Provide basic read only access to dictzip files

`dictzip::Istream` and `dictzip::IstreamBuf` are forked from `alpinocorpus::DzIstream` and `alpinocorpus::DzIstreamBuf` of rug-compling/alpinocorpus.

1 files changed, 59 insertions, 0 deletions

diff --git a/src/util/gzip.h b/src/util/gzip.h
new file mode 100644
index 0000000..53e59f6
--- /dev/null
+++ b/src/util/gzip.h
@@ -0,0 +1,59 @@
+#pragma once
+
+#include <cstddef>
+
+namespace {
+
+size_t const GZ_HEADER_SIZE = 10;
+
+// Gzip header fields
+size_t const GZ_HEADER_ID1 = 0;
+size_t const GZ_HEADER_ID2 = 1;
+size_t const GZ_HEADER_CM = 2;
+size_t const GZ_HEADER_FLG = 3;
+size_t const GZ_HEADER_MTIME = 4;
+size_t const GZ_HEADER_XFL = 8;
+size_t const GZ_HEADER_OS = 9;
+
+// Gzip file magic
+unsigned char const gzipId1 = 0x1f;
+unsigned char const gzipId2 = 0x8b;
+
+// Gzip compression method(s)
+unsigned char const GZ_CM_DEFLATE = 8;
+
+// Flags in GZ_HEADER_FLG
+unsigned char const GZ_FLG_TEXT = 1;
+unsigned char const GZ_FLG_HCRC = 1 << 1;
+unsigned char const GZ_FLG_EXTRA = 1 << 2;
+unsigned char const GZ_FLG_NAME = 1 << 3;
+unsigned char const GZ_FLG_COMMENT = 1 << 4;
+
+// GZ_HEADER_XFL values for deflate
+unsigned char const GZ_XFL_MAX = 2;
+unsigned char const GZ_XFL_FAST = 4;
+
+// GZ_HEADER_OS values
+unsigned char const GZ_OS_FAT = 0;
+unsigned char const GZ_OS_AMIGA = 1;
+unsigned char const GZ_OS_VMS = 2;
+unsigned char const GZ_OS_UNIX = 3;
+unsigned char const GZ_OS_VM_CMS = 4;
+unsigned char const GZ_OS_TOS = 5;
+unsigned char const GZ_OS_HPFS = 6;
+unsigned char const GZ_OS_MAC = 7;
+unsigned char const GZ_OS_ZSYSTEM = 8;
+unsigned char const GZ_OS_CPM = 9;
+unsigned char const GZ_OS_TOPS20 = 10;
+unsigned char const GZ_OS_NTFS = 11;
+unsigned char const GZ_OS_QDOS = 12;
+unsigned char const GZ_OS_RISCOS = 13;
+unsigned char const GZ_OS_UNKNOWN = 255;
+
+size_t const GZ_TRAILER_SIZE = 8;
+
+// Gzip trailer fields
+size_t const GZ_TRAILER_CRC32 = 0;
+size_t const GZ_TRAILER_ISIZE = 4;
+
+}