Clarify that a non-zero probability for an invalid symbol is invalid

diff --git a/doc/zstd_compression_format.md b/doc/zstd_compression_format.md
index 0532a846f45ceacbb7cfe86b24b42e4aa465990c..216d89ed150c4cf253955480e53f54c7457fae05 100644 (file)
--- a/doc/zstd_compression_format.md
+++ b/doc/zstd_compression_format.md
@@ -1124,6 +1124,9 @@ When last symbol reaches cumulated total of `1 << Accuracy_Log`,
 decoding is complete.
 If the last symbol makes cumulated total go above `1 << Accuracy_Log`,
 distribution is considered corrupted.
+If this process results in a non-zero probability for a value outside of the
+valid range of values that the FSE table is defined for, even if that value is
+not used, then the data is considered corrupted.
 
 Then the decoder can tell how many bytes were used in this process,
 and how many symbols are present.