Make sure that each MIX permutation has maximum distance to its direct predecessor.

diff --git a/tools/GenTables/src/gen_table_mix.c b/tools/GenTables/src/gen_table_mix.c
index 39fbc24..19032c5 100644 (file)
--- a/tools/GenTables/src/gen_table_mix.c
+++ b/tools/GenTables/src/gen_table_mix.c
@@ -36,9 +36,9 @@
 
 #define HASH_LEN 384U
 
-#define ROW_NUM 251U                    /*total number of rows*/
+#define ROW_NUM 256U                    /*total number of rows*/
 #define ROW_LEN (HASH_LEN / CHAR_BIT)   /*number of indices per row*/
-#define DISTANCE_MIN (ROW_LEN - 1U)     /*min. hamming distance*/
+#define DISTANCE_MIN (ROW_LEN - 2U)     /*min. hamming distance*/
 
 #undef ENABLE_TRACE
 
@@ -107,6 +107,7 @@ static inline void random_permutation(msws_t rand, uint8_t *const row_buffer)
 
 static inline void swap_multiple_random(msws_t rand, uint8_t *const row_buffer, const uint_fast16_t count)
 {
+       uint_fast16_t a_prev = UINT_FAST16_MAX, b_prev = UINT_FAST16_MAX;
        for (uint_fast16_t i = 0U; i < count; ++i)
        {
                uint_fast16_t a, b;
@@ -115,8 +116,8 @@ static inline void swap_multiple_random(msws_t rand, uint8_t *const row_buffer,
                        a = msws_uint32_max(rand, ROW_LEN);
                        b = msws_uint32_max(rand, ROW_LEN);
                } 
-               while(a == b);
-               swap(row_buffer, a, b);
+               while((a == b) || (a == a_prev) || (a == b_prev) || (b == a_prev) || (b == b_prev));
+               swap(row_buffer, (a_prev = a), (b_prev = b));
        }
 }
 
@@ -157,9 +158,9 @@ static inline uint_fast16_t check_permutation(const uint_fast16_t index, const u
 {
        uint_fast16_t error = 0U, failed = 0U;
        uint_fast16_t distance = row_distance(&INDICES[0], &row_buffer[0]);
-       if (distance < DISTANCE_MIN)
+       if (distance < ROW_LEN)
        {
-               error = DISTANCE_MIN - distance;
+               error = ROW_LEN - distance;
                failed = 1U;
                if (ERROR_ACC(failed, error) >= limit)
                {
@@ -169,9 +170,10 @@ static inline uint_fast16_t check_permutation(const uint_fast16_t index, const u
        for (uint_fast16_t i = 0; i < index; ++i)
        {
                distance = row_distance(&g_table[i][0], &row_buffer[0]);
-               if (distance < DISTANCE_MIN)
+               const uint_fast16_t distance_min = (i != (index - 1U)) ? DISTANCE_MIN : ROW_LEN;
+               if (distance < distance_min)
                {
-                       error = max_ui16(error, DISTANCE_MIN - distance);
+                       error = max_ui16(error, distance_min - distance);
                        failed++;
                        if (ERROR_ACC(failed, error) >= limit)
                        {