The branch main has been updated by dougm:
URL:
https://cgit.FreeBSD.org/src/commit/?id=9ff1462976fce4f4389be9a3357eadd22d04d308
commit 9ff1462976fce4f4389be9a3357eadd22d04d308
Author: Doug Moore <do...@freebsd.org>
AuthorDate: 2024-06-04 18:00:25 +0000
Commit: Doug Moore <do...@freebsd.org>
CommitDate: 2024-06-04 18:00:25 +0000
x86: simplify ceil(log2(x)) function
A function called mask_width in one place and log2 in the other
calculates its value in a more complex way than necessary. A simpler
implementation offered here saves a few bytes in the functions that
call it.
Reviewed by: alc, avg
Differential Revision: https://reviews.freebsd.org/D45483
---
sys/amd64/vmm/x86.c | 5 ++---
sys/x86/x86/mp_x86.c | 6 ++----
2 files changed, 4 insertions(+), 7 deletions(-)
diff --git a/sys/amd64/vmm/x86.c b/sys/amd64/vmm/x86.c
index 3cf689217590..aa8f87c98fe8 100644
--- a/sys/amd64/vmm/x86.c
+++ b/sys/amd64/vmm/x86.c
@@ -61,14 +61,13 @@ SYSCTL_INT(_hw_vmm_topology, OID_AUTO, cpuid_leaf_b,
CTLFLAG_RDTUN,
&cpuid_leaf_b, 0, NULL);
/*
- * Round up to the next power of two, if necessary, and then take log2.
- * Returns -1 if argument is zero.
+ * Compute ceil(log2(x)). Returns -1 if x is zero.
*/
static __inline int
log2(u_int x)
{
- return (fls(x << (1 - powerof2(x))) - 1);
+ return (x == 0 ? -1 : fls(x - 1));
}
int
diff --git a/sys/x86/x86/mp_x86.c b/sys/x86/x86/mp_x86.c
index 1027c2c8972b..3c08f7fa987d 100644
--- a/sys/x86/x86/mp_x86.c
+++ b/sys/x86/x86/mp_x86.c
@@ -183,15 +183,13 @@ mem_range_AP_init(void)
}
/*
- * Round up to the next power of two, if necessary, and then
- * take log2.
- * Returns -1 if argument is zero.
+ * Compute ceil(log2(x)). Returns -1 if x is zero.
*/
static __inline int
mask_width(u_int x)
{
- return (fls(x << (1 - powerof2(x))) - 1);
+ return (x == 0 ? -1 : fls(x - 1));
}
/*
