From 880758c7d5d805440e2239080840486503013bf8 Mon Sep 17 00:00:00 2001
From: Adam Spragg <adam@spra.gg>
Date: Thu, 29 Dec 2022 09:51:45 +0000
Subject: Solve puzzle 25 part 1

---
 25.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 25.c

(limited to '25.c')

diff --git a/25.c b/25.c
new file mode 100644
index 0000000..b0f7293
--- /dev/null
+++ b/25.c
@@ -0,0 +1,100 @@
+
+#include <stdio.h>
+
+
+// Only works for positive numbers so far!
+char *
+snafu(char * dest, size_t len, long n)
+{
+	size_t i = 0, j;
+
+	// Build string in reverse.
+	while (n && i < len) {
+		int d = n % 5;
+
+		switch (d) {
+		case 0:
+		case 1:
+		case 2:
+			dest[i++] = '0' + d;
+			break;
+
+		case 3:
+			dest[i++] = '=';
+			n += 5;
+			break;
+
+		case 4:
+			dest[i++] = '-';
+			n += 5;
+			break;
+		}
+
+		n /= 5;
+	}
+
+	dest[i] = '\0';
+
+	// Reverse string to be right way around
+	for (j = 0; j < i / 2; ++j) {
+		char tmp = dest[j];
+		dest[j] = dest[i - 1 - j];
+		dest[i - 1 - j] = tmp;
+	}
+
+	return dest;
+}
+
+
+int
+main()
+{
+	long i = 0, total = 0;
+	int c;
+	char buf[BUFSIZ];
+
+	while ((c = fgetc(stdin)) != EOF) {
+		switch (c) {
+		case '2':
+			i *= 5;
+			i += 2;
+			break;
+
+		case '1':
+			i *= 5;
+			i += 1;
+			break;
+
+		case '0':
+			i *= 5;
+			break;
+
+		case '-':
+			i *= 5;
+			i -= 1;
+			break;
+
+		case '=':
+			i *= 5;
+			i -= 2;
+			break;
+
+		case '\n':
+#if 0
+			fprintf(stderr, "%s (%ld)\n", snafu(buf, sizeof(buf), i), i);
+#endif
+			total += i;
+			i = 0;
+			break;
+
+		default:
+			fprintf(stderr, "Unexpected input: %c\n", c);
+			return -1;
+		}
+	}
+
+	printf("Total: %s (%ld)\n", snafu(buf, sizeof(buf), total), total);
+
+	return 0;
+}
+
-- 
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