Use only SIZEOF_OFF_T to determine "large file support"

Author: kyz

libmspack/ChangeLog

@@ -1,3 +1,21 @@
+2020-04-13  Stuart Caie <[email protected]>
+
+	* system.h: clear up libmspack's large file support.
+
+	To support large files, do this:
+
+	1. add any defines that your compiler needs to enable large file
+	support. It may be supported by default.
+	2. Define HAVE_FSEEKO if fseeko() and ftello() are available.
+	3. Define SIZEOF_OFF_T to the value of sizeof(off_t); it must be a
+	literal value because sizeof() can't be used in preprocessor tests.
+
+	libmspack uses the off_t datatype for all file offsets. If off_t is
+	less than 64 bits, libmspack will return an error when processing
+	CHM files with offsets beyond 2GB, and won't search for CAB headers
+	beyond 2GB into a file.  In both cases, it prints a warning message
+	that the library doesn't support large files.
+
 2020-04-13  Stuart Caie <[email protected]>
 
 	* macros.h: new header for the D(), LD/LU and EndGet???() macros.

libmspack/mspack/cabd.c

@@ -651,10 +651,10 @@ static int cabd_find(struct mscab_decompressor_p *self, unsigned char *buf,
   unsigned int cablen_u32 = 0, foffset_u32 = 0;
   int false_cabs = 0;
 
-#if !LARGEFILE_SUPPORT
+#if SIZEOF_OFF_T < 8
   /* detect 32-bit off_t overflow */
   if (flen < 0) {
-    sys->message(fh, largefile_msg);
+    sys->message(fh, "library not compiled to support large files.");
     return MSPACK_ERR_OK;
   }
 #endif
@@ -753,10 +753,10 @@ static int cabd_find(struct mscab_decompressor_p *self, unsigned char *buf,
             /* cause the search to restart after this cab's data. */
             offset = caboff + (off_t) cablen_u32;
 
-#if !LARGEFILE_SUPPORT
+#if SIZEOF_OFF_T < 8
             /* detect 32-bit off_t overflow */
             if (offset < caboff) {
-              sys->message(fh, largefile_msg);
+              sys->message(fh, "library not compiled to support large files.");
               return MSPACK_ERR_OK;
             }
 #endif        

libmspack/mspack/chmd.c

@@ -1364,12 +1364,12 @@ static int chmd_error(struct mschm_decompressor *base) {
 static int read_off64(off_t *var, unsigned char *mem,
                       struct mspack_system *sys, struct mspack_file *fh)
 {
-#if LARGEFILE_SUPPORT
+#if SIZEOF_OFF_T >= 8
     *var = EndGetI64(mem);
 #else
     *var = EndGetI32(mem);
     if ((*var & 0x80000000) || EndGetI32(mem+4)) {
-        sys->message(fh, (char *)largefile_msg);
+        sys->message(fh, "library not compiled to support large files.");
         return 1;
     }
 #endif

libmspack/mspack/system.c

@@ -13,11 +13,6 @@
 
 #include <system.h>
 
-#if !LARGEFILE_SUPPORT
-const char *largefile_msg = "library not compiled to support large files.";
-#endif
-
-
 int mspack_version(int entity) {
   switch (entity) {
    /* CHM decoder version 1 -> 2 changes:

libmspack/mspack/system.h

@@ -49,23 +49,6 @@ static inline size_t strlen(const char *s) {
 # undef read
 #endif
 
-/* CAB supports searching through files over 4GB in size, and the CHM file
- * format actively uses 64-bit offsets. These can only be fully supported
- * if the system the code runs on supports large files. If not, the library
- * will work as normal using only 32-bit arithmetic, but if an offset
- * greater than 2GB is detected, an error message indicating the library
- * can't support the file should be printed.
- */
-#include <limits.h>
-#if ((defined(_FILE_OFFSET_BITS) && _FILE_OFFSET_BITS >= 64) || \
-     (defined(FILESIZEBITS)      && FILESIZEBITS      >= 64) || \
-     defined(_LARGEFILE_SOURCE) || defined(_LARGEFILE64_SOURCE) || \
-     SIZEOF_OFF_T >= 8)
-# define LARGEFILE_SUPPORT 1
-#else
-extern const char *largefile_msg;
-#endif
-
 extern struct mspack_system *mspack_default_system;
 
 /* returns the length of a file opened for reading */