core/utils.h: add OSMO_LIKELY / OSMO_UNLIKELY macros
These macros are built on top of the __builtin_expect() function [1],
which provides the compiler with branch prediction information.
Similar macros exist in the Linux kernel: likely() / unlikely().
[1] https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
Change-Id: I0b029654ba050f079eed4a0574a3fa8019677067
diff --git a/include/osmocom/core/utils.h b/include/osmocom/core/utils.h
index eda0e39..7625da1 100644
--- a/include/osmocom/core/utils.h
+++ b/include/osmocom/core/utils.h
@@ -38,6 +38,15 @@
/*! Copy a C-string into a sized buffer using sizeof to detect buffer's size */
#define OSMO_STRLCPY_ARRAY(array, src) osmo_strlcpy(array, src, sizeof(array))
+/*! Branch prediction optimizations */
+#if defined(__GNUC__)
+#define OSMO_LIKELY(exp) __builtin_expect(!!(exp), 1)
+#define OSMO_UNLIKELY(exp) __builtin_expect(!!(exp), 0)
+#else
+#define OSMO_LIKELY(exp) exp
+#define OSMO_UNLIKELY(exp) exp
+#endif
+
/*! A mapping between human-readable string and numeric value */
struct value_string {
uint32_t value; /*!< numeric value */