1 files changed, 105 insertions, 0 deletions
diff --git a/src/lzw.h b/src/lzw.h
new file mode 100644
index 0000000..385b425
--- /dev/null
+++ b/src/lzw.h
@@ -0,0 +1,105 @@
+/*
+ * This file is part of NetSurf's LibNSGIF, http://www.netsurf-browser.org/
+ * Licensed under the MIT License,
+ *                http://www.opensource.org/licenses/mit-license.php
+ *
+ * Copyright 2017 Michael Drake <michael.drake@codethink.co.uk>
+ */
+
+#ifndef LZW_H_
+#define LZW_H_
+
+/**
+ * \file
+ * \brief LZW decompression (interface)
+ *
+ * Decoder for GIF LZW data.
+ */
+
+
+/** Maximum LZW code size in bits */
+#define LZW_CODE_MAX 12
+
+
+/* Declare lzw internal context structure */
+struct lzw_ctx;
+
+
+/** LZW decoding response codes */
+typedef enum lzw_result {
+	LZW_OK,        /**< Success */
+	LZW_OK_EOD,    /**< Success; reached zero-length sub-block */
+	LZW_NO_MEM,    /**< Error: Out of memory */
+	LZW_NO_DATA,   /**< Error: Out of data */
+	LZW_EOI_CODE,  /**< Error: End of Information code */
+	LZW_BAD_ICODE, /**< Error: Bad initial LZW code */
+	LZW_BAD_CODE,  /**< Error: Bad LZW code */
+} lzw_result;
+
+
+/**
+ * Create an LZW decompression context.
+ *
+ * \param[out] ctx  Returns an LZW decompression context.  Caller owned,
+ *                  free with lzw_context_destroy().
+ * \return LZW_OK on success, or appropriate error code otherwise.
+ */
+lzw_result lzw_context_create(
+		struct lzw_ctx **ctx);
+
+/**
+ * Destroy an LZW decompression context.
+ *
+ * \param[in] ctx  The LZW decompression context to destroy.
+ */
+void lzw_context_destroy(
+		struct lzw_ctx *ctx);
+
+/**
+ * Initialise an LZW decompression context for decoding.
+ *
+ * Caller owns neither `stack_base_out` or `stack_pos_out`.
+ *
+ * \param[in]  ctx                  The LZW decompression context to initialise.
+ * \param[in]  compressed_data      The compressed data.
+ * \param[in]  compressed_data_len  Byte length of compressed data.
+ * \param[in]  compressed_data_pos  Start position in data.  Must be position
+ *                                  of a size byte at sub-block start.
+ * \param[in]  code_size            The initial LZW code size to use.
+ * \param[out] stack_base_out       Returns base of decompressed data stack.
+ * \param[out] stack_pos_out        Returns current stack position.
+ *                                  There are `stack_pos_out - stack_base_out`
+ *                                  current stack entries.
+ * \return LZW_OK on success, or appropriate error code otherwise.
+ */
+lzw_result lzw_decode_init(
+		struct lzw_ctx *ctx,
+		const uint8_t *compressed_data,
+		uint32_t compressed_data_len,
+		uint32_t compressed_data_pos,
+		uint8_t code_size,
+		const uint8_t ** const stack_base_out,
+		const uint8_t ** const stack_pos_out);
+
+/**
+ * Fill the LZW stack with decompressed data
+ *
+ * Ensure anything on the stack is used before calling this, as anything
+ * on the stack before this call will be trampled.
+ *
+ * Caller does not own `stack_pos_out`.
+ *
+ * \param[in]  ctx            LZW reading context, updated.
+ * \param[out] stack_pos_out  Returns current stack position.
+ *                            Use with `stack_base_out` value from previous
+ *                            lzw_decode_init() call.
+ *                            There are `stack_pos_out - stack_base_out`
+ *                            current stack entries.
+ * \return LZW_OK on success, or appropriate error code otherwise.
+ */
+lzw_result lzw_decode(
+		struct lzw_ctx *ctx,
+		const uint8_t ** const stack_pos_out);
+
+
+#endif