qemu/host-utils.h: Add clz and ctz functions for lower-bit integers

This is for use in the RISC-V vclz and vctz instructions (implemented in
proceeding commit).

Signed-off-by: Kiran Ostrolenk <kiran.ostrolenk@codethink.co.uk>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230428144757.57530-11-lawrence.hunter@codethink.co.uk>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h
index 3ce62bf..d3b4dce 100644
--- a/include/qemu/host-utils.h
+++ b/include/qemu/host-utils.h
@@ -108,6 +108,36 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
 #endif
 
 /**
+ * clz8 - count leading zeros in a 8-bit value.
+ * @val: The value to search
+ *
+ * Returns 8 if the value is zero.  Note that the GCC builtin is
+ * undefined if the value is zero.
+ *
+ * Note that the GCC builtin will upcast its argument to an `unsigned int`
+ * so this function subtracts off the number of prepended zeroes.
+ */
+static inline int clz8(uint8_t val)
+{
+    return val ? __builtin_clz(val) - 24 : 8;
+}
+
+/**
+ * clz16 - count leading zeros in a 16-bit value.
+ * @val: The value to search
+ *
+ * Returns 16 if the value is zero.  Note that the GCC builtin is
+ * undefined if the value is zero.
+ *
+ * Note that the GCC builtin will upcast its argument to an `unsigned int`
+ * so this function subtracts off the number of prepended zeroes.
+ */
+static inline int clz16(uint16_t val)
+{
+    return val ? __builtin_clz(val) - 16 : 16;
+}
+
+/**
  * clz32 - count leading zeros in a 32-bit value.
  * @val: The value to search
  *
@@ -154,6 +184,30 @@ static inline int clo64(uint64_t val)
 }
 
 /**
+ * ctz8 - count trailing zeros in a 8-bit value.
+ * @val: The value to search
+ *
+ * Returns 8 if the value is zero.  Note that the GCC builtin is
+ * undefined if the value is zero.
+ */
+static inline int ctz8(uint8_t val)
+{
+    return val ? __builtin_ctz(val) : 8;
+}
+
+/**
+ * ctz16 - count trailing zeros in a 16-bit value.
+ * @val: The value to search
+ *
+ * Returns 16 if the value is zero.  Note that the GCC builtin is
+ * undefined if the value is zero.
+ */
+static inline int ctz16(uint16_t val)
+{
+    return val ? __builtin_ctz(val) : 16;
+}
+
+/**
  * ctz32 - count trailing zeros in a 32-bit value.
  * @val: The value to search
  *