From: Eric Blake Date: Thu, 21 Jul 2016 19:34:47 +0000 (-0600) Subject: osdep: Document differences in rounding macros X-Git-Tag: v2.7.0-rc2~16^2~8 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e9fd416e66539ad43bbab018f346cb164136c099;p=thirdparty%2Fqemu.git osdep: Document differences in rounding macros Make it obvious which macros are safe in which situations. Useful since QEMU_ALIGN_UP and ROUND_UP both purport to do the same thing, but differ on whether the alignment must be a power of 2. Signed-off-by: Eric Blake Message-Id: <1469129688-22848-4-git-send-email-eblake@redhat.com> Signed-off-by: Paolo Bonzini --- diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h index d7c111d1698..9e9fa615464 100644 --- a/include/qemu/osdep.h +++ b/include/qemu/osdep.h @@ -158,7 +158,8 @@ extern int daemon(int, int); /* Round number down to multiple */ #define QEMU_ALIGN_DOWN(n, m) ((n) / (m) * (m)) -/* Round number up to multiple */ +/* Round number up to multiple. Safe when m is not a power of 2 (see + * ROUND_UP for a faster version when a power of 2 is guaranteed) */ #define QEMU_ALIGN_UP(n, m) QEMU_ALIGN_DOWN((n) + (m) - 1, (m)) /* Check if n is a multiple of m */ @@ -175,6 +176,9 @@ extern int daemon(int, int); /* Check if pointer p is n-bytes aligned */ #define QEMU_PTR_IS_ALIGNED(p, n) QEMU_IS_ALIGNED((uintptr_t)(p), (n)) +/* Round number up to multiple. Requires that d be a power of 2 (see + * QEMU_ALIGN_UP for a safer but slower version on arbitrary + * numbers) */ #ifndef ROUND_UP #define ROUND_UP(n,d) (((n) + (d) - 1) & -(d)) #endif