host-utils: add clrsb32/64 - count leading redundant sign bits

this patch introduces wrappers for the clrsb builtins,
which count the leading redundant sign bits.

Signed-off-by: Claudio Fontana <claudio.fontana@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>

diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h
index 0f688c1c00a792c53fe41a0e32539dac68501cb6..de85d282d024b0bed7c34fca239ef8c103d4a51e 100644 (file)
--- a/include/qemu/host-utils.h
+++ b/include/qemu/host-utils.h
@@ -227,6 +227,38 @@ static inline int cto64(uint64_t val)
     return ctz64(~val);
 }
 
+/**
+ * clrsb32 - count leading redundant sign bits in a 32-bit value.
+ * @val: The value to search
+ *
+ * Returns the number of bits following the sign bit that are equal to it.
+ * No special cases; output range is [0-31].
+ */
+static inline int clrsb32(uint32_t val)
+{
+#if QEMU_GNUC_PREREQ(4, 7)
+    return __builtin_clrsb(val);
+#else
+    return clz32(val ^ ((int32_t)val >> 1)) - 1;
+#endif
+}
+
+/**
+ * clrsb64 - count leading redundant sign bits in a 64-bit value.
+ * @val: The value to search
+ *
+ * Returns the number of bits following the sign bit that are equal to it.
+ * No special cases; output range is [0-63].
+ */
+static inline int clrsb64(uint64_t val)
+{
+#if QEMU_GNUC_PREREQ(4, 7)
+    return __builtin_clrsbll(val);
+#else
+    return clz64(val ^ ((int64_t)val >> 1)) - 1;
+#endif
+}
+
 /**
  * ctpop8 - count the population of one bits in an 8-bit value.
  * @val: The value to search