Add hamming distance function

ex06/input.txt

@@ -0,0 +1,64 @@
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ex06/main.c

@@ -0,0 +1,28 @@
+#include "utils.h"
+#include <ctype.h>
+#include <stdio.h>
+#include <string.h>
+
+int main(int argc, char *argv[]) {
+  if (argc < 2) {
+    printf("Usage: %s <filename>\n", argv[0]);
+    return EXIT_FAILURE;
+  }
+
+  const char *filename = argv[1];
+
+  FILE *fp = fopen(filename, "r");
+  if (fp == NULL) {
+    printf("Error opening file %s\n", filename);
+    return EXIT_FAILURE;
+  }
+
+  printf("%u\n", hamming("this is a test", "wokka wokka!!!"));
+
+  if (fclose(fp)) {
+    printf("Error closing file %s\n", filename);
+    return EXIT_FAILURE;
+  }
+
+  return EXIT_SUCCESS;
+}

meson.build

@@ -8,3 +8,4 @@ executable('ex02', ['ex02/main.c', 'utils.c'], dependencies: m_dep)
 executable('ex03', ['ex03/main.c', 'utils.c'], dependencies: m_dep)
 executable('ex04', ['ex04/main.c', 'utils.c'], dependencies: m_dep)
 executable('ex05', ['ex05/main.c', 'utils.c'], dependencies: m_dep)
+executable('ex06', ['ex06/main.c', 'utils.c'], dependencies: m_dep)

utils.c

@@ -3,6 +3,20 @@
 #include <math.h>
 #include <string.h>
 
+#define min(a, b)                                                              \
+  ({                                                                           \
+    __typeof__(a) _a = (a);                                                    \
+    __typeof__(b) _b = (b);                                                    \
+    _a > _b ? _b : _a;                                                         \
+  })
+
+#define max(a, b)                                                              \
+  ({                                                                           \
+    __typeof__(a) _a = (a);                                                    \
+    __typeof__(b) _b = (b);                                                    \
+    _a > _b ? _a : _b;                                                         \
+  })
+
 unsigned char hex_to_byte(const char c) {
   if (isdigit(c)) {
     return c - '0';
@@ -69,3 +83,18 @@ double frequency_score(unsigned char *buf, size_t len) {
   }
   return chi2;
 }
+
+unsigned int hamming(const char *s1, const char *s2) {
+  unsigned int len1 = strlen(s1);
+  unsigned int len2 = strlen(s2);
+
+  unsigned int res = 0;
+  for (size_t i = 0; i < min(len1, len2); ++i) {
+    unsigned int n = s1[i] ^ s2[i];
+    while (n) {
+      res += n & 1;
+      n >>= 1;
+    }
+  }
+  return res;
+}

utils.h

@@ -8,5 +8,6 @@ size_t hex_to_bytes(unsigned char *out, const char hex[static 1]);
 unsigned char *bytes_to_base64(unsigned char *out,
                                const unsigned char in[static 1], size_t len);
 double frequency_score(unsigned char *buf, size_t len);
+unsigned int hamming(const char *s1, const char *s2);
 
 #endif /* UTILS_H */