diff --git a/lib/keccak/keccak.c b/lib/keccak/keccak.c
index 8f51c1af..a621e665 100644
--- a/lib/keccak/keccak.c
+++ b/lib/keccak/keccak.c
@@ -8,6 +8,7 @@
 #if !__has_builtin(__builtin_memcpy) && !defined(__GNUC__)
 #include <string.h>
 #define __builtin_memcpy memcpy
+#define __builtin_memset memset
 #endif
 
 #if defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
@@ -399,10 +400,10 @@ static inline ALWAYS_INLINE void keccak_update(
     size_t i;
 
     size_t block_size_b = ctx->block_size / word_size;  // block size in bytes
-    size_t last_word_unfilled_size =  // calculate unfilled space in last word, ignore if all empty
-        (word_size - (size_t)(ctx->last_word_iter - (uint8_t*)&(ctx->last_word))) % word_size;
-    size_t state_unfilled_size =  // calculate unfilled space in state, ignore if all empty
-        (block_size_b - (size_t)(ctx->state_iter - ctx->state)) % block_size_b;
+    size_t last_word_unfilled_size =  // calculate unfilled space in last word
+        (word_size - (size_t)(ctx->last_word_iter - (uint8_t*)&(ctx->last_word)));
+    size_t state_unfilled_size =  // calculate unfilled space in state
+        (block_size_b - (size_t)(ctx->state_iter - ctx->state));
 
     // fill the last word unfilled space with bytes until it's full
     while(last_word_unfilled_size > 0 && size > 0)
diff --git a/test/unittests/test_keccak.cpp b/test/unittests/test_keccak.cpp
index 8960ce0e..6a69240e 100644
--- a/test/unittests/test_keccak.cpp
+++ b/test/unittests/test_keccak.cpp
@@ -283,6 +283,25 @@ TEST(helpers, to_hash256_empty)
     EXPECT_EQ(h, hash256{});
 }
 
+static size_t next_data_size_to_load()
+{
+    static size_t next = 1;
+    static const size_t sizes[216]
+        = {225, 50, 73, 72, 285, 273, 139, 299, 193, 243, 43, 102, 294, 262, 209, 114, 88, 94, 179, 233, 248,
+           182, 34, 246, 106, 148, 198, 77, 160, 289, 115, 249, 198, 26, 203, 21, 24, 65, 222, 187, 170, 281,
+           285, 185, 261, 121, 130, 270, 22, 227, 235, 206, 116, 205, 171, 30, 163, 94, 66, 98, 112, 271, 98,
+           91, 181, 181, 145, 290, 12, 261, 183, 82, 40, 25, 40, 164, 293, 150, 96, 195, 218, 122, 240, 99, 7,
+           71, 155, 165, 180, 238, 131, 271, 286, 186, 255, 62, 65, 110, 205, 86, 2, 83, 182, 225, 5, 156, 138,
+           139, 146, 3, 250, 51, 184, 282, 9, 109, 34, 245, 169, 63, 240, 100, 151, 134, 74, 125, 225, 30, 215,
+           199, 275, 131, 128, 89, 37, 195, 286, 220, 117, 183, 32, 132, 51, 122, 244, 104, 59, 73, 45, 188, 115,
+           231, 179, 217, 16, 110, 58, 142, 186, 215, 201, 223, 198, 152, 64, 9, 113, 39, 141, 209, 170, 84, 209,
+           16, 92, 64, 85, 239, 128, 88, 298, 153, 28, 269, 30, 38, 46, 97, 242, 119, 102, 299, 103, 288, 251, 187,
+           192, 8, 57, 293, 221, 43, 184, 207, 50, 129, 203, 45, 139, 0, 129, 82, 285, 254, 214, 213};
+
+    next = (next + 1) % 216;
+    return sizes[next];
+}
+
 TEST(keccak, iuf_test_simple)
 {
     const uint8_t* const data = reinterpret_cast<const uint8_t*>(test_text);
@@ -292,7 +311,7 @@ TEST(keccak, iuf_test_simple)
         const auto h256 = keccak256(data, t.input_size);
         ASSERT_EQ(to_hex(h256), t.expected_hash256) << t.input_size;
 
-        struct ethash_keccak256_context ctx;
+        struct ethash_keccak256_context ctx = {};
         keccak256_init(&ctx);
         keccak256_update(&ctx, data, t.input_size);
         const auto h2561 = keccak256_final(&ctx);
@@ -328,11 +347,11 @@ TEST(keccak, iuf_test_simple)
         i = 0;
         while(i <  t.input_size) 
         {
-            step = (size_t)rand() % 300;
+            step = next_data_size_to_load();
             size_t l = t.input_size - i >= step ? step : t.input_size - i;
             keccak256_update(&ctx, &data[i], l);
             i = i + step;
-        }        
+        }
         const auto h2563 = keccak256_final(&ctx);
         ASSERT_EQ(to_hex(h2563), t.expected_hash256) << t.input_size;
     }
@@ -345,7 +364,7 @@ TEST(keccak, iuf_test_simple_2)
     for (auto& t : test_cases)
     {
         {
-            struct ethash_keccak256_context ctx;
+            struct ethash_keccak256_context ctx = {};
             keccak256_init_2(&ctx);
             keccak256_update_2(&ctx, data, t.input_size);
             const auto h256 = keccak256_final_2(&ctx);
@@ -355,7 +374,7 @@ TEST(keccak, iuf_test_simple_2)
         {
             size_t i;
 
-            struct ethash_keccak256_context ctx;
+            struct ethash_keccak256_context ctx = {};
             keccak256_init_2(&ctx);
             for(i = 0; i <  t.input_size; ++i) 
             {
@@ -368,7 +387,7 @@ TEST(keccak, iuf_test_simple_2)
         {
             size_t i;
             size_t step = 0;
-            struct ethash_keccak256_context ctx;
+            struct ethash_keccak256_context ctx = {};
             for(step = 1; step < 256; ++step) 
             {
                 keccak256_init_2(&ctx);
@@ -384,14 +403,14 @@ TEST(keccak, iuf_test_simple_2)
         }
 
         {
-            struct ethash_keccak256_context ctx;
+            struct ethash_keccak256_context ctx = {};
             keccak256_init_2(&ctx);
             
             size_t i = 0;
             size_t step = 0;
             while(i <  t.input_size) 
             {
-                step = (size_t)rand() % 300;
+                step = next_data_size_to_load();
                 size_t l = t.input_size - i >= step ? step : t.input_size - i;
                 keccak256_update_2(&ctx, &data[i], l);
                 i = i + step;
@@ -400,4 +419,4 @@ TEST(keccak, iuf_test_simple_2)
             ASSERT_EQ(to_hex(h256), t.expected_hash256) << t.input_size;
         }
     }
-}
\ No newline at end of file
+}