Day25

day25/snafu.c

@@ -0,0 +1,102 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define BUFFER_SIZE 64
+#define MAGIC_NUMBER 5
+
+long powNum(long, long);
+long snafu_to_human(char*, int);
+void human_to_snafu(char*, long);
+
+int main() {
+    char buf[BUFFER_SIZE], *p, c;
+    memset(buf, 0, BUFFER_SIZE);
+    p = buf;
+    long sum = 0;
+
+    while ((c = getchar()) != EOF) {
+        *p++ = c;
+        if (c == '\n') {
+            sum += snafu_to_human(p-2, p-buf);
+            memset(buf, 0, BUFFER_SIZE);
+            p = buf;
+        }
+    }
+
+    printf("Sum in decimal: %li\n", sum);
+    char snafu[64];
+    memset(snafu, 0, 64);
+    human_to_snafu(snafu, sum);
+    printf("Sum in SNAFU: %s\n", snafu);
+}
+
+long powNum(long b, long e) {
+    long result = 1;
+    for (int i = 0; i < e; i++) {
+        result *= b;
+    }
+
+    return result;
+}
+
+long snafu_to_human(char* p, int len) {
+    long result = 0;
+    for (int i = 0; i < len; i++) {
+        switch(*(p-i)) {
+            case '0':
+                break;
+            case '1':
+                result += powNum(MAGIC_NUMBER, i);
+                break;
+            case '2':
+                result += 2*powNum(MAGIC_NUMBER, i);
+                break;
+            case '-':
+                result += -powNum(MAGIC_NUMBER, i);
+                break;
+            case '=':
+                result += -2*powNum(MAGIC_NUMBER, i);
+                break;
+        }
+    }
+
+    return result;
+}
+
+void human_to_snafu(char* p, long decimal) {
+    char buf[64], *q;
+    memset(buf, 0, 64);
+
+    long num = decimal;
+    int len = 0;
+    int remainder = 0;
+
+    while (num != 0) {
+        int numeric = num % MAGIC_NUMBER;
+        num /= MAGIC_NUMBER;
+        numeric += remainder;
+        remainder = 0;
+        if (numeric > 2) {
+            remainder = 1;
+            numeric = numeric - MAGIC_NUMBER;
+        }
+        if (numeric == -1) {
+            buf[len] = '-';
+        } else if (numeric == -2) {
+            buf[len] = '=';
+        } else {
+            buf[len] = '0' + numeric;
+        }
+        len++;
+    }
+
+    if (remainder) {
+        buf[len] = '1';
+        len++;
+    }
+
+    for (int i = 0; i <= len; i++) {
+        *(p+len-i-1) = buf[i];
+    }
+}