Re: [PATCH v2] builtin-fast-export: Add importing and exporting of revision marks

Pieter de Bie [off-list ref] writes:

+static void export_marks(char *file)
+{
+	unsigned int i;
+	uint32_t mark;
+	struct object_decoration *deco = idnums.hash;
+	FILE *f;
+
+	f = fopen(file, "w");
+	if (!f)
+		error("Unable to open marks file %s for writing", file);
+
+	for (i = 0; i < idnums.size; ++i) {
+		deco++;
...
+			mark = (uint32_t *)deco->decoration - (uint32_t *)NULL;
+			fprintf(f, ":%u %s\n", mark,
+				sha1_to_hex(deco->base->sha1));
...
+}
+
+static void import_marks(char * input_file)
...
+		add_decoration(&idnums, object, ((uint32_t *)NULL) + mark);

I am confused.

The type of object_decoration.decorattion is a (void*).  Why isn't it
sufficient to do it in a naïve and straightforward way?

	mark = (uint32_t)(deco->decoration);
        add_decoration(&idnums, object, (void*) mark);

Is this twisted pointer arithmetic done in order to avoid cast between int
and pointer of different size in the code?  Even if that is the case,
doesn't "(uint32_t *)deco->decoration - (uint32_t *)NULL" mean the value
range for deco->decoration is one-fourth of U32?  What are you gaining
from using "uint32_t *" instead of some other pointer types, say "char *"?