Add current version of libSRTP from CVS.

libsrtp/test/lfsr.c

+/*
+ * lfsr.c
+ *
+ */
+
+
+#include <stdio.h>
+#include "datatypes.h"
+
+uint32_t 
+parity(uint32_t x) {
+
+  x ^= (x >> 16);
+  x ^= (x >> 8);
+  x ^= (x >> 4);
+  x ^= (x >> 2);
+  x ^= (x >> 1);
+
+  return x & 1;
+}
+
+
+/* typedef struct { */
+/*   uint32_t register[8]; */
+/* } lfsr_t; */
+
+void
+compute_period(uint32_t feedback_polynomial) {
+  int i;
+  v32_t lfsr;
+  v32_t mask;
+
+  mask.value = feedback_polynomial;
+  lfsr.value = 1;
+
+  printf("polynomial: %s\t", v32_bit_string(mask));
+
+  for (i=0; i < 256; i++) {
+/*     printf("%s\n", v32_bit_string(lfsr)); */
+    if (parity(mask.value & lfsr.value))
+      lfsr.value = ((lfsr.value << 1) | 1) & 0xff;
+    else
+      lfsr.value = (lfsr.value << 1) & 0xff;
+    
+    /* now halt if we're back at the initial state */
+    if (lfsr.value == 1) {
+      printf("period: %d\n", i);
+      break;
+    }
+  }
+}
+
+uint32_t poly0 = 223;
+
+
+uint32_t polynomials[39] = {
+31, 
+47,
+55,
+59,
+61,
+79,
+87,
+91,
+103,
+107,
+109,
+115,
+117,
+121,
+143,
+151,
+157,
+167,
+171,
+173,
+179,
+181,
+185,
+199,
+203,
+205,
+211,
+213,
+227,
+229,
+233, 
+241,
+127,
+191,
+223, 
+239,
+247,
+251,
+253 
+};
+
+char binary_string[32];
+
+char *
+u32_bit_string(uint32_t x, unsigned int length) {
+  unsigned int mask;
+  int index;
+ 
+  mask = 1 << length;
+  index = 0;
+  for (; mask > 0; mask >>= 1)
+    if ((x & mask) == 0)
+      binary_string[index++] = '0';
+    else
+      binary_string[index++] = '1';
+
+  binary_string[index++] = 0;  /* NULL terminate string */
+  return binary_string;
+}
+
+extern int octet_weight[256];
+
+unsigned int 
+weight(uint32_t poly) {
+  int wt = 0;
+
+  /* note: endian-ness makes no difference */
+  wt += octet_weight[poly        & 0xff]; 
+  wt += octet_weight[(poly >> 8) & 0xff];
+  wt += octet_weight[(poly >> 16) & 0xff];
+  wt += octet_weight[(poly >> 24)];
+
+  return wt;
+}
+
+#define MAX_PERIOD 65535
+
+#define debug_print 0
+
+int
+period(uint32_t poly) {
+  int i;
+  uint32_t x;
+
+
+  /* set lfsr to 1 */
+  x = 1;
+#if debug_print
+  printf("%d:\t%s\n", 0, u32_bit_string(x,8));
+#endif
+  for (i=1; i < MAX_PERIOD; i++) {
+    if (x & 1) 
+      x = (x >> 1) ^ poly;
+    else
+      x = (x >> 1);
+
+#if debug_print
+    /* print for a sanity check */
+    printf("%d:\t%s\n", i, u32_bit_string(x,8));
+#endif
+
+    /* check for return to original value */
+    if (x == 1)
+      return i;
+  }
+  return i;
+}
+
+/*
+ * weight distribution computes the weight distribution of the
+ * code generated by the polynomial poly
+ */
+
+#define MAX_LEN    8
+#define MAX_WEIGHT (1 << MAX_LEN)
+
+int A[MAX_WEIGHT+1];
+
+void
+weight_distribution2(uint32_t poly, int *A) {
+  int i;
+  uint32_t x;
+
+  /* zeroize array */
+  for (i=0; i < MAX_WEIGHT+1; i++)
+    A[i] = 0;
+
+  /* loop over all input sequences */
+  
+  
+  /* set lfsr to 1 */
+  x = 1;
+#if debug_print
+  printf("%d:\t%s\n", 0, u32_bit_string(x,8));
+#endif
+  for (i=1; i < MAX_PERIOD; i++) {
+    if (x & 1) 
+      x = (x >> 1) ^ poly;
+    else
+      x = (x >> 1);
+
+#if debug_print
+    /* print for a sanity check */
+    printf("%d:\t%s\n", i, u32_bit_string(x,8));
+#endif
+    
+    /* increment weight */
+    wt += (x & 1);
+
+    /* check for return to original value */
+    if (x == 1)
+      break;
+  }
+
+  /* set zero */
+  A[0] = 0;
+}
+
+
+void
+weight_distribution(uint32_t poly, int *A) {
+  int i;
+  uint32_t x;
+
+  /* zeroize array */
+  for (i=0; i < MAX_WEIGHT+1; i++)
+    A[i] = 0;
+
+  /* set lfsr to 1 */
+  x = 1;
+#if debug_print
+  printf("%d:\t%s\n", 0, u32_bit_string(x,8));
+#endif
+  for (i=1; i < MAX_PERIOD; i++) {
+    if (x & 1) 
+      x = (x >> 1) ^ poly;
+    else
+      x = (x >> 1);
+
+#if debug_print
+    /* print for a sanity check */
+    printf("%d:\t%s\n", i, u32_bit_string(x,8));
+#endif
+
+    /* compute weight, increment proper element */
+    A[weight(x)]++;
+
+    /* check for return to original value */
+    if (x == 1)
+      break;
+  }
+
+  /* set zero */
+  A[0] = 0;
+}
+
+
+
+
+int
+main () {
+
+  int i,j;
+  v32_t x;
+  v32_t p;
+
+  /* originally 0xaf */
+  p.value = 0x9;
+
+  printf("polynomial: %s\tperiod: %d\n",  
+           u32_bit_string(p.value,8), period(p.value)); 
+ 
+   /* compute weight distribution */
+  weight_distribution(p.value, A);
+  
+  /* print weight distribution */
+  for (i=0; i <= 8; i++) {
+    printf("A[%d]: %d\n", i, A[i]);
+  }
+  
+#if 0
+  for (i=0; i < 39; i++) {
+     printf("polynomial: %s\tperiod: %d\n",  
+           u32_bit_string(polynomials[i],8), period(polynomials[i])); 
+   
+     /* compute weight distribution */
+     weight_distribution(p.value, A);
+     
+     /* print weight distribution */
+     for (j=0; j <= 8; j++) {
+       printf("A[%d]: %d\n", j, A[j]);
+     }   
+  }
+#endif
+
+  { 
+    int bits = 8;
+    uint32_t y;
+    for (y=0; y < (1 << bits); y++) {
+      printf("polynomial: %s\tweight: %d\tperiod: %d\n", 
+             u32_bit_string(y,bits), weight(y), period(y));
+      
+      /* compute weight distribution */
+      weight_distribution(y, A);
+      
+      /* print weight distribution */
+      for (j=0; j <= 8; j++) {
+        printf("A[%d]: %d\n", j, A[j]);
+      }     
+    }
+  }
+
+  return 0;
+}