restructure havoc

src/afl-fuzz-one.c

@@ -1997,16 +1997,19 @@ havoc_stage:
   /* We essentially just do several thousand runs (depending on perf_score)
      where we take the input file and make random stacked tweaks. */
 
+#define MAX_HAVOC_ENTRY 59                                      /* 55 to 60 */
+
   u32 r_max, r;
 
-  r_max = 15 + ((afl->extras_cnt + afl->a_extras_cnt) ? 2 : 0);
+  r_max = (MAX_HAVOC_ENTRY + 1) + (afl->extras_cnt ? 4 : 0) +
+          (afl->a_extras_cnt ? 2 : 0);
 
   if (unlikely(afl->expand_havoc && afl->ready_for_splicing_count > 1)) {
 
     /* add expensive havoc cases here, they are activated after a full
        cycle without finds happened */
 
-    r_max++;
+    r_max += 4;
 
   }
 
@@ -2015,7 +2018,7 @@ havoc_stage:
 
     /* add expensive havoc cases here if there is no findings in the last 5s */
 
-    r_max++;
+    r_max += 4;
 
   }
 
@@ -2069,7 +2072,7 @@ havoc_stage:
 
       switch ((r = rand_below(afl, r_max))) {
 
-        case 0:
+        case 0 ... 3: {
 
           /* Flip a single bit somewhere. Spooky! */
 
@@ -2080,7 +2083,9 @@ havoc_stage:
           FLIP_BIT(out_buf, rand_below(afl, temp_len << 3));
           break;
 
-        case 1:
+        }
+
+        case 4 ... 7: {
 
           /* Set byte to interesting value. */
 
@@ -2092,14 +2097,14 @@ havoc_stage:
               interesting_8[rand_below(afl, sizeof(interesting_8))];
           break;
 
-        case 2:
+        }
+
+        case 8 ... 9: {
 
           /* Set word to interesting value, randomly choosing endian. */
 
           if (temp_len < 2) { break; }
 
-          if (rand_below(afl, 2)) {
-
 #ifdef INTROSPECTION
           snprintf(afl->m_tmp, sizeof(afl->m_tmp), " INTERESTING16");
           strcat(afl->mutation, afl->m_tmp);
@@ -2107,7 +2112,15 @@ havoc_stage:
           *(u16 *)(out_buf + rand_below(afl, temp_len - 1)) =
               interesting_16[rand_below(afl, sizeof(interesting_16) >> 1)];
 
-          } else {
+          break;
+
+        }
+
+        case 10 ... 11: {
+
+          /* Set word to interesting value, randomly choosing endian. */
+
+          if (temp_len < 2) { break; }
 
 #ifdef INTROSPECTION
           snprintf(afl->m_tmp, sizeof(afl->m_tmp), " INTERESTING16BE");
@@ -2116,18 +2129,16 @@ havoc_stage:
           *(u16 *)(out_buf + rand_below(afl, temp_len - 1)) = SWAP16(
               interesting_16[rand_below(afl, sizeof(interesting_16) >> 1)]);
 
-          }
-
           break;
 
-        case 3:
+        }
+
+        case 12 ... 13: {
 
           /* Set dword to interesting value, randomly choosing endian. */
 
           if (temp_len < 4) { break; }
 
-          if (rand_below(afl, 2)) {
-
 #ifdef INTROSPECTION
           snprintf(afl->m_tmp, sizeof(afl->m_tmp), " INTERESTING32");
           strcat(afl->mutation, afl->m_tmp);
@@ -2135,7 +2146,15 @@ havoc_stage:
           *(u32 *)(out_buf + rand_below(afl, temp_len - 3)) =
               interesting_32[rand_below(afl, sizeof(interesting_32) >> 2)];
 
-          } else {
+          break;
+
+        }
+
+        case 14 ... 15: {
+
+          /* Set dword to interesting value, randomly choosing endian. */
+
+          if (temp_len < 4) { break; }
 
 #ifdef INTROSPECTION
           snprintf(afl->m_tmp, sizeof(afl->m_tmp), " INTERESTING32BE");
@@ -2144,11 +2163,11 @@ havoc_stage:
           *(u32 *)(out_buf + rand_below(afl, temp_len - 3)) = SWAP32(
               interesting_32[rand_below(afl, sizeof(interesting_32) >> 2)]);
 
-          }
-
           break;
 
-        case 4:
+        }
+
+        case 16 ... 19: {
 
           /* Randomly subtract from byte. */
 
@@ -2159,7 +2178,9 @@ havoc_stage:
           out_buf[rand_below(afl, temp_len)] -= 1 + rand_below(afl, ARITH_MAX);
           break;
 
-        case 5:
+        }
+
+        case 20 ... 23: {
 
           /* Randomly add to byte. */
 
@@ -2170,14 +2191,14 @@ havoc_stage:
           out_buf[rand_below(afl, temp_len)] += 1 + rand_below(afl, ARITH_MAX);
           break;
 
-        case 6:
+        }
 
-          /* Randomly subtract from word, random endian. */
+        case 24 ... 25: {
+
+          /* Randomly subtract from word, little endian. */
 
           if (temp_len < 2) { break; }
 
-          if (rand_below(afl, 2)) {
-
           u32 pos = rand_below(afl, temp_len - 1);
 
 #ifdef INTROSPECTION
@@ -2186,7 +2207,15 @@ havoc_stage:
 #endif
           *(u16 *)(out_buf + pos) -= 1 + rand_below(afl, ARITH_MAX);
 
-          } else {
+          break;
+
+        }
+
+        case 26 ... 27: {
+
+          /* Randomly subtract from word, big endian. */
+
+          if (temp_len < 2) { break; }
 
           u32 pos = rand_below(afl, temp_len - 1);
           u16 num = 1 + rand_below(afl, ARITH_MAX);
@@ -2199,18 +2228,16 @@ havoc_stage:
           *(u16 *)(out_buf + pos) =
               SWAP16(SWAP16(*(u16 *)(out_buf + pos)) - num);
 
-          }
-
           break;
 
-        case 7:
+        }
 
-          /* Randomly add to word, random endian. */
+        case 28 ... 29: {
+
+          /* Randomly add to word, little endian. */
 
           if (temp_len < 2) { break; }
 
-          if (rand_below(afl, 2)) {
-
           u32 pos = rand_below(afl, temp_len - 1);
 
 #ifdef INTROSPECTION
@@ -2219,7 +2246,15 @@ havoc_stage:
 #endif
           *(u16 *)(out_buf + pos) += 1 + rand_below(afl, ARITH_MAX);
 
-          } else {
+          break;
+
+        }
+
+        case 30 ... 31: {
+
+          /* Randomly add to word, big endian. */
+
+          if (temp_len < 2) { break; }
 
           u32 pos = rand_below(afl, temp_len - 1);
           u16 num = 1 + rand_below(afl, ARITH_MAX);
@@ -2232,18 +2267,16 @@ havoc_stage:
           *(u16 *)(out_buf + pos) =
               SWAP16(SWAP16(*(u16 *)(out_buf + pos)) + num);
 
-          }
-
           break;
 
-        case 8:
+        }
 
-          /* Randomly subtract from dword, random endian. */
+        case 32 ... 33: {
+
+          /* Randomly subtract from dword, little endian. */
 
           if (temp_len < 4) { break; }
 
-          if (rand_below(afl, 2)) {
-
           u32 pos = rand_below(afl, temp_len - 3);
 
 #ifdef INTROSPECTION
@@ -2252,7 +2285,15 @@ havoc_stage:
 #endif
           *(u32 *)(out_buf + pos) -= 1 + rand_below(afl, ARITH_MAX);
 
-          } else {
+          break;
+
+        }
+
+        case 34 ... 35: {
+
+          /* Randomly subtract from dword, big endian. */
+
+          if (temp_len < 4) { break; }
 
           u32 pos = rand_below(afl, temp_len - 3);
           u32 num = 1 + rand_below(afl, ARITH_MAX);
@@ -2265,18 +2306,16 @@ havoc_stage:
           *(u32 *)(out_buf + pos) =
               SWAP32(SWAP32(*(u32 *)(out_buf + pos)) - num);
 
-          }
-
           break;
 
-        case 9:
+        }
 
-          /* Randomly add to dword, random endian. */
+        case 36 ... 37: {
+
+          /* Randomly add to dword, little endian. */
 
           if (temp_len < 4) { break; }
 
-          if (rand_below(afl, 2)) {
-
           u32 pos = rand_below(afl, temp_len - 3);
 
 #ifdef INTROSPECTION
@@ -2285,7 +2324,15 @@ havoc_stage:
 #endif
           *(u32 *)(out_buf + pos) += 1 + rand_below(afl, ARITH_MAX);
 
-          } else {
+          break;
+
+        }
+
+        case 38 ... 39: {
+
+          /* Randomly add to dword, big endian. */
+
+          if (temp_len < 4) { break; }
 
           u32 pos = rand_below(afl, temp_len - 3);
           u32 num = 1 + rand_below(afl, ARITH_MAX);
@@ -2298,11 +2345,11 @@ havoc_stage:
           *(u32 *)(out_buf + pos) =
               SWAP32(SWAP32(*(u32 *)(out_buf + pos)) + num);
 
-          }
-
           break;
 
-        case 10:
+        }
+
+        case 40 ... 43: {
 
           /* Just set a random byte to a random value. Because,
              why not. We use XOR with 1-255 to eliminate the
@@ -2315,21 +2362,155 @@ havoc_stage:
           out_buf[rand_below(afl, temp_len)] ^= 1 + rand_below(afl, 255);
           break;
 
-        case 11 ... 12: {
+        }
+
+        case 44 ... 46: {
+
+          if (temp_len + HAVOC_BLK_XL < MAX_FILE) {
+
+            /* Clone bytes. */
+
+            u32 clone_len = choose_block_len(afl, temp_len);
+            u32 clone_from = rand_below(afl, temp_len - clone_len + 1);
+            u32 clone_to = rand_below(afl, temp_len);
+
+#ifdef INTROSPECTION
+            snprintf(afl->m_tmp, sizeof(afl->m_tmp), " CLONE-%s-%u-%u-%u",
+                     actually_clone ? "clone" : "insert", clone_from, clone_to,
+                     clone_len);
+            strcat(afl->mutation, afl->m_tmp);
+#endif
+            u8 *new_buf =
+                afl_realloc(AFL_BUF_PARAM(out_scratch), temp_len + clone_len);
+            if (unlikely(!new_buf)) { PFATAL("alloc"); }
+
+            /* Head */
+
+            memcpy(new_buf, out_buf, clone_to);
+
+            /* Inserted part */
+
+            memcpy(new_buf + clone_to, out_buf + clone_from, clone_len);
+
+            /* Tail */
+            memcpy(new_buf + clone_to + clone_len, out_buf + clone_to,
+                   temp_len - clone_to);
+
+            out_buf = new_buf;
+            afl_swap_bufs(AFL_BUF_PARAM(out), AFL_BUF_PARAM(out_scratch));
+            temp_len += clone_len;
+
+          }
+
+          break;
+
+        }
+
+        case 47: {
+
+          if (temp_len + HAVOC_BLK_XL < MAX_FILE) {
+
+            /* Insert a block of constant bytes (25%). */
+
+            u32 clone_len = choose_block_len(afl, HAVOC_BLK_XL);
+            u32 clone_to = rand_below(afl, temp_len);
+
+#ifdef INTROSPECTION
+            snprintf(afl->m_tmp, sizeof(afl->m_tmp), " CLONE-%s-%u-%u-%u",
+                     actually_clone ? "clone" : "insert", clone_from, clone_to,
+                     clone_len);
+            strcat(afl->mutation, afl->m_tmp);
+#endif
+            u8 *new_buf =
+                afl_realloc(AFL_BUF_PARAM(out_scratch), temp_len + clone_len);
+            if (unlikely(!new_buf)) { PFATAL("alloc"); }
+
+            /* Head */
+
+            memcpy(new_buf, out_buf, clone_to);
+
+            /* Inserted part */
+
+            memset(new_buf + clone_to,
+                   rand_below(afl, 2) ? rand_below(afl, 256)
+                                      : out_buf[rand_below(afl, temp_len)],
+                   clone_len);
+
+            /* Tail */
+            memcpy(new_buf + clone_to + clone_len, out_buf + clone_to,
+                   temp_len - clone_to);
+
+            out_buf = new_buf;
+            afl_swap_bufs(AFL_BUF_PARAM(out), AFL_BUF_PARAM(out_scratch));
+            temp_len += clone_len;
+
+          }
+
+          break;
+
+        }
+
+        case 48 ... 50: {
+
+          /* Overwrite bytes with a randomly selected chunk bytes. */
+
+          if (temp_len < 2) { break; }
+
+          u32 copy_len = choose_block_len(afl, temp_len - 1);
+          u32 copy_from = rand_below(afl, temp_len - copy_len + 1);
+          u32 copy_to = rand_below(afl, temp_len - copy_len + 1);
+
+          if (likely(copy_from != copy_to)) {
+
+#ifdef INTROSPECTION
+            snprintf(afl->m_tmp, sizeof(afl->m_tmp), " OVERWRITE_COPY-%u-%u-%u",
+                     copy_from, copy_to, copy_len);
+            strcat(afl->mutation, afl->m_tmp);
+#endif
+            memmove(out_buf + copy_to, out_buf + copy_from, copy_len);
+
+          }
+
+          break;
+
+        }
+
+        case 51: {
+
+          /* Overwrite bytes with fixed bytes. */
+
+          if (temp_len < 2) { break; }
+
+          u32 copy_len = choose_block_len(afl, temp_len - 1);
+          u32 copy_to = rand_below(afl, temp_len - copy_len + 1);
+
+#ifdef INTROSPECTION
+          snprintf(afl->m_tmp, sizeof(afl->m_tmp), " OVERWRITE_FIXED-%u-%u-%u",
+                   copy_from, copy_to, copy_len);
+          strcat(afl->mutation, afl->m_tmp);
+#endif
+          memset(out_buf + copy_to,
+                 rand_below(afl, 2) ? rand_below(afl, 256)
+                                    : out_buf[rand_below(afl, temp_len)],
+                 copy_len);
+
+          break;
+
+        }
+
+        // increase from 4 up to 8?
+        case 52 ... MAX_HAVOC_ENTRY: {
 
           /* Delete bytes. We're making this a bit more likely
              than insertion (the next option) in hopes of keeping
              files reasonably small. */
 
-          u32 del_from, del_len;
-
           if (temp_len < 2) { break; }
 
           /* Don't delete too much. */
 
-          del_len = choose_block_len(afl, temp_len - 1);
+          u32 del_len = choose_block_len(afl, temp_len - 1);
-
+          u32 del_from = rand_below(afl, temp_len - del_len + 1);
-          del_from = rand_below(afl, temp_len - del_len + 1);
 
 #ifdef INTROSPECTION
           snprintf(afl->m_tmp, sizeof(afl->m_tmp), " DEL-%u-%u", del_from,
@@ -2345,151 +2526,15 @@ havoc_stage:
 
         }
 
-        case 13:
-
-          if (temp_len + HAVOC_BLK_XL < MAX_FILE) {
-
-            /* Clone bytes (75%) or insert a block of constant bytes (25%). */
-
-            u8  actually_clone = rand_below(afl, 4);
-            u32 clone_from, clone_to, clone_len;
-            u8 *new_buf;
-
-            if (likely(actually_clone)) {
-
-              clone_len = choose_block_len(afl, temp_len);
-              clone_from = rand_below(afl, temp_len - clone_len + 1);
-
-            } else {
-
-              clone_len = choose_block_len(afl, HAVOC_BLK_XL);
-              clone_from = 0;
-
-            }
-
-            clone_to = rand_below(afl, temp_len);
-
-#ifdef INTROSPECTION
-            snprintf(afl->m_tmp, sizeof(afl->m_tmp), " CLONE-%s-%u-%u-%u",
-                     actually_clone ? "clone" : "insert", clone_from, clone_to,
-                     clone_len);
-            strcat(afl->mutation, afl->m_tmp);
-#endif
-            new_buf =
-                afl_realloc(AFL_BUF_PARAM(out_scratch), temp_len + clone_len);
-            if (unlikely(!new_buf)) { PFATAL("alloc"); }
-
-            /* Head */
-
-            memcpy(new_buf, out_buf, clone_to);
-
-            /* Inserted part */
-
-            if (likely(actually_clone)) {
-
-              memcpy(new_buf + clone_to, out_buf + clone_from, clone_len);
-
-            } else {
-
-              memset(new_buf + clone_to,
-                     rand_below(afl, 2) ? rand_below(afl, 256)
-                                        : out_buf[rand_below(afl, temp_len)],
-                     clone_len);
-
-            }
-
-            /* Tail */
-            memcpy(new_buf + clone_to + clone_len, out_buf + clone_to,
-                   temp_len - clone_to);
-
-            out_buf = new_buf;
-            afl_swap_bufs(AFL_BUF_PARAM(out), AFL_BUF_PARAM(out_scratch));
-            temp_len += clone_len;
-
-          }
-
-          break;
-
-        case 14: {
-
-          /* Overwrite bytes with a randomly selected chunk (75%) or fixed
-             bytes (25%). */
-
-          u32 copy_from, copy_to, copy_len;
-
-          if (temp_len < 2) { break; }
-
-          copy_len = choose_block_len(afl, temp_len - 1);
-
-          copy_from = rand_below(afl, temp_len - copy_len + 1);
-          copy_to = rand_below(afl, temp_len - copy_len + 1);
-
-          if (likely(rand_below(afl, 4))) {
-
-            if (likely(copy_from != copy_to)) {
-
-#ifdef INTROSPECTION
-              snprintf(afl->m_tmp, sizeof(afl->m_tmp),
-                       " OVERWRITE_COPY-%u-%u-%u", copy_from, copy_to,
-                       copy_len);
-              strcat(afl->mutation, afl->m_tmp);
-#endif
-              memmove(out_buf + copy_to, out_buf + copy_from, copy_len);
-
-            }
-
-          } else {
-
-#ifdef INTROSPECTION
-            snprintf(afl->m_tmp, sizeof(afl->m_tmp),
-                     " OVERWRITE_FIXED-%u-%u-%u", copy_from, copy_to, copy_len);
-            strcat(afl->mutation, afl->m_tmp);
-#endif
-            memset(out_buf + copy_to,
-                   rand_below(afl, 2) ? rand_below(afl, 256)
-                                      : out_buf[rand_below(afl, temp_len)],
-                   copy_len);
-
-          }
-
-          break;
-
-        }
-
         default:
 
-          if (likely(r <= 16 && (afl->extras_cnt || afl->a_extras_cnt))) {
+          r -= (MAX_HAVOC_ENTRY + 1);
 
-            /* Values 15 and 16 can be selected only if there are any extras
+          if (afl->extras_cnt) {
-               present in the dictionaries. */
 
-            if (r == 15) {
+            if (r < 2) {
 
-              /* Overwrite bytes with an extra. */
+              /* Use the dictionary. */
-
-              if (!afl->extras_cnt ||
-                  (afl->a_extras_cnt && rand_below(afl, 2))) {
-
-                /* No user-specified extras or odds in our favor. Let's use an
-                   auto-detected one. */
-
-                u32 use_extra = rand_below(afl, afl->a_extras_cnt);
-                u32 extra_len = afl->a_extras[use_extra].len;
-
-                if (extra_len > temp_len) { break; }
-
-                u32 insert_at = rand_below(afl, temp_len - extra_len + 1);
-#ifdef INTROSPECTION
-                snprintf(afl->m_tmp, sizeof(afl->m_tmp),
-                         " AUTO_EXTRA_OVERWRITE-%u-%u", insert_at, extra_len);
-                strcat(afl->mutation, afl->m_tmp);
-#endif
-                memcpy(out_buf + insert_at, afl->a_extras[use_extra].data,
-                       extra_len);
-
-              } else {
-
-                /* No auto extras or odds in our favor. Use the dictionary. */
 
               u32 use_extra = rand_below(afl, afl->extras_cnt);
               u32 extra_len = afl->extras[use_extra].len;
@@ -2498,53 +2543,29 @@ havoc_stage:
 
               u32 insert_at = rand_below(afl, temp_len - extra_len + 1);
 #ifdef INTROSPECTION
-                snprintf(afl->m_tmp, sizeof(afl->m_tmp),
+              snprintf(afl->m_tmp, sizeof(afl->m_tmp), " EXTRA_OVERWRITE-%u-%u",
-                         " EXTRA_OVERWRITE-%u-%u", insert_at, extra_len);
+                       insert_at, extra_len);
               strcat(afl->mutation, afl->m_tmp);
 #endif
               memcpy(out_buf + insert_at, afl->extras[use_extra].data,
                      extra_len);
 
-              }
-
               break;
 
-            } else {  // case 16
+            } else if (r < 4) {
 
-              u32 use_extra, extra_len,
+              u32 use_extra = rand_below(afl, afl->extras_cnt);
-                  insert_at = rand_below(afl, temp_len + 1);
+              u32 extra_len = afl->extras[use_extra].len;
-              u8 *ptr;
+              if (temp_len + extra_len >= MAX_FILE) { break; }
 
-              /* Insert an extra. Do the same dice-rolling stuff as for the
+              u8 *ptr = afl->extras[use_extra].data;
-                 previous case. */
+              u32 insert_at = rand_below(afl, temp_len + 1);
-
-              if (!afl->extras_cnt ||
-                  (afl->a_extras_cnt && rand_below(afl, 2))) {
-
-                use_extra = rand_below(afl, afl->a_extras_cnt);
-                extra_len = afl->a_extras[use_extra].len;
-                ptr = afl->a_extras[use_extra].data;
-#ifdef INTROSPECTION
-                snprintf(afl->m_tmp, sizeof(afl->m_tmp),
-                         " AUTO_EXTRA_INSERT-%u-%u", insert_at, extra_len);
-                strcat(afl->mutation, afl->m_tmp);
-#endif
-
-              } else {
-
-                use_extra = rand_below(afl, afl->extras_cnt);
-                extra_len = afl->extras[use_extra].len;
-                ptr = afl->extras[use_extra].data;
 #ifdef INTROSPECTION
               snprintf(afl->m_tmp, sizeof(afl->m_tmp), " EXTRA_INSERT-%u-%u",
                        insert_at, extra_len);
               strcat(afl->mutation, afl->m_tmp);
 #endif
 
-              }
-
-              if (temp_len + extra_len >= MAX_FILE) { break; }
-
               out_buf = afl_realloc(AFL_BUF_PARAM(out), temp_len + extra_len);
               if (unlikely(!out_buf)) { PFATAL("alloc"); }
 
@@ -2554,23 +2575,77 @@ havoc_stage:
 
               /* Inserted part */
               memcpy(out_buf + insert_at, ptr, extra_len);
-
               temp_len += extra_len;
 
               break;
 
+            } else {
+
+              r -= 4;
+
             }
 
+          }
+
+          if (afl->a_extras_cnt) {
+
+            if (r == 0) {
+
+              /* Use the dictionary. */
+
+              u32 use_extra = rand_below(afl, afl->a_extras_cnt);
+              u32 extra_len = afl->a_extras[use_extra].len;
+
+              if (extra_len > temp_len) { break; }
+
+              u32 insert_at = rand_below(afl, temp_len - extra_len + 1);
+#ifdef INTROSPECTION
+              snprintf(afl->m_tmp, sizeof(afl->m_tmp), " AUTO_EXTRA_OVERWRITE-%u-%u",
+                       insert_at, extra_len);
+              strcat(afl->mutation, afl->m_tmp);
+#endif
+              memcpy(out_buf + insert_at, afl->a_extras[use_extra].data,
+                     extra_len);
+
+              break;
+
+            } else if (r == 1) {
+
+              u32 use_extra = rand_below(afl, afl->a_extras_cnt);
+              u32 extra_len = afl->a_extras[use_extra].len;
+              if (temp_len + extra_len >= MAX_FILE) { break; }
+
+              u8 *ptr = afl->a_extras[use_extra].data;
+              u32 insert_at = rand_below(afl, temp_len + 1);
+#ifdef INTROSPECTION
+              snprintf(afl->m_tmp, sizeof(afl->m_tmp), " AUTO_EXTRA_INSERT-%u-%u",
+                       insert_at, extra_len);
+              strcat(afl->mutation, afl->m_tmp);
+#endif
+
+              out_buf = afl_realloc(AFL_BUF_PARAM(out), temp_len + extra_len);
+              if (unlikely(!out_buf)) { PFATAL("alloc"); }
+
+              /* Tail */
+              memmove(out_buf + insert_at + extra_len, out_buf + insert_at,
+                      temp_len - insert_at);
+
+              /* Inserted part */
+              memcpy(out_buf + insert_at, ptr, extra_len);
+              temp_len += extra_len;
+
+              break;
+
             } else {
 
-            /*
+              r -= 2;
-                        switch (r) {
 
-                          case 15:  // fall through
+            }
-                          case 16:
-                          case 17: {*/
 
-            /* Overwrite bytes with a randomly selected chunk from another
+          }
+
+          /* Splicing otherwise if we are still here.
+             Overwrite bytes with a randomly selected chunk from another
              testcase or insert that chunk. */
 
           /* Pick a random queue entry and seek to it. */
@@ -2587,8 +2662,7 @@ havoc_stage:
           u32                 new_len = target->len;
           u8 *                new_buf = queue_testcase_get(afl, target);
 
-            if ((temp_len >= 2 && rand_below(afl, 2)) ||
+          if ((temp_len >= 2 && r % 2) || temp_len + HAVOC_BLK_XL >= MAX_FILE) {
-                temp_len + HAVOC_BLK_XL >= MAX_FILE) {
 
             /* overwrite mode */
 
@@ -2648,9 +2722,7 @@ havoc_stage:
 
           break;
 
-          }
+          // end of default
-
-          // end of default:
 
       }