First Commit

3rdparty/libchdr/src/libchdr_bitstream.c

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+/* license:BSD-3-Clause
+ * copyright-holders:Aaron Giles
+***************************************************************************
+
+    bitstream.c
+
+    Helper classes for reading/writing at the bit level.
+
+***************************************************************************/
+
+#include <stdlib.h>
+#include <libchdr/bitstream.h>
+
+/***************************************************************************
+ *  INLINE FUNCTIONS
+ ***************************************************************************
+ */
+
+int bitstream_overflow(struct bitstream* bitstream) { return ((bitstream->doffset - bitstream->bits / 8) > bitstream->dlength); }
+
+/*-------------------------------------------------
+ *  create_bitstream - constructor
+ *-------------------------------------------------
+ */
+
+struct bitstream* create_bitstream(const void *src, uint32_t srclength)
+{
+	struct bitstream* bitstream = (struct bitstream*)malloc(sizeof(struct bitstream));
+	bitstream->buffer = 0;
+	bitstream->bits = 0;
+	bitstream->read = (const uint8_t*)src;
+	bitstream->doffset = 0;
+	bitstream->dlength = srclength;
+	return bitstream;
+}
+
+
+/*-----------------------------------------------------
+ *  bitstream_peek - fetch the requested number of bits
+ *  but don't advance the input pointer
+ *-----------------------------------------------------
+ */
+
+uint32_t bitstream_peek(struct bitstream* bitstream, int numbits)
+{
+	if (numbits == 0)
+		return 0;
+
+	/* fetch data if we need more */
+	if (numbits > bitstream->bits)
+	{
+		while (bitstream->bits <= 24)
+		{
+			if (bitstream->doffset < bitstream->dlength)
+				bitstream->buffer |= bitstream->read[bitstream->doffset] << (24 - bitstream->bits);
+			bitstream->doffset++;
+			bitstream->bits += 8;
+		}
+	}
+
+	/* return the data */
+	return bitstream->buffer >> (32 - numbits);
+}
+
+
+/*-----------------------------------------------------
+ *  bitstream_remove - advance the input pointer by the
+ *  specified number of bits
+ *-----------------------------------------------------
+ */
+
+void bitstream_remove(struct bitstream* bitstream, int numbits)
+{
+	bitstream->buffer <<= numbits;
+	bitstream->bits -= numbits;
+}
+
+
+/*-----------------------------------------------------
+ *  bitstream_read - fetch the requested number of bits
+ *-----------------------------------------------------
+ */
+
+uint32_t bitstream_read(struct bitstream* bitstream, int numbits)
+{
+	uint32_t result = bitstream_peek(bitstream, numbits);
+	bitstream_remove(bitstream, numbits);
+	return result;
+}
+
+
+/*-------------------------------------------------
+ *  read_offset - return the current read offset
+ *-------------------------------------------------
+ */
+
+uint32_t bitstream_read_offset(struct bitstream* bitstream)
+{
+	uint32_t result = bitstream->doffset;
+	int bits = bitstream->bits;
+	while (bits >= 8)
+	{
+		result--;
+		bits -= 8;
+	}
+	return result;
+}
+
+
+/*-------------------------------------------------
+ *  flush - flush to the nearest byte
+ *-------------------------------------------------
+ */
+
+uint32_t bitstream_flush(struct bitstream* bitstream)
+{
+	while (bitstream->bits >= 8)
+	{
+		bitstream->doffset--;
+		bitstream->bits -= 8;
+	}
+	bitstream->bits = bitstream->buffer = 0;
+	return bitstream->doffset;
+}
+