Negative base numbers: Difference between revisions

=={{header|C}}==

{{trans|modula-2}}

<lang c>#include <stdio.h>

const char DIGITS[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

const int DIGITS_LEN = 64;

void encodeNegativeBase(long n, long base, char *out) {

char *ptr = out;

if (base > -1 || base < -62) {

/* Bounds check*/

out = "";

return;

}

if (n == 0) {

/* Trivial case */

out = "0";

return;

}

/* Convert the number into a string (in reverse) */

while (n != 0) {

long rem = n % base;

n = n / base;

if (rem < 0) {

n++;

rem = rem - base;

}

*ptr = DIGITS[rem];

ptr++;

}

*ptr = 0;

/* Reverse the current string to get the final result */

ptr--;

while (out < ptr) {

char t = *out;

*out = *ptr;

*ptr = t;

out++;

ptr--;

}

return;

}

long decodeNegativeBase(const char* ns, long base) {

long value, bb;

int i;

const char *ptr;

if (base < -62 || base > -1) {

/* Bounds check */

return 0;

}

if (ns[0] == 0 || (ns[0] == '0' && ns[1] == 0)) {

/* Trivial case */

return 0;

}

/* Find the end of the string */

ptr = ns;

while (*ptr != 0) {

ptr++;

}

/* Convert */

value = 0;

bb = 1;

ptr--;

while (ptr >= ns) {

for (i = 0; i < DIGITS_LEN; i++) {

if (*ptr == DIGITS[i]) {

value = value + i * bb;

bb = bb * base;

break;

}

}

ptr--;

}

return value;

}

void driver(long n, long b) {

char buf[64];

long value;

encodeNegativeBase(n, b, buf);

printf("%12d encoded in base %3d = %12s\n", n, b, buf);

value = decodeNegativeBase(buf, b);

printf("%12s decoded in base %3d = %12d\n", buf, b, value);

printf("\n");

}

int main() {

driver(10, -2);

driver(146, -3);

driver(15, -10);

driver(12, -62);

return 0;

}</lang>

{{out}}

<pre> 10 encoded in base -2 = 11110

11110 decoded in base -2 = 10

146 encoded in base -3 = 21102

21102 decoded in base -3 = 146

15 encoded in base -10 = 195

195 decoded in base -10 = 15

12 encoded in base -62 = C

C decoded in base -62 = 12</pre>