Support special value "max" where xz and xzdec accept an integer.

Don't round the memory usage limit in xzdec --help to avoid
an integer overflow and to not give wrong impression that
the limit is high enough when it may not actually be.

src/xz/util.c

@@ -45,6 +45,10 @@ str_to_uint64(const char *name, const char *value, uint64_t min, uint64_t max)
 	while (*value == ' ' || *value == '\t')
 		++value;
 
+	// Accept special value "max". Supporting "min" doesn't seem useful.
+	if (strcmp(value, "max") == 0)
+		return max;
+
 	if (*value < '0' || *value > '9')
 		message_fatal(_("%s: Value is not a non-negative "
 				"decimal integer"), value);

src/xzdec/xzdec.c

@@ -86,7 +86,7 @@ help(void)
 		" MiB of memory at maximum.\n"
 "\n"
 "Report bugs to <" PACKAGE_BUGREPORT "> (in English or Finnish).\n",
-		argv0, (memlimit + 512 * 1024) / (1024 * 1024));
+		argv0, memlimit / (1024 * 1024));
 	my_exit();
 }
 
@@ -128,6 +128,10 @@ str_to_uint64(const char *value)
 {
 	uint64_t result = 0;
 
+	// Accept special value "max".
+	if (strcmp(value, "max") == 0)
+		return UINT64_MAX;
+
 	if (*value < '0' || *value > '9') {
 		fprintf(stderr, "%s: %s: Not a number\n", argv0, value);
 		exit(EXIT_FAILURE);