The is_binary flag needs only three values: -1, 0, and 1.
However, we use a whole 32-bit int for it on most systems
(both 32- and 64- bit).

Instead, we can mark it to use only 2 bits. On 32-bit
systems, this lets it end up as part of the bitfield above
(saving 4 bytes). On 64-bit systems, we don't see any change
(because the savings end up as padding), but it does leave
room for another "free" 32-bit value to be added later.

Signed-off-by: Jeff King <>
I don't typically use bit-sized integers like this for anything but
unsigned integers to be used as flags. My understanding is that using
signed integers is explicitly permitted by the standard. I don't know if
we're guaranteed a 2's-complement representation, but I can't imagine an
implementation providing any range besides -2..1, which is what we need.

 diffcore.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/diffcore.h b/diffcore.h
index d911bf0..79de8cf 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -46,7 +46,7 @@ struct diff_filespec {
        unsigned is_stdin : 1;
        unsigned has_more_entries : 1; /* only appear in combined diff */
        /* data should be considered "binary"; -1 means "don't know yet" */
-       int is_binary;
+       int is_binary : 2;
        struct userdiff_driver *driver;
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