Initial commit: challenge 1

ex01/main.c

@@ -0,0 +1,51 @@
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+size_t hex_to_binary(unsigned char *out, const char hex[static 1]) {
+  for (size_t i = 0; i < strlen(hex); ++i) {
+    char c = tolower(hex[i]);
+    unsigned char value;
+    if (isdigit(c)) {
+      value = c - '0';
+    } else {
+      value = 10 + c - 'a';
+    }
+    if (i % 2 == 0) {
+      value <<= 4;
+    }
+    out[i / 2] += value;
+  }
+  return strlen(hex) / 2 + strlen(hex) % 2;
+}
+
+unsigned char *binary_to_base64(unsigned char *out,
+                                const unsigned char in[static 1], size_t len) {
+  static const unsigned char base64_table[65] =
+      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+  for (size_t i = 0; i < len - 2; i += 3) {
+    size_t j = i / 3 * 4;
+    out[j] = base64_table[in[i] >> 2];
+    out[j+1] = base64_table[((in[i] & 0x03) << 4) | (in[i+1] >> 4)];
+    out[j+2] = base64_table[((in[i+1] & 0x0f) << 2) | (in[i+2] >> 6)];
+    out[j+3] = base64_table[in[i+2] & 0x3f];
+  }
+  return out;
+}
+
+int main(int argc, char *argv[argc + 1]) {
+  if (argc < 2) {
+    printf("Usage: %s <hex>\n", argv[0]);
+    return EXIT_FAILURE;
+  }
+
+  unsigned char buf[512] = {0};
+  size_t len = hex_to_binary(buf, argv[1]);
+  unsigned char out[512] = {'\0'};
+  binary_to_base64(out, buf, len);
+  printf("%s\n", out);
+
+  return EXIT_SUCCESS;
+}