MINOR: tools: implement my_flsl()
We already have my_ffsl() to find the lowest bit set in a word, and
this patch implements the search for the highest bit set in a word.
On x86 it uses the bsr instruction and on other architectures it
uses an efficient implementation.
diff --git a/include/common/standard.h b/include/common/standard.h
index 87d5f88..7536a64 100644
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -808,7 +808,7 @@
}
/* Simple ffs implementation. It returns the position of the lowest bit set to
- * one. It is illegal to call it with a==0 (undefined result).
+ * one, starting at 1. It is illegal to call it with a==0 (undefined result).
*/
static inline unsigned int my_ffsl(unsigned long a)
{
@@ -851,6 +851,50 @@
return cnt;
}
+/* Simple fls implementation. It returns the position of the highest bit set to
+ * one, starting at 1. It is illegal to call it with a==0 (undefined result).
+ */
+static inline unsigned int my_flsl(unsigned long a)
+{
+ unsigned long cnt;
+
+#if defined(__x86_64__)
+ __asm__("bsr %1,%0\n" : "=r" (cnt) : "rm" (a));
+ cnt++;
+#else
+
+ cnt = 1;
+#if LONG_MAX > 0x7FFFFFFFUL /* 64bits */
+ if (a & 0xFFFFFFFF00000000UL) {
+ a >>= 32;
+ cnt += 32;
+ }
+#endif
+ if (a & 0XFFFF0000U) {
+ a >>= 16;
+ cnt += 16;
+ }
+ if (a & 0XFF00) {
+ a >>= 8;
+ cnt += 8;
+ }
+ if (a & 0xf0) {
+ a >>= 4;
+ cnt += 4;
+ }
+ if (a & 0xc) {
+ a >>= 2;
+ cnt += 2;
+ }
+ if (a & 0x2) {
+ a >>= 1;
+ cnt += 1;
+ }
+#endif /* x86_64 */
+
+ return cnt;
+}
+
/* Build a word with the <bits> lower bits set (reverse of my_popcountl) */
static inline unsigned long nbits(int bits)
{