Data commit

Task/Negative-base-numbers/C/negative-base-numbers.c

@@ -0,0 +1,103 @@
+#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;
+}