Merge pull request #3398 from facebook/fix3316

spec update : require minimum nb of literals for 4-streams mode

lib/decompress/zstd_decompress_block.c

@@ -166,6 +166,10 @@ size_t ZSTD_decodeLiteralsBlock(ZSTD_DCtx* dctx,
                 }
                 RETURN_ERROR_IF(litSize > 0 && dst == NULL, dstSize_tooSmall, "NULL not handled");
                 RETURN_ERROR_IF(litSize > ZSTD_BLOCKSIZE_MAX, corruption_detected, "");
+                if (!singleStream)
+                    RETURN_ERROR_IF(litSize < MIN_LITERALS_FOR_4_STREAMS, literals_headerWrong,
+                        "Not enough literals (%zu) for the 4-streams mode (min %u)",
+                        litSize, MIN_LITERALS_FOR_4_STREAMS);
                 RETURN_ERROR_IF(litCSize + lhSize > srcSize, corruption_detected, "");
                 RETURN_ERROR_IF(expectedWriteSize < litSize , dstSize_tooSmall, "");
                 ZSTD_allocateLiteralsBuffer(dctx, dst, dstCapacity, litSize, streaming, expectedWriteSize, 0);
@@ -181,6 +185,7 @@ size_t ZSTD_decodeLiteralsBlock(ZSTD_DCtx* dctx,
                             dctx->litBuffer, litSize, istart+lhSize, litCSize,
                             dctx->HUFptr, ZSTD_DCtx_get_bmi2(dctx));
                     } else {
+                        assert(litSize >= MIN_LITERALS_FOR_4_STREAMS);
                         hufSuccess = HUF_decompress4X_usingDTable_bmi2(
                             dctx->litBuffer, litSize, istart+lhSize, litCSize,
                             dctx->HUFptr, ZSTD_DCtx_get_bmi2(dctx));
@@ -509,7 +514,8 @@ void ZSTD_buildFSETable_body(ZSTD_seqSymbol* dt,
                 for (i = 8; i < n; i += 8) {
                     MEM_write64(spread + pos + i, sv);
                 }
-                pos += n;
+                assert(n>=0);
+                pos += (size_t)n;
             }
         }
         /* Now we spread those positions across the table.