From 5108c9ac975b5e4ff62418584cc6c8934d747b38 Mon Sep 17 00:00:00 2001 From: Yann Collet Date: Sat, 27 May 2023 11:22:30 -0700 Subject: [PATCH] Fixed a bug in the educational decoder Credit to Igor Pavlov --- doc/educational_decoder/zstd_decompress.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/doc/educational_decoder/zstd_decompress.c b/doc/educational_decoder/zstd_decompress.c index 3196b78dc38..1da7c528d23 100644 --- a/doc/educational_decoder/zstd_decompress.c +++ b/doc/educational_decoder/zstd_decompress.c @@ -997,7 +997,8 @@ static void decompress_sequences(frame_context_t *const ctx, const size_t num_sequences); static sequence_command_t decode_sequence(sequence_states_t *const state, const u8 *const src, - i64 *const offset); + i64 *const offset, + int lastSequence); static void decode_seq_table(FSE_dtable *const table, istream_t *const in, const seq_part_t type, const seq_mode_t mode); @@ -1114,7 +1115,7 @@ static void decompress_sequences(frame_context_t *const ctx, istream_t *in, for (size_t i = 0; i < num_sequences; i++) { // Decode sequences one by one - sequences[i] = decode_sequence(&states, src, &bit_offset); + sequences[i] = decode_sequence(&states, src, &bit_offset, i==num_sequences-1); } if (bit_offset != 0) { @@ -1125,7 +1126,8 @@ static void decompress_sequences(frame_context_t *const ctx, istream_t *in, // Decode a single sequence and update the state static sequence_command_t decode_sequence(sequence_states_t *const states, const u8 *const src, - i64 *const offset) { + i64 *const offset, + int lastSequence) { // "Each symbol is a code in its own context, which specifies Baseline and // Number_of_Bits to add. Codes are FSE compressed, and interleaved with raw // additional bits in the same bitstream." @@ -1160,7 +1162,7 @@ static sequence_command_t decode_sequence(sequence_states_t *const states, // Literals_Length_State is updated, followed by Match_Length_State, and // then Offset_State." // If the stream is complete don't read bits to update state - if (*offset != 0) { + if (!lastSequence) { FSE_update_state(&states->ll_table, &states->ll_state, src, offset); FSE_update_state(&states->ml_table, &states->ml_state, src, offset); FSE_update_state(&states->of_table, &states->of_state, src, offset);