util.c

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#include <string.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <errno.h>
#include "util.h"

/* This file contains utility functions widely used in *
 * my programs.  Many are simply versions of file and  *
 * memory grabbing routines that take the same         *
 * arguments as the standard library ones, but exit    *
 * the program if they find an error condition.        */

int file_line_number; /* file in line number being parsed */
char *out_file_prefix = NULL;
messagelogger vpr_printf = PrintHandlerMessage;

static int cont; /* line continued? */

/* Returns the min of cur and max. If cur > max, a warning
 * is emitted. */
int limit_value(int cur, int max, const char *name) {
    if (cur > max) {
        vpr_printf(TIO_MESSAGE_WARNING,
                "%s is being limited from [%d] to [%d]\n", name, cur, max);
        return max;
    }
    return cur;
}

/* An alternate for strncpy since strncpy doesn't work as most
 * people would expect. This ensures null termination */
char *
my_strncpy(char *dest, const char *src, size_t size) {
    /* Find string's length */
    size_t len = strlen(src);

    /* Cap length at (num - 1) to leave room for \0 */
    if (size <= len)
        len = (size - 1);

    /* Copy as much of string as we can fit */
    memcpy(dest, src, len);

    /* explicit null termination */
    dest[len] = '\0';

    return dest;
}

/* Uses global var 'out_file_prefix' */
FILE *
my_fopen(const char *fname, const char *flag, int prompt) {
    FILE *fp;
    int Len;
    char *new_fname = NULL;
    char prompt_filename[256];

    /* Appends a prefix string for output files */
    if (out_file_prefix) {
        if (strchr(flag, 'w')) {
            Len = 1; /* NULL char */
            Len += strlen(out_file_prefix);
            Len += strlen(fname);
            new_fname = (char *) my_malloc(Len * sizeof(char));
            strcpy(new_fname, out_file_prefix);
            strcat(new_fname, fname);
            fname = new_fname;
        }
    }

    if (prompt) {
        int check_num_of_entered_values = scanf("%s", prompt_filename);
        while (getchar() != '\n')
            ;

        while (check_num_of_entered_values != 1) {
            vpr_printf(TIO_MESSAGE_ERROR,
                    "Was expecting one file name to be entered, with no spaces. You have entered %d parameters. Please try again: \n",
                    check_num_of_entered_values);
            check_num_of_entered_values = scanf("%s", prompt_filename);
        }
        fname = prompt_filename;
    }

    if (NULL == (fp = fopen(fname, flag))) {
        vpr_printf(TIO_MESSAGE_ERROR,
                "Error opening file %s for %s access: %s.\n", fname, flag,
                strerror(errno));
        exit(1);
    }

    if (new_fname)
        free(new_fname);

    return (fp);
}

char *
my_strdup(const char *str) {
    int Len;
    char *Dst;

    if (str == NULL ) {
        return NULL ;
    }

    Len = 1 + strlen(str);
    Dst = (char *) my_malloc(Len * sizeof(char));
    memcpy(Dst, str, Len);

    return Dst;
}

int my_atoi(const char *str) {

    /* Returns the integer represented by the first part of the character       *
     * string.                                              */

    if (str[0] < '0' || str[0] > '9') {
        if (!(str[0] == '-' && str[1] >= '0' && str[1] <= '9')) {
            vpr_printf(TIO_MESSAGE_ERROR, "expected number instead of '%s'.\n",
                    str);
            exit(1);
        }
    }
    return (atoi(str));
}

void *
my_calloc(size_t nelem, size_t size) {
    void *ret;
    if (nelem == 0) {
        return NULL ;
    }

    if ((ret = calloc(nelem, size)) == NULL ) {
        vpr_printf(TIO_MESSAGE_ERROR,
                "Error:  Unable to calloc memory.  Aborting.\n");
        exit(1);
    }
    return (ret);
}

void *
my_malloc(size_t size) {
    void *ret;
    if (size == 0) {
        return NULL ;
    }

    if ((ret = malloc(size)) == NULL ) {
        vpr_printf(TIO_MESSAGE_ERROR,
                "Error:  Unable to malloc memory.  Aborting.\n");
        abort();
        exit(1);
    }
    return (ret);
}

void *
my_realloc(void *ptr, size_t size) {
    void *ret;

    if (size <= 0) {
        vpr_printf(TIO_MESSAGE_WARNING, "reallocating of size <= 0.\n");
    }

    ret = realloc(ptr, size);
    if (NULL == ret) {
        vpr_printf(TIO_MESSAGE_ERROR, "Unable to realloc memory. Aborting. "
                "ptr=%p, Size=%d.\n", ptr, (int) size);
        if (ptr == NULL ) {
            vpr_printf(TIO_MESSAGE_ERROR,
                    "my_realloc: ptr == NULL. Aborting.\n");
        }
        exit(1);
    }
    return (ret);
}

void *
my_chunk_malloc(size_t size, t_chunk *chunk_info) {

    /* This routine should be used for allocating fairly small data             *
     * structures where memory-efficiency is crucial.  This routine allocates   *
     * large "chunks" of data, and parcels them out as requested.  Whenever     *
     * it mallocs a new chunk it adds it to the linked list pointed to by       *
     * chunk_info->chunk_ptr_head.  This list can be used to free the       *
     * chunked memory.                              *
     * Information about the currently open "chunk" must be stored by the       *
     * user program.  chunk_info->mem_avail_ptr points to an int storing        *
     * how many bytes are left in the current chunk, while              *
     * chunk_info->next_mem_loc_ptr is the address of a pointer to the      *
     * next free bytes in the chunk.  To start a new chunk, simply set      *
     * chunk_info->mem_avail_ptr = 0.  Each independent set of data         *
     * structures should use a new chunk.                                       */

    /* To make sure the memory passed back is properly aligned, I must *
     * only send back chunks in multiples of the worst-case alignment  *
     * restriction of the machine.  On most machines this should be    *
     * a long, but on 64-bit machines it might be a long long or a     *
     * double.  Change the typedef below if this is the case.          */

    typedef long Align;

#define CHUNK_SIZE 32768
#define FRAGMENT_THRESHOLD 100

    char *tmp_ptr;
    int aligned_size;

    assert(chunk_info->mem_avail >= 0);

    if ((size_t) (chunk_info->mem_avail) < size) { /* Need to malloc more memory. */
        if (size > CHUNK_SIZE) { /* Too big, use standard routine. */
            tmp_ptr = (char *) my_malloc(size);

            /* When debugging, uncomment the code below to see if memory allocation size */
            /* makes sense */
            /*#ifdef DEBUG
             vpr_printf("NB:  my_chunk_malloc got a request for %d bytes.\n",
             size);
             vpr_printf("You should consider using my_malloc for such big requests.\n");
             #endif */

            assert(chunk_info != NULL);
            chunk_info->chunk_ptr_head = insert_in_vptr_list(
                    chunk_info->chunk_ptr_head, tmp_ptr);
            return (tmp_ptr);
        }

        if (chunk_info->mem_avail < FRAGMENT_THRESHOLD) { /* Only a small scrap left. */
            chunk_info->next_mem_loc_ptr = (char *) my_malloc(CHUNK_SIZE);
            chunk_info->mem_avail = CHUNK_SIZE;
            assert(chunk_info != NULL);
            chunk_info->chunk_ptr_head = insert_in_vptr_list(
                    chunk_info->chunk_ptr_head, chunk_info->next_mem_loc_ptr);
        }

        /* Execute else clause only when the chunk we want is pretty big,  *
         * and would leave too big an unused fragment.  Then we use malloc *
         * to allocate normally.                                           */

        else {
            tmp_ptr = (char *) my_malloc(size);
            assert(chunk_info != NULL);
            chunk_info->chunk_ptr_head = insert_in_vptr_list(
                    chunk_info->chunk_ptr_head, tmp_ptr);
            return (tmp_ptr);
        }
    }

    /* Find the smallest distance to advance the memory pointer and keep *
     * everything aligned.                                               */

    if (size % sizeof(Align) == 0) {
        aligned_size = size;
    } else {
        aligned_size = size + sizeof(Align) - size % sizeof(Align);
    }

    tmp_ptr = chunk_info->next_mem_loc_ptr;
    chunk_info->next_mem_loc_ptr += aligned_size;
    chunk_info->mem_avail -= aligned_size;
    return (tmp_ptr);
}

void free_chunk_memory(t_chunk *chunk_info) {

    /* Frees the memory allocated by a sequence of calls to my_chunk_malloc. */

    struct s_linked_vptr *curr_ptr, *prev_ptr;

    curr_ptr = chunk_info->chunk_ptr_head;

    while (curr_ptr != NULL ) {
        free(curr_ptr->data_vptr); /* Free memory "chunk". */
        prev_ptr = curr_ptr;
        curr_ptr = curr_ptr->next;
        free(prev_ptr); /* Free memory used to track "chunk". */
    }
    chunk_info->chunk_ptr_head = NULL;
    chunk_info->mem_avail = 0;
    chunk_info->next_mem_loc_ptr = NULL;
}

struct s_linked_vptr *
insert_in_vptr_list(struct s_linked_vptr *head, void *vptr_to_add) {

    /* Inserts a new element at the head of a linked list of void pointers. *
     * Returns the new head of the list.                                    */

    struct s_linked_vptr *linked_vptr;

    linked_vptr = (struct s_linked_vptr *) my_malloc(
            sizeof(struct s_linked_vptr));

    linked_vptr->data_vptr = vptr_to_add;
    linked_vptr->next = head;
    return (linked_vptr); /* New head of the list */
}

/* Deletes the element at the head of a linked list of void pointers. *
 * Returns the new head of the list.                                    */
struct s_linked_vptr *
delete_in_vptr_list(struct s_linked_vptr *head) {
    struct s_linked_vptr *linked_vptr;

    if (head == NULL )
        return NULL ;
    linked_vptr = head->next;
    free(head);
    return linked_vptr; /* New head of the list */
}

t_linked_int *
insert_in_int_list(t_linked_int * head, int data,
        t_linked_int ** free_list_head_ptr) {

    /* Inserts a new element at the head of a linked list of integers.  Returns  *
     * the new head of the list.  One argument is the address of the head of     *
     * a list of free ilist elements.  If there are any elements on this free    *
     * list, the new element is taken from it.  Otherwise a new one is malloced. */

    t_linked_int *linked_int;

    if (*free_list_head_ptr != NULL ) {
        linked_int = *free_list_head_ptr;
        *free_list_head_ptr = linked_int->next;
    } else {
        linked_int = (t_linked_int *) my_malloc(sizeof(t_linked_int));
    }

    linked_int->data = data;
    linked_int->next = head;
    return (linked_int);
}

void free_int_list(t_linked_int ** int_list_head_ptr) {

    /* This routine truly frees (calls free) all the integer list elements    * 
     * on the linked list pointed to by *head, and sets head = NULL.          */

    t_linked_int *linked_int, *next_linked_int;

    linked_int = *int_list_head_ptr;

    while (linked_int != NULL ) {
        next_linked_int = linked_int->next;
        free(linked_int);
        linked_int = next_linked_int;
    }

    *int_list_head_ptr = NULL;
}

void alloc_ivector_and_copy_int_list(t_linked_int ** list_head_ptr,
        int num_items, struct s_ivec *ivec, t_linked_int ** free_list_head_ptr) {

    /* Allocates an integer vector with num_items elements and copies the       *
     * integers from the list pointed to by list_head (of which there must be   *
     * num_items) over to it.  The int_list is then put on the free list, and   *
     * the list_head_ptr is set to NULL.                                        */

    t_linked_int *linked_int, *list_head;
    int i, *list;

    list_head = *list_head_ptr;

    if (num_items == 0) { /* Empty list. */
        ivec->nelem = 0;
        ivec->list = NULL;

        if (list_head != NULL ) {
            vpr_printf(TIO_MESSAGE_ERROR,
                    "alloc_ivector_and_copy_int_list: Copied %d elements, "
                            "but list at %p contains more.\n", num_items,
                    (void *) list_head);
            exit(1);
        }
        return;
    }

    ivec->nelem = num_items;
    list = (int *) my_malloc(num_items * sizeof(int));
    ivec->list = list;
    linked_int = list_head;

    for (i = 0; i < num_items - 1; i++) {
        list[i] = linked_int->data;
        linked_int = linked_int->next;
    }

    list[num_items - 1] = linked_int->data;

    if (linked_int->next != NULL ) {
        vpr_printf(TIO_MESSAGE_ERROR,
                "Error in alloc_ivector_and_copy_int_list:\n Copied %d elements, "
                        "but list at %p contains more.\n", num_items,
                (void *) list_head);
        exit(1);
    }

    linked_int->next = *free_list_head_ptr;
    *free_list_head_ptr = list_head;
    *list_head_ptr = NULL;
}

char *
my_fgets(char *buf, int max_size, FILE * fp) {
    /* Get an input line, update the line number and cut off *
     * any comment part.  A \ at the end of a line with no   *
     * comment part (#) means continue. my_fgets should give * 
     * identical results for Windows (\r\n) and Linux (\n)   *
     * newlines, since it replaces each carriage return \r   *
     * by a newline character \n.  Returns NULL after EOF.   */

    char ch;
    int i;

    cont = 0; /* line continued? */
    file_line_number++; /* global variable */

    for (i = 0; i < max_size - 1; i++) { /* Keep going until the line finishes or the buffer is full */

        ch = fgetc(fp);

        if (feof(fp)) { /* end of file */
            if (i == 0) {
                return NULL ; /* required so we can write while (my_fgets(...) != NULL) */
            } else { /* no newline before end of file - last line must be returned */
                buf[i] = '\0';
                return buf;
            }
        }

        if (ch == '#') { /* comment */
            buf[i] = '\0';
            while ((ch = fgetc(fp)) != '\n' && !feof(fp))
                ; /* skip the rest of the line */
            return buf;
        }

        if (ch == '\r' || ch == '\n') { /* newline (cross-platform) */
            if (i != 0 && buf[i - 1] == '\\') { /* if \ at end of line, line continued */
                cont = 1;
                buf[i - 1] = '\n'; /* May need this for tokens */
                buf[i] = '\0';
            } else {
                buf[i] = '\n';
                buf[i + 1] = '\0';
            }
            return buf;
        }

        buf[i] = ch; /* copy character into the buffer */

    }

    /* Buffer is full but line has not terminated, so error */
    vpr_printf(TIO_MESSAGE_ERROR,
            "Error on line %d -- line is too long for input buffer.\n",
            file_line_number);
    vpr_printf(TIO_MESSAGE_ERROR,
            "All lines must be at most %d characters long.\n", BUFSIZE - 2);
    exit(1);
}

char *
my_strtok(char *ptr, const char *tokens, FILE * fp, char *buf) {

    /* Get next token, and wrap to next line if \ at end of line.    *
     * There is a bit of a "gotcha" in strtok.  It does not make a   *
     * copy of the character array which you pass by pointer on the  *
     * first call.  Thus, you must make sure this array exists for   *
     * as long as you are using strtok to parse that line.  Don't    *
     * use local buffers in a bunch of subroutines calling each      *
     * other; the local buffer may be overwritten when the stack is  *
     * restored after return from the subroutine.                    */

    char *val;

    val = strtok(ptr, tokens);
    for (;;) {
        if (val != NULL || cont == 0)
            return (val);

        /* return unless we have a null value and a continuation line */
        if (my_fgets(buf, BUFSIZE, fp) == NULL )
            return (NULL );

        val = strtok(buf, tokens);
    }
}

void free_ivec_vector(struct s_ivec *ivec_vector, int nrmin, int nrmax) {

    /* Frees a 1D array of integer vectors.                              */

    int i;

    for (i = nrmin; i <= nrmax; i++)
        if (ivec_vector[i].nelem != 0)
            free(ivec_vector[i].list);

    free(ivec_vector + nrmin);
}

void free_ivec_matrix(struct s_ivec **ivec_matrix, int nrmin, int nrmax,
        int ncmin, int ncmax) {

    /* Frees a 2D matrix of integer vectors (ivecs).                     */

    int i, j;

    for (i = nrmin; i <= nrmax; i++) {
        for (j = ncmin; j <= ncmax; j++) {
            if (ivec_matrix[i][j].nelem != 0) {
                free(ivec_matrix[i][j].list);
            }
        }
    }

    free_matrix(ivec_matrix, nrmin, nrmax, ncmin, sizeof(struct s_ivec));
}

void free_ivec_matrix3(struct s_ivec ***ivec_matrix3, int nrmin, int nrmax,
        int ncmin, int ncmax, int ndmin, int ndmax) {

    /* Frees a 3D matrix of integer vectors (ivecs).                     */

    int i, j, k;

    for (i = nrmin; i <= nrmax; i++) {
        for (j = ncmin; j <= ncmax; j++) {
            for (k = ndmin; k <= ndmax; k++) {
                if (ivec_matrix3[i][j][k].nelem != 0) {
                    free(ivec_matrix3[i][j][k].list);
                }
            }
        }
    }

    free_matrix3(ivec_matrix3, nrmin, nrmax, ncmin, ncmax, ndmin,
            sizeof(struct s_ivec));
}

void **
alloc_matrix(int nrmin, int nrmax, int ncmin, int ncmax, size_t elsize) {

    /* allocates an generic matrix with nrmax-nrmin + 1 rows and ncmax - *
     * ncmin + 1 columns, with each element of size elsize. i.e.         *
     * returns a pointer to a storage block [nrmin..nrmax][ncmin..ncmax].*
     * Simply cast the returned array pointer to the proper type.        */

    int i;
    char **cptr;

    cptr = (char **) my_malloc((nrmax - nrmin + 1) * sizeof(char *));
    cptr -= nrmin;
    for (i = nrmin; i <= nrmax; i++) {
        cptr[i] = (char *) my_malloc((ncmax - ncmin + 1) * elsize);
        cptr[i] -= ncmin * elsize / sizeof(char); /* sizeof(char) = 1 */
    }
    return ((void **) cptr);
}

/* NB:  need to make the pointer type void * instead of void ** to allow   *
 * any pointer to be passed in without a cast.                             */

void free_matrix(void *vptr, int nrmin, int nrmax, int ncmin, size_t elsize) {
    int i;
    char **cptr;

    cptr = (char **) vptr;

    for (i = nrmin; i <= nrmax; i++)
        free(cptr[i] + ncmin * elsize / sizeof(char));
    free(cptr + nrmin);
}

void ***
alloc_matrix3(int nrmin, int nrmax, int ncmin, int ncmax, int ndmin, int ndmax,
        size_t elsize) {

    /* allocates a 3D generic matrix with nrmax-nrmin + 1 rows, ncmax -  *
     * ncmin + 1 columns, and a depth of ndmax-ndmin + 1, with each      *
     * element of size elsize. i.e. returns a pointer to a storage block *
     * [nrmin..nrmax][ncmin..ncmax][ndmin..ndmax].  Simply cast the      *
     *  returned array pointer to the proper type.                       */

    int i, j;
    char ***cptr;

    cptr = (char ***) my_malloc((nrmax - nrmin + 1) * sizeof(char **));
    cptr -= nrmin;
    for (i = nrmin; i <= nrmax; i++) {
        cptr[i] = (char **) my_malloc((ncmax - ncmin + 1) * sizeof(char *));
        cptr[i] -= ncmin;
        for (j = ncmin; j <= ncmax; j++) {
            cptr[i][j] = (char *) my_malloc((ndmax - ndmin + 1) * elsize);
            cptr[i][j] -= ndmin * elsize / sizeof(char); /* sizeof(char) = 1) */
        }
    }
    return ((void ***) cptr);
}

void ****
alloc_matrix4(int nrmin, int nrmax, int ncmin, int ncmax, int ndmin, int ndmax,
        int nemin, int nemax, size_t elsize) {

    /* allocates a 3D generic matrix with nrmax-nrmin + 1 rows, ncmax -  *
     * ncmin + 1 columns, and a depth of ndmax-ndmin + 1, with each      *
     * element of size elsize. i.e. returns a pointer to a storage block *
     * [nrmin..nrmax][ncmin..ncmax][ndmin..ndmax].  Simply cast the      *
     *  returned array pointer to the proper type.                       */

    int i, j, k;
    char ****cptr;

    cptr = (char ****) my_malloc((nrmax - nrmin + 1) * sizeof(char ***));
    cptr -= nrmin;
    for (i = nrmin; i <= nrmax; i++) {
        cptr[i] = (char ***) my_malloc((ncmax - ncmin + 1) * sizeof(char **));
        cptr[i] -= ncmin;
        for (j = ncmin; j <= ncmax; j++) {
            cptr[i][j] = (char **) my_malloc(
                    (ndmax - ndmin + 1) * sizeof(char *));
            cptr[i][j] -= ndmin;
            for (k = ndmin; k <= ndmax; k++) {
                cptr[i][j][k] = (char *) my_malloc(
                        (nemax - nemin + 1) * elsize);
                cptr[i][j][k] -= nemin * elsize / sizeof(char); /* sizeof(char) = 1) */
            }
        }
    }
    return ((void ****) cptr);
}

void print_int_matrix3(int ***vptr, int nrmin, int nrmax, int ncmin, int ncmax,
        int ndmin, int ndmax, char *file) {
    FILE *outfile;
    int i, j, k;

    outfile = my_fopen(file, "w", 0);

    for (k = nrmin; k <= nrmax; ++k) {
        fprintf(outfile, "Plane %d\n", k);
        for (j = ncmin; j <= ncmax; ++j) {
            for (i = ndmin; i <= ndmax; ++i) {
                fprintf(outfile, "%d ", vptr[k][j][i]);
            }
            fprintf(outfile, "\n");
        }
        fprintf(outfile, "\n");
    }

    fclose(outfile);
}

void free_matrix3(void *vptr, int nrmin, int nrmax, int ncmin, int ncmax,
        int ndmin, size_t elsize) {
    int i, j;
    char ***cptr;

    cptr = (char ***) vptr;

    for (i = nrmin; i <= nrmax; i++) {
        for (j = ncmin; j <= ncmax; j++)
            free(cptr[i][j] + ndmin * elsize / sizeof(char));
        free(cptr[i] + ncmin);
    }
    free(cptr + nrmin);
}

void free_matrix4(void *vptr, int nrmin, int nrmax, int ncmin, int ncmax,
        int ndmin, int ndmax, int nemin, size_t elsize) {
    int i, j, k;
    char ****cptr;

    cptr = (char ****) vptr;

    for (i = nrmin; i <= nrmax; i++) {
        for (j = ncmin; j <= ncmax; j++) {
            for (k = ndmin; k <= ndmax; k++)
                free(cptr[i][j][k] + nemin * elsize / sizeof(char));
            free(cptr[i][j] + ndmin * elsize / sizeof(char));
        }
        free(cptr[i] + ncmin);
    }
    free(cptr + nrmin);
}

/* Portable random number generator defined below.  Taken from ANSI C by  *
 * K & R.  Not a great generator, but fast, and good enough for my needs. */

#define IA 1103515245u
#define IC 12345u
#define IM 2147483648u
#define CHECK_RAND

static unsigned int current_random = 0;

void my_srandom(int seed) {
    current_random = (unsigned int) seed;
}

int my_irand(int imax) {

    /* Creates a random integer between 0 and imax, inclusive.  i.e. [0..imax] */

    int ival;

    /* current_random = (current_random * IA + IC) % IM; */
    current_random = current_random * IA + IC; /* Use overflow to wrap */
    ival = current_random & (IM - 1); /* Modulus */
    ival = (int) ((float) ival * (float) (imax + 0.999) / (float) IM);

#ifdef CHECK_RAND
    if ((ival < 0) || (ival > imax)) {
        if (ival == imax + 1) {
            /* Due to random floating point rounding, sometimes above calculation gives number greater than ival by 1 */
            ival = imax;
        } else {
            vpr_printf(TIO_MESSAGE_ERROR,
                    "Bad value in my_irand, imax = %d  ival = %d\n", imax,
                    ival);
            exit(1);
        }
    }
#endif

    return (ival);
}

float my_frand(void) {

    /* Creates a random float between 0 and 1.  i.e. [0..1).        */

    float fval;
    int ival;

    current_random = current_random * IA + IC; /* Use overflow to wrap */
    ival = current_random & (IM - 1); /* Modulus */
    fval = (float) ival / (float) IM;

#ifdef CHECK_RAND
    if ((fval < 0) || (fval > 1.)) {
        vpr_printf(TIO_MESSAGE_ERROR, "Bad value in my_frand, fval = %g\n",
                fval);
        exit(1);
    }
#endif

    return (fval);
}

boolean file_exists(const char * filename) {
    FILE * file;

    if (filename == NULL ) {
        return FALSE;
    }

    file = fopen(filename, "r");
    if (file) {
        fclose(file);
        return TRUE;
    }
    return FALSE;
}

int ipow(int base, int exp) {
    int result = 1;

    assert(exp >= 0);

    while (exp) {
        if (exp & 1)
            result *= base;
        exp >>= 1;
        base *= base;
    }

    return result;
}