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-rw-r--r--README38
1 files changed, 37 insertions, 1 deletions
diff --git a/README b/README
index a0495d7197f8..566d604c15b9 100644
--- a/README
+++ b/README
@@ -7,7 +7,7 @@ XZ Embedded
XZ Embedded was written for use in the Linux kernel, but the code can
be easily used in other environments too, including regular userspace
- applications.
+ applications. See userspace/xzminidec.c for an example program.
This README contains information that is useful only when the copy
of XZ Embedded isn't part of the Linux kernel tree. You should also
@@ -84,6 +84,42 @@ Embedding into userspace applications
environment. Probably you should at least skim through it even if the
default file works as is.
+Integrity check support
+
+ XZ Embedded always supports the integrity check types None and
+ CRC32. Support for CRC64 is optional. SHA-256 is currently not
+ supported in XZ Embedded although the .xz format does support it.
+ The xz tool from XZ Utils uses CRC64 by default, but CRC32 is usually
+ enough in embedded systems to keep the code size smaller.
+
+ If you want support for CRC64, you need to copy linux/lib/xz/xz_crc64.c
+ into your application, and #define XZ_USE_CRC64 in xz_config.h or in
+ compiler flags.
+
+ When using the internal CRC32 or CRC64, their lookup tables need to be
+ initialized with xz_crc32_init() and xz_crc64_init(), respectively.
+ See xz.h for details.
+
+ To use external CRC32 or CRC64 code instead of the code from
+ xz_crc32.c or xz_crc64.c, the following #defines may be used
+ in xz_config.h or in compiler flags:
+
+ #define XZ_INTERNAL_CRC32 0
+ #define XZ_INTERNAL_CRC64 0
+
+ Then it is up to you to provide compatible xz_crc32() or xz_crc64()
+ functions.
+
+ If the .xz file being decompressed uses an integrity check type that
+ isn't supported by XZ Embedded, it is treated as an error and the
+ file cannot be decompressed. For multi-call mode, this can be modified
+ by #defining XZ_DEC_ANY_CHECK. Then xz_dec_run() will return
+ XZ_UNSUPPORTED_CHECK when unsupported check type is detected. After
+ that decompression can be continued normally except that the
+ integrity check won't be verified. In single-call mode there's
+ no way to continue decoding, so XZ_DEC_ANY_CHECK is almost useless
+ in single-call mode.
+
BCJ filter support
If you want support for one or more BCJ filters, you need to copy also