From b38f70a82b9628d80f5a9bc938a8861ee4dcf49e Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 16 Jan 2014 20:22:56 -0500 Subject: [PATCH] diff_filespec: reorder is_binary field The middle of the diff_filespec struct contains a mixture of ints, shorts, and bit-fields, followed by a pointer. On an x86-64 system with an LP64 or LLP64 data model (i.e., most of them), the integers and flags end up being padded out by 41 bits to put the pointer at an 8-byte boundary. After the pointer, we have the "int is_binary" field, which is only 32 bits. We end up wasting another 32 bits to pad the struct size up to a multiple of 64 bits. We can move the is_binary field before the pointer, which lets the compiler store it where we used to have padding. This shrinks the top padding to only 9 bits (from the bit-fields), and eliminates the bottom padding entirely, dropping the struct size from 88 to 80 bytes. On a 32-bit system, there is no benefit, but nor should there be any harm (we only need 4-byte alignment there, so we were already using only 9 bits of padding). Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- diffcore.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/diffcore.h b/diffcore.h index 22993e1eff..d911bf0a42 100644 --- a/diffcore.h +++ b/diffcore.h @@ -45,9 +45,9 @@ struct diff_filespec { #define DIRTY_SUBMODULE_MODIFIED 2 unsigned is_stdin : 1; unsigned has_more_entries : 1; /* only appear in combined diff */ - struct userdiff_driver *driver; /* data should be considered "binary"; -1 means "don't know yet" */ int is_binary; + struct userdiff_driver *driver; }; extern struct diff_filespec *alloc_filespec(const char *); -- 2.11.4.GIT