Introduce likely/unlikely macros, use them in saa.c

Introduce the likely() and unlikely() macros, as used in Linux.
They are compiler-dependent hints that a particular boolean expression
is likely to be true or false, respectively.

Currently only implemented for gcc.

2 files changed, 14 insertions, 2 deletions

diff --git a/compiler.h b/compiler.h
index 01e1127..51f4983 100644
--- a/compiler.h
+++ b/compiler.h
@@ -110,4 +110,16 @@ char *strsep(char **, const char *);
 # define X86_MEMORY 0
 #endif
 
+/*
+ * Hints to the compiler that a particular branch of code is more or
+ * less likely to be taken.
+ */
+#if defined(__GNUC__) && __GNUC__ >= 3
+# define likely(x)	__builtin_expect(!!(x), 1)
+# define unlikely(x)	__builtin_expect(!!(x), 0)
+#else
+# define likely(x)	(!!(x))
+# define unlikely(x)	(!!(x))
+#endif
+
 #endif	/* NASM_COMPILER_H */
diff --git a/saa.c b/saa.c
index 51123da..1704b7d 100644
--- a/saa.c
+++ b/saa.c
@@ -211,7 +211,7 @@ void saa_fread(struct SAA *s, size_t posn, void *data, size_t len)
 	return;
     }
 
-    if (s->blk_len == SAA_BLKLEN) {
+    if (likely(s->blk_len == SAA_BLKLEN)) {
 	ix = posn >> SAA_BLKSHIFT;
 	s->rpos = posn & (SAA_BLKLEN-1);
     } else {
@@ -235,7 +235,7 @@ void saa_fwrite(struct SAA *s, size_t posn, const void *data, size_t len)
 	return;
     }
     
-    if (s->blk_len == SAA_BLKLEN) {
+    if (likely(s->blk_len == SAA_BLKLEN)) {
 	ix = posn >> SAA_BLKSHIFT;
 	s->wpos = posn & (SAA_BLKLEN-1);
     } else {