1 files changed, 100 insertions, 0 deletions
diff --git a/tests/fuzz/fse_read_ncount.c b/tests/fuzz/fse_read_ncount.c
new file mode 100644
index 00000000..e20a9382
--- /dev/null
+++ b/tests/fuzz/fse_read_ncount.c
@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2016-2020, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under both the BSD-style license (found in the
+ * LICENSE file in the root directory of this source tree) and the GPLv2 (found
+ * in the COPYING file in the root directory of this source tree).
+ * You may select, at your option, one of the above-listed licenses.
+ */
+
+/**
+ * This fuzz target round trips the FSE normalized count with FSE_writeNCount()
+ * and FSE_readNcount() to ensure that it can always round trip correctly.
+ */
+
+#define FSE_STATIC_LINKING_ONLY
+#define ZSTD_STATIC_LINKING_ONLY
+
+#include <stddef.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include "fuzz_helpers.h"
+#include "zstd_helpers.h"
+#include "fuzz_data_producer.h"
+#include "fse.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *src, size_t size)
+{
+    FUZZ_dataProducer_t *producer = FUZZ_dataProducer_create(src, size);
+
+    /* Pick a random tableLog and maxSymbolValue */
+    unsigned const tableLog = FUZZ_dataProducer_uint32Range(producer, FSE_MIN_TABLELOG, FSE_MAX_TABLELOG);
+    unsigned const maxSymbolValue = FUZZ_dataProducer_uint32Range(producer, 0, 255);
+
+    unsigned remainingWeight = (1u << tableLog) - 1;
+    size_t dataSize;
+    BYTE data[512];
+    short ncount[256];
+
+    /* Randomly fill the normalized count */
+    memset(ncount, 0, sizeof(ncount));
+    {
+        unsigned s;
+        for (s = 0; s < maxSymbolValue && remainingWeight > 0; ++s) {
+            short n = (short)FUZZ_dataProducer_int32Range(producer, -1, remainingWeight);
+            ncount[s] = n;
+            if (n < 0) {
+                remainingWeight -= 1;
+            } else {
+                assert((unsigned)n <= remainingWeight);
+                remainingWeight -= n;
+            }
+        }
+        /* Ensure ncount[maxSymbolValue] != 0 and the sum is (1<<tableLog) */
+        ncount[maxSymbolValue] = remainingWeight + 1;
+        if (ncount[maxSymbolValue] == 1 && FUZZ_dataProducer_uint32Range(producer, 0, 1) == 1) {
+            ncount[maxSymbolValue] = -1;
+        }
+    }
+    /* Write the normalized count */
+    {
+        FUZZ_ASSERT(sizeof(data) >= FSE_NCountWriteBound(maxSymbolValue, tableLog));
+        dataSize = FSE_writeNCount(data, sizeof(data), ncount, maxSymbolValue, tableLog);
+        FUZZ_ZASSERT(dataSize);
+    }
+    /* Read & validate the normalized count */
+    {
+        short rtNcount[256];
+        unsigned rtMaxSymbolValue = 255;
+        unsigned rtTableLog;
+        /* Copy into a buffer with a random amount of random data at the end */
+        size_t const buffSize = (size_t)FUZZ_dataProducer_uint32Range(producer, dataSize, sizeof(data));
+        BYTE* const buff = FUZZ_malloc(buffSize);
+        size_t rtDataSize;
+        memcpy(buff, data, dataSize); 
+        {
+            size_t b;
+            for (b = dataSize; b < buffSize; ++b) {
+                buff[b] = (BYTE)FUZZ_dataProducer_uint32Range(producer, 0, 255);
+            }
+        }
+
+        rtDataSize = FSE_readNCount(rtNcount, &rtMaxSymbolValue, &rtTableLog, buff, buffSize);
+        FUZZ_ZASSERT(rtDataSize);
+        FUZZ_ASSERT(rtDataSize == dataSize);
+        FUZZ_ASSERT(rtMaxSymbolValue == maxSymbolValue);
+        FUZZ_ASSERT(rtTableLog == tableLog);
+        {
+            unsigned s;
+            for (s = 0; s <= maxSymbolValue; ++s) {
+                FUZZ_ASSERT(ncount[s] == rtNcount[s]);
+            }
+        }
+        free(buff);
+    }
+
+    FUZZ_dataProducer_free(producer);
+    return 0;
+}