+/* Determine if the chunk size is valid for the specified compression type. */
+static bool
+wim_chunk_size_valid(u32 chunk_size, int ctype)
+{
+ u32 order;
+
+ /* Chunk size is meaningless for uncompressed WIMs --- any value is
+ * okay. */
+ if (ctype == WIMLIB_COMPRESSION_TYPE_NONE)
+ return true;
+
+ /* Chunk size must be power of 2. */
+ if (chunk_size == 0)
+ return false;
+ order = bsr32(chunk_size);
+ if (chunk_size != 1U << order)
+ return false;
+
+ /* Order Size
+ * ===== ====
+ * 15 32768
+ * 16 65536
+ * 17 131072
+ * 18 262144
+ * 19 524288
+ * 20 1048576
+ * 21 2097152
+ * 22 4194304
+ * 23 8388608
+ * 24 16777216
+ * 25 33554432
+ * 26 67108864
+ */
+ switch (ctype) {
+ case WIMLIB_COMPRESSION_TYPE_LZX:
+ /* For LZX compression, the chunk size corresponds to the LZX
+ * window size, which according the LZX specification can be any
+ * power of 2 between 2^15 and 2^21, inclusively. All these are
+ * supported by wimlib; however, unfortunately only 2^15 is
+ * supported by WIMGAPI[1] so this value is used by default.
+ *
+ * [1] WIMGAPI (Windows 7) attempts to decompress LZX chunk
+ * sizes > 2^15 but seems to have bug(s) that cause it to fail
+ * or crash. (I tried several tweaks to the LZX data but none
+ * resulted in successful decompression.) WIMGAPI (Windows 8)
+ * appears to refuse to open WIMs with chunk size > 2^15
+ * entirely. */
+ return order >= 15 && order <= 21;
+
+ case WIMLIB_COMPRESSION_TYPE_XPRESS:
+ /* WIMGAPI (Windows 7, Windows 8) doesn't seem to support XPRESS
+ * chunk size below 32768 bytes, but larger power-of-two sizes,
+ * up ta 67108864 bytes, appear to work. (Note, however, that
+ * the offsets of XPRESS matches are still limited to 65535
+ * bytes even when a much larger chunk size is used!) */
+ return order >= 15 && order <= 26;
+
+ case WIMLIB_COMPRESSION_TYPE_LZMS:
+ return order >= 15 && order <= 26;
+ }
+ return false;
+}
+
+/* Return the default chunk size to use for the specified compression type.
+ *
+ * See notes above in wim_chunk_size_valid(). */
+static u32
+wim_default_chunk_size(int ctype)
+{
+ switch (ctype) {
+ case WIMLIB_COMPRESSION_TYPE_LZMS:
+ return 1U << 17; /* 131072 */
+ default:
+ return 1U << 15; /* 32768 */
+ }
+}
+