From 5c7dde620c0cd365b257f1f1286872aafcee8078 Mon Sep 17 00:00:00 2001
From: Philip Heron <phil@sanslogic.co.uk>
Date: Wed, 27 Jun 2018 08:45:07 +0100
Subject: [PATCH] Fix image corruption bug where the DC levels where not being
 reset correctly on decoding

---
 ssdv.c | 18 ++++++++++++++----
 ssdv.h |  1 +
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/ssdv.c b/ssdv.c
index 7817e39..757a208 100644
--- a/ssdv.c
+++ b/ssdv.c
@@ -588,6 +588,7 @@ static char ssdv_process(ssdv_t *s)
 		{
 			s->mcupart = 0;
 			s->mcu_id++;
+			s->reset_mcu = s->next_reset_mcu;
 			
 			/* Test for the end of image */
 			if(s->mcu_id >= s->mcu_count)
@@ -603,13 +604,15 @@ static char ssdv_process(ssdv_t *s)
 				/* The first MCU of each packet should be byte aligned */
 				ssdv_outbits_sync(s);
 				
-				s->reset_mcu = s->mcu_id;
+				s->next_reset_mcu = s->reset_mcu = s->mcu_id;
 				s->packet_mcu_id = s->mcu_id;
 				s->packet_mcu_offset = s->pkt_size_payload - s->out_len;
 			}
 			
 			if(s->mode == S_DECODING && s->mcu_id == s->reset_mcu)
+			{
 				s->workbits = s->worklen = 0;
+			}
 			
 			/* Test for a reset marker */
 			if(s->dri > 0 && s->mcu_id > 0 && s->mcu_id % s->dri == 0)
@@ -1028,9 +1031,10 @@ char ssdv_enc_get_packet(ssdv_t *s)
 			
 			if(r == SSDV_BUFFER_FULL || r == SSDV_EOI)
 			{
-				uint16_t mcu_id     = s->packet_mcu_id;
-				uint8_t i, mcu_offset = s->packet_mcu_offset;
+				uint16_t mcu_id    = s->packet_mcu_id;
+				uint8_t mcu_offset = s->packet_mcu_offset;
 				uint32_t x;
+				uint8_t i;
 				
 				if(mcu_offset != 0xFF && mcu_offset >= s->pkt_size_payload)
 				{
@@ -1251,7 +1255,13 @@ char ssdv_dec_feed(ssdv_t *s, uint8_t *packet)
 	s->packet_mcu_offset = packet[12];
 	s->packet_mcu_id     = (packet[13] << 8) | packet[14];
 	
-	if(s->packet_mcu_id != 0xFFFF) s->reset_mcu = s->packet_mcu_id;
+	if(s->packet_mcu_id != 0xFFFF)
+	{
+		/* Set the next reset MCU ID. We can't set it
+		 * directly here as the previous MCU may still
+		 * be being processed. */
+		s->next_reset_mcu = s->packet_mcu_id;
+	}
 	
 	/* If this is the first packet, write the JPEG headers */
 	if(s->packet_id == 0)
diff --git a/ssdv.h b/ssdv.h
index 0b9393c..a536562 100644
--- a/ssdv.h
+++ b/ssdv.h
@@ -114,6 +114,7 @@ typedef struct
 		S_DECODING,
 	} mode;
 	uint32_t reset_mcu; /* MCU block to do absolute encoding            */
+	uint32_t next_reset_mcu;
 	char needbits;      /* Number of bits needed to decode integer      */
 	
 	/* The input huffman and quantisation tables */