From: Sergiy Kibrik' via OSv Development <osv-dev@googlegroups.com>
Committer: Nadav Har'El <n...@scylladb.com>
Branch: master
osv: generic bitops
Semantics of bsrq()/fls() differs on x64 and aarch64, e.g. following sample
inputs produce different results:
x64: aarch64:
bsrq(0x1) = 0 bsrq(0x1) = 63
bsrq(0xffffffffffffffff) = 63 bsrq(0xffffffffffffffff) = 0
bsrq(0x8000000000000000) = 63 bsrq(0x8000000000000000) = 0
bsrq(0x80000000) = 31 bsrq(0x80000000) = 32
bsrq(0x8008) = 15 bsrq(0x8008) = 48
bsrl(0x1) = 0 bsrl(0x1) = 63
bsrl(0xffffffff) = 31 bsrl(0xffffffff) = 32
bsrl(0x80000000) = 31 bsrl(0x80000000) = 32
bsrl(0x8008) = 15 bsrl(0x8008) = 48
fsl(0x1) = 1 fsl(0x1) = 64
fsl(0xffffffff) = 32 fsl(0xffffffff) = 33
fsl(0x80000000) = 32 fsl(0x80000000) = 33
fsl(0x8008) = 16 fsl(0x8008) = 49
Which is not quite a behaviour bitops user expects.
Use GCC built-ins to overcome this, which provide consistent behaviour
across
all platforms. Arch-specific instructions generated to avoid loops, so this
should not hurt performance.
Signed-off-by: Sergiy Kibrik <sergiy.kib...@globallogic.com>
Message-Id:
<1487597529-28580-6-git-send-email-sergiy.kib...@globallogic.com>
---
diff --git a/arch/aarch64/bitops.h b/arch/aarch64/bitops.h
--- a/arch/aarch64/bitops.h
+++ b/arch/aarch64/bitops.h
@@ -1,31 +0,0 @@
-/*
- * Copyright (C) 2014 Huawei Technologies Duesseldorf GmbH
- *
- * This work is open source software, licensed under the terms of the
- * BSD license as described in the LICENSE file in the top-level directory.
- */
-
-#ifndef ARCH_BITOPS_H_
-#define ARCH_BITOPS_H_
-static inline unsigned int
-bsrl(unsigned int mask)
-{
- unsigned int result;
- asm volatile("clz %1,%0" : "=r" (result) : "r" (mask));
- return result;
-}
-
-static inline unsigned long
-bsrq(unsigned long mask)
-{
- unsigned long result;
- asm volatile("clz %1,%0" : "=r" (result) : "r" (mask));
- return result;
-}
-
-static inline int
-fls(int mask)
-{
- return (mask == 0 ? mask : (int)bsrl((unsigned int)mask) + 1);
-}
-#endif /* ARCH_BITOPS_H */
diff --git a/bsd/porting/netport.h b/bsd/porting/netport.h
--- a/bsd/porting/netport.h
+++ b/bsd/porting/netport.h
@@ -19,7 +19,7 @@
#include <osv/debug.h>
#define __NEED_socklen_t
#include <bits/alltypes.h>
-#include "bitops.h"
+#include <osv/bitops.h>
__BEGIN_DECLS
diff --git a/core/xen_intr.cc b/core/xen_intr.cc
--- a/core/xen_intr.cc
+++ b/core/xen_intr.cc
@@ -9,7 +9,7 @@
#include <osv/xen_intr.hh>
#include <bsd/porting/bus.h>
#include <machine/intr_machdep.h>
-#include "bitops.h"
+#include <osv/bitops.h>
#include <osv/debug.hh>
#include <osv/trace.hh>
diff --git a/include/osv/bitops.h b/include/osv/bitops.h
--- a/include/osv/bitops.h
+++ b/include/osv/bitops.h
@@ -7,20 +7,16 @@
#ifndef ARCH_BITOPS_H_
#define ARCH_BITOPS_H_
-static inline unsigned int
+static inline unsigned int
bsrl(unsigned int mask)
{
- unsigned int result;
- asm volatile("bsrl %1,%0" : "=r" (result) : "rm" (mask));
- return result;
+ return sizeof(mask) * 8 - __builtin_clz(mask) - 1;
}
static inline unsigned long
bsrq(unsigned long mask)
{
- unsigned long result;
- asm volatile("bsrq %1,%0" : "=r" (result) : "rm" (mask));
- return result;
+ return sizeof(mask) * 8 - __builtin_clzl(mask) - 1;
}
static inline int
--
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