        if ((front = mmap(NULL,
            (size_t)sb.st_size, PROT_READ, 0, fd, (off_t)0)) == NULL)
                err("%s: %s", file, strerror(errno));
        back = front + sb.st_size;
        exit(look(string, front, back));
}

look(string, front, back)
        char *string, *front, *back;
{
        register int ch;
        register char *readp, *writep;

        /* Reformat string string to avoid doing it multiple times later. */
        for (readp = writep = string; ch = *readp++;) {
                if (fflag)
                        ch = FOLD(ch);
                if (dflag)
                        ch = DICT(ch);
                if (ch != NO_COMPARE)
                        *(writep++) = ch;
        }
        *writep = '\0';

        front = binary_search(string, front, back);
        front = linear_search(string, front, back);

        if (front)
                print_from(string, front, back);
        return (front ? 0 : 1);
}


/*
 * Binary search for "string" in memory between "front" and "back".
 *
 * This routine is expected to return a pointer to the start of a line at
 * *or before* the first word matching "string".  Relaxing the constraint
 * this way simplifies the algorithm.
 *
 * Invariants:
 *      front points to the beginning of a line at or before the first
 *      matching string.
 *
 *      back points to the beginning of a line at or after the first
 *      matching line.
 *
 * Base of the Invariants.
 *      front = NULL;
 *      back = EOF;
 *
 * Advancing the Invariants:
 *
 *      p = first newline after halfway point from front to back.
 *
 *      If the string at "p" is not greater than the string to match,
 *      p is the new front.  Otherwise it is the new back.
 *
 * Termination:
 *
 *      The definition of the routine allows it return at any point,
 *      since front is always at or before the line to print.
 *
 *      In fact, it returns when the chosen "p" equals "back".  This
 *      implies that there exists a string is least half as long as
 *      (back - front), which in turn implies that a linear search will
 *      be no more expensive than the cost of simply printing a string or two.
 *
 *      Trying to continue with binary search at this point would be
 *      more trouble than it's worth.
 */
#define SKIP_PAST_NEWLINE(p, back) \
        while (p < back && *p++ != '\n');

char *
binary_search(string, front, back)
        register char *string, *front, *back;
{
        register char *p;

        p = front + (back - front) / 2;
        SKIP_PAST_NEWLINE(p, back);

        /*
         * If the file changes underneath us, make sure we don't
         * infinitely loop.
         */
        while (p < back && back > front) {
                if (compare(string, p, back) == GREATER)
                        front = p;
                else
                        back = p;
                p = front + (back - front) / 2;
                SKIP_PAST_NEWLINE(p, back);
        }
        return (front);
}

/*
 * Find the first line that starts with string, linearly searching from front
 * to back.
 *
 * Return NULL for no such line.
 *
 * This routine assumes:
 *
 *      o front points at the first character in a line.
 *      o front is before or at the first line to be printed.
 */
char *
linear_search(string, front, back)
        char *string, *front, *back;
{
        while (front < back) {
                switch (compare(string, front, back)) {
                case EQUAL:             /* Found it. */
                        return (front);
                        break;
                case LESS:              /* No such string. */
                        return (NULL);
                        break;
                case GREATER:           /* Keep going. */
                        break;
                }
                SKIP_PAST_NEWLINE(front, back);
        }
        return (NULL);
}

/*
 * Print as many lines as match string, starting at front.
 */
void
print_from(string, front, back)
        register char *string, *front, *back;
{
        for (; front < back && compare(string, front, back) == EQUAL; ++front) {
                for (; front < back && *front != '\n'; ++front)
                        if (putchar(*front) == EOF)
                                err("stdout: %s", strerror(errno));
                if (putchar('\n') == EOF)
                        err("stdout: %s", strerror(errno));
        }
}

/*
 * Return LESS, GREATER, or EQUAL depending on how the string1 compares with
 * string2 (s1 ??? s2).
 *
 *      o Matches up to len(s1) are EQUAL.
 *      o Matches up to len(s2) are GREATER.
 *
 * Compare understands about the -f and -d flags, and treats comparisons
 * appropriately.
 *
 * The string "s1" is null terminated.  The string s2 is '\n' terminated (or
 * "back" terminated).
 */
int
compare(s1, s2, back)
        register char *s1, *s2, *back;
{
        register int ch;

        for (; *s1 && s2 < back && *s2 != '\n'; ++s1, ++s2) {
                ch = *s2;
                if (fflag)
                        ch = FOLD(ch);
                if (dflag)
                        ch = DICT(ch);

                if (ch == NO_COMPARE) {
                        ++s2;           /* Ignore character in comparison. */
                        continue;
                }
                if (*s1 != ch)
                        return (*s1 < ch ? LESS : GREATER);
        }
        return (*s1 ? GREATER : EQUAL);
}

static void
usage()
{
        (void)fprintf(stderr, "usage: look [-df] [-t char] string [file]\n");
        exit(2);
}

#if __STDC__
#include <stdarg.h>
#else
#include <varargs.h>
#endif

void
#if __STDC__
err(const char *fmt, ...)
#else
err(fmt, va_alist)
        char *fmt;
        va_dcl
#endif
{
        va_list ap;
#if __STDC__
        va_start(ap, fmt);
#else
        va_start(ap);
#endif
        (void)fprintf(stderr, "look: ");
        (void)vfprintf(stderr, fmt, ap);
        va_end(ap);
        (void)fprintf(stderr, "\n");
        exit(2);
        /* NOTREACHED */
}