Patchwork [v2,34/45] host-utils: add ffsl

login
register
mail settings
Submitter Paolo Bonzini
Date Sept. 26, 2012, 3:56 p.m.
Message ID <1348675011-8794-35-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/187124/
State New
Headers show

Comments

Paolo Bonzini - Sept. 26, 2012, 3:56 p.m.
We can provide fast versions based on the other functions defined
by host-utils.h.  Some care is required on glibc, which provides
ffsl already.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 host-utils.h | 26 ++++++++++++++++++++++++++
 1 file modificato, 26 inserzioni(+)
Eric Blake - Sept. 27, 2012, 1:14 a.m.
On 09/26/2012 09:56 AM, Paolo Bonzini wrote:
> We can provide fast versions based on the other functions defined
> by host-utils.h.  Some care is required on glibc, which provides
> ffsl already.
> 

Why glibc chose <string.h> for ffsl even though it uses <strings.h> for
ffs (per POSIX) is beyond me.  At any rate, this report spurred me to
finally file an enhancement request against POSIX:

http://www.austingroupbugs.net/view.php?id=617

Someday in the future, we might just get ffsl standardized. :)

Patch

diff --git a/host-utils.h b/host-utils.h
index 821db93..2724be0 100644
--- a/host-utils.h
+++ b/host-utils.h
@@ -24,6 +24,7 @@ 
  */
 
 #include "compiler.h"   /* QEMU_GNUC_PREREQ */
+#include <string.h>     /* ffsl */
 
 #if defined(__x86_64__)
 #define __HAVE_FAST_MULU64__
@@ -234,3 +235,28 @@  static inline int ctpop64(uint64_t val)
     return val;
 #endif
 }
+
+/* glibc does not provide an inline version of ffsl, so always define
+ * ours.  We need to give it a different name, however.
+ */
+#ifdef __GLIBC__
+#define ffsl qemu_ffsl
+#endif
+static inline int ffsl(long val)
+{
+    if (!val) {
+        return 0;
+    }
+
+#if QEMU_GNUC_PREREQ(3, 4)
+    return __builtin_ctzl(val) + 1;
+#else
+    if (sizeof(long) == 4) {
+        return ctz32(val) + 1;
+    } else if (sizeof(long) == 8) {
+        return ctz64(val) + 1;
+    } else {
+        abort();
+    }
+#endif
+}