From: Steinar H. Gunderson <sesse@debian.org>
Date: Sat, 3 Jan 2009 13:14:16 +0000 (+0100)
Subject: The bit source needs to actually consume the data it passes by...
X-Git-Url: https://git.sesse.net/?p=fjl;a=commitdiff_plain;h=ddc3c24c837f081787825d128675eca628d0e91c;hp=d5b9f8f45a79e6f25045bcc10511884a20fc8912

The bit source needs to actually consume the data it passes by...
---

diff --git a/bitsource.c b/bitsource.c
index 72b143b..6cc627c 100644
--- a/bitsource.c
+++ b/bitsource.c
@@ -12,15 +12,20 @@ void init_bit_source(struct bit_source* source, input_func_t* input_func, void*
 {
 	memset(source, 0, sizeof(*source));
 	source->bytes = (uint8_t*)malloc(BYTERESERVOIR_SIZE);
+	source->byte_read_ptr = source->bytes;
 	source->input_func = input_func;
 	source->userdata = userdata;
 }
 
 void possibly_refill_slow_path(struct bit_source* source, unsigned num_bits)
 {
-	// First, make sure there's stuff in the byte reservoir if we can.
+	// First, move out the data we already read.
 	assert(source->bytes_available <= BYTERESERVOIR_SIZE);
+	assert(source->byte_read_ptr >= source->bytes);
+	memmove(source->bytes, source->byte_read_ptr, source->bytes_available);
+	source->byte_read_ptr = source->bytes;
 
+	// Then, make sure there's stuff in the byte reservoir if we can.
 	// Read data from the source until we have enough to satisfy the request.
 	while (source->bits_available + 8 * source->bytes_available < num_bits) {
 		const size_t bytes_to_read = BYTERESERVOIR_SIZE - source->bytes_available;
@@ -50,8 +55,8 @@ void possibly_refill_slow_path(struct bit_source* source, unsigned num_bits)
 	while (source->bits_available < num_bits) {
 		assert(source->bytes_available > 0);
 		assert(source->bits_available + 8 <= BITRESERVOIR_SIZE);
-		uint8_t byte = *(source->bytes);
-		++source->bytes;
+		uint8_t byte = *(source->byte_read_ptr);
+		++source->byte_read_ptr;
 		--source->bytes_available;
 		source->bits |= ((bitreservoir_t)byte << (BITRESERVOIR_SIZE - source->bits_available - 8));
 		source->bits_available += 8;
diff --git a/bitsource.h b/bitsource.h
index 6cabbf0..bb3a6d2 100644
--- a/bitsource.h
+++ b/bitsource.h
@@ -34,6 +34,7 @@ struct bit_source {
 	// When this is empty, it needs to be refilled from the input
 	// stream.
 	uint8_t* bytes;
+	uint8_t* byte_read_ptr;
 	unsigned bytes_available;
 
 	// Data source.
@@ -62,8 +63,8 @@ static inline void possibly_refill(struct bit_source* source, unsigned num_bits)
 	// Slower path (~99% of remaining invocations?)
 	assert(source->bits_available + BITRESERVOIR_FILL_SIZE < BITRESERVOIR_SIZE);
 	if (source->bytes_available >= sizeof(bitreservoir_fill_t)) {
-		bitreservoir_fill_t fill = read_bitreservoir_fill(source->bytes);
-		source->bytes += sizeof(bitreservoir_fill_t);
+		bitreservoir_fill_t fill = read_bitreservoir_fill(source->byte_read_ptr);
+		source->byte_read_ptr += sizeof(bitreservoir_fill_t);
 		source->bytes_available -= sizeof(bitreservoir_fill_t);
 		source->bits |= (bitreservoir_t)fill << (BITRESERVOIR_SIZE - BITRESERVOIR_FILL_SIZE - source->bits_available);
 		source->bits_available += BITRESERVOIR_FILL_SIZE;