[ovs-dev] [PATCH] hash: Convert macros to inline functions.

[Ben Pfaff]

I always assumed that macros would generate better code.  I was wrong.  The
generated code was identical with inline functions, with GCC version 4.4.5.

Signed-off-by: Ben Pfaff <blp at nicira.com>
---
 lib/hash.c |   12 ++++++------
 lib/hash.h |   50 ++++++++++++++++++++++++++++----------------------
 2 files changed, 34 insertions(+), 28 deletions(-)

diff --git a/lib/hash.c b/lib/hash.c
index 61e17b2..b3d9156 100644
--- a/lib/hash.c
+++ b/lib/hash.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2012 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,7 +30,7 @@ hash_words(const uint32_t *p, size_t n, uint32_t basis)
         a += p[0];
         b += p[1];
         c += p[2];
-        HASH_MIX(a, b, c);
+        hash_mix(&a, &b, &c);
         n -= 3;
         p += 3;
     }
@@ -44,7 +44,7 @@ hash_words(const uint32_t *p, size_t n, uint32_t basis)
         /* fall through */
     case 1:
         a += p[0];
-        HASH_FINAL(a, b, c);
+        hash_final(&a, &b, &c);
         /* fall through */
     case 0:
         break;
@@ -59,7 +59,7 @@ hash_3words(uint32_t a, uint32_t b, uint32_t c)
     a += 0xdeadbeef;
     b += 0xdeadbeef;
     c += 0xdeadbeef;
-    HASH_FINAL(a, b, c);
+    hash_final(&a, &b, &c);
     return c;
 }
 
@@ -85,7 +85,7 @@ hash_bytes(const void *p_, size_t n, uint32_t basis)
         a += tmp[0];
         b += tmp[1];
         c += tmp[2];
-        HASH_MIX(a, b, c);
+        hash_mix(&a, &b, &c);
         n -= sizeof tmp;
         p += sizeof tmp;
     }
@@ -96,7 +96,7 @@ hash_bytes(const void *p_, size_t n, uint32_t basis)
         a += tmp[0];
         b += tmp[1];
         c += tmp[2];
-        HASH_FINAL(a, b, c);
+        hash_final(&a, &b, &c);
     }
 
     return c;
diff --git a/lib/hash.h b/lib/hash.h
index 026eeda..05799b2 100644
--- a/lib/hash.h
+++ b/lib/hash.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010 Nicira Networks.
+ * Copyright (c) 2008, 2009, 2010, 2012 Nicira Networks.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,28 +29,34 @@ extern "C" {
 /* This is the public domain lookup3 hash by Bob Jenkins from
  * http://burtleburtle.net/bob/c/lookup3.c, modified for style. */
 
-#define HASH_ROT(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
+static inline uint32_t
+hash_rot(uint32_t x, int k)
+{
+    return (x << k) | (x >> (32 - k));
+}
 
-#define HASH_MIX(a, b, c)                       \
-    do {                                        \
-      a -= c; a ^= HASH_ROT(c,  4); c += b;     \
-      b -= a; b ^= HASH_ROT(a,  6); a += c;     \
-      c -= b; c ^= HASH_ROT(b,  8); b += a;     \
-      a -= c; a ^= HASH_ROT(c, 16); c += b;     \
-      b -= a; b ^= HASH_ROT(a, 19); a += c;     \
-      c -= b; c ^= HASH_ROT(b,  4); b += a;     \
-    } while (0)
+static inline void
+hash_mix(uint32_t *a, uint32_t *b, uint32_t *c)
+{
+      *a -= *c; *a ^= hash_rot(*c,  4); *c += *b;
+      *b -= *a; *b ^= hash_rot(*a,  6); *a += *c;
+      *c -= *b; *c ^= hash_rot(*b,  8); *b += *a;
+      *a -= *c; *a ^= hash_rot(*c, 16); *c += *b;
+      *b -= *a; *b ^= hash_rot(*a, 19); *a += *c;
+      *c -= *b; *c ^= hash_rot(*b,  4); *b += *a;
+}
 
-#define HASH_FINAL(a, b, c)                     \
-    do {                                        \
-      c ^= b; c -= HASH_ROT(b, 14);             \
-      a ^= c; a -= HASH_ROT(c, 11);             \
-      b ^= a; b -= HASH_ROT(a, 25);             \
-      c ^= b; c -= HASH_ROT(b, 16);             \
-      a ^= c; a -= HASH_ROT(c,  4);             \
-      b ^= a; b -= HASH_ROT(a, 14);             \
-      c ^= b; c -= HASH_ROT(b, 24);             \
-    } while (0)
+static inline void
+hash_final(uint32_t *a, uint32_t *b, uint32_t *c)
+{
+      *c ^= *b; *c -= hash_rot(*b, 14);
+      *a ^= *c; *a -= hash_rot(*c, 11);
+      *b ^= *a; *b -= hash_rot(*a, 25);
+      *c ^= *b; *c -= hash_rot(*b, 16);
+      *a ^= *c; *a -= hash_rot(*c,  4);
+      *b ^= *a; *b -= hash_rot(*a, 14);
+      *c ^= *b; *c -= hash_rot(*b, 24);
+}
 
 uint32_t hash_words(const uint32_t *, size_t n_word, uint32_t basis);
 uint32_t hash_2words(uint32_t, uint32_t);
@@ -87,7 +93,7 @@ static inline uint32_t hash_boolean(bool x, uint32_t basis)
 {
     const uint32_t P0 = 0xc2b73583;   /* This is hash_int(1, 0). */
     const uint32_t P1 = 0xe90f1258;   /* This is hash_int(2, 0). */
-    return (x ? P0 : P1) ^ HASH_ROT(basis, 1);
+    return (x ? P0 : P1) ^ hash_rot(basis, 1);
 }
 
 static inline uint32_t hash_double(double x, uint32_t basis)
-- 
1.7.2.5