add few more files

4 files changed, 105 insertions, 2 deletions

diff --git a/Makefile b/Makefile
index 4a52efa..5c2f6c5 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 BINS = ascii class depipe_strings dup fpipe pipe realloc strpbrk strsep \
-       tokenizer getopt
+       tokenizer getopt prime_mask
 CC = gcc
 DBGFLAGS = -g -O0
 ifdef DEBUG
diff --git a/keygen_args.c b/keygen_args.c
index 6c12e9c..2eafa5f 100644
--- a/keygen_args.c
+++ b/keygen_args.c
@@ -70,7 +70,7 @@ int keygen_args(int argc, char **argv)
     if (opt_args == 2)
     {
         pubkey = strdup(argv[fname_arg]);
-        prikey = strdup(argv[fname_arg+1]);        
+        prikey = strdup(argv[fname_arg+1]);
     }
     else if (fname_f) /* opt_args equals 0 here */
     {
diff --git a/miller_rabin.c b/miller_rabin.c
new file mode 100644
index 0000000..3794ee6
--- /dev/null
+++ b/miller_rabin.c
@@ -0,0 +1,80 @@
+/* Source:
+ * http://en.literateprograms.org/Miller-Rabin_primality_test_%28C%29
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define COMPOSITE 0
+#define PRIME     1
+
+unsigned short modular_exponent_16(unsigned short base, unsigned short power,
+                                   unsigned short modulus)
+{
+    unsigned long result = 1;
+
+    int i;
+    for (i = 15; i >= 0; i--)
+    {
+        result = (result*result) % modulus;
+
+        if (power & (1 << i))
+            result = (result*base) % modulus;
+    }
+
+    return (unsigned short) result; /* will not truncate since modulus is a unsigned short */
+}
+
+int miller_rabin_pass_16(unsigned short a, unsigned short n)
+{
+    unsigned short a_to_power, s, d, i;
+
+    s = 0;
+    d = n - 1;
+    while ((d % 2) == 0)
+    {
+        d /= 2;
+        s++;
+    }
+
+    a_to_power = modular_exponent_16(a, d, n);
+
+    if (a_to_power == 1)
+        return PRIME;
+
+    for (i = 0; i < s-1; i++)
+    {
+        if (a_to_power == n-1)
+            return PRIME;
+        a_to_power = modular_exponent_16(a_to_power, 2, n);
+    }
+
+    if (a_to_power == n-1)
+        return PRIME;
+
+    return COMPOSITE;
+}
+
+int miller_rabin_16(unsigned short n)
+{
+    if (n <= 1)
+        return COMPOSITE;
+    if (n == 2)
+        return PRIME;
+    if (miller_rabin_pass_16( 2, n) == PRIME &&
+        (n <= 7  || miller_rabin_pass_16( 7, n) == PRIME) &&
+        (n <= 61 || miller_rabin_pass_16(61, n) == PRIME))
+        return PRIME;
+    else
+        return COMPOSITE;
+}
+
+int main(int argc, char* argv[])
+{
+    unsigned short n = (unsigned short) atoi(argv[1]);
+    puts(miller_rabin_16(n) == PRIME ? "PRIME" : "COMPOSITE");
+
+    return 0;
+}
+
diff --git a/prime_mask.c b/prime_mask.c
new file mode 100644
index 0000000..d6b02d0
--- /dev/null
+++ b/prime_mask.c
@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#define LOW_BIT_ON        1 << 0
+#define FIRST_TWO_BITS_ON 3 << ((sizeof(unsigned int) * 8) - 2)
+
+int main(int argc, char **argv)
+{
+    /* seed rand() */
+    srand((unsigned int ) time(NULL));
+
+    unsigned int x = rand();
+    printf("x before masking: %10u 0x%08x\n", x, x);
+
+    x |= LOW_BIT_ON;
+    x |= FIRST_TWO_BITS_ON;
+
+    printf("x after masking : %10u 0x%08x\n", x, x);
+
+    return 0;
+}
+