From 30cbcafc05658c25cd0b166c47d318786fea14ba Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Sun, 25 Feb 2018 21:04:45 -0500 Subject: [PATCH] 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. --- qemu/include/qemu/osdep.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/qemu/include/qemu/osdep.h b/qemu/include/qemu/osdep.h index c3c61fe8..530d1f2e 100644 --- a/qemu/include/qemu/osdep.h +++ b/qemu/include/qemu/osdep.h @@ -141,7 +141,8 @@ /* 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 */ @@ -172,6 +173,9 @@ #define QEMU_PTR_IS_ALIGNED(p, n) QEMU_IS_ALIGNED((uintptr_t)(p), (n)) #endif +/* 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