Hi Junio,
On Fri, 17 Feb 2017, Junio C Hamano wrote:
> Johannes Schindelin <johannes.schinde...@gmx.de> writes:
>
> > diff --git a/hashmap.c b/hashmap.c
> > index b10b642229c..061b7d61da6 100644
> > --- a/hashmap.c
> > +++ b/hashmap.c
> > @@ -50,6 +50,20 @@ unsigned int memihash(const void *buf, size_t len)
> > return hash;
> > }
> >
> > +/* Incoporate another chunk of data into a memihash computation. */
> > +unsigned int memihash_continue(unsigned int hash,
> > + const void *buf, size_t len)
> > +{
> > + const unsigned char *p = buf;
> > + while (len--) {
> > + unsigned int c = *p++;
> > + if (c >= 'a' && c <= 'z')
> > + c -= 'a' - 'A';
> > + hash = (hash * FNV32_PRIME) ^ c;
> > + }
> > + return hash;
> > +}
>
> This makes me wonder if we want to reduce the duplication (primarily
> to avoid risking the loop body to go out of sync) by doing:
>
> unsigned int memihash(const void *buf, size_t len)
> {
> return memihash_continue(buf, len, FNV32_BASE);
> }
>
> If an extra call level really matters, its "inline" equivalent in
> the header would probably be good.
Well, the hashing is supposed to be as fast as possible, so I would like
to avoid that extra call level. However, the end result is not so pretty
because FNV32_BASE needs to be made public (OTOH it removes more lines
than it adds):
-- snipsnap --
diff --git a/hashmap.c b/hashmap.c
index 061b7d61da6..470a0832688 100644
--- a/hashmap.c
+++ b/hashmap.c
@@ -4,7 +4,6 @@
#include "cache.h"
#include "hashmap.h"
-#define FNV32_BASE ((unsigned int) 0x811c9dc5)
#define FNV32_PRIME ((unsigned int) 0x01000193)
unsigned int strhash(const char *str)
@@ -37,19 +36,6 @@ unsigned int memhash(const void *buf, size_t len)
return hash;
}
-unsigned int memihash(const void *buf, size_t len)
-{
- unsigned int hash = FNV32_BASE;
- unsigned char *ucbuf = (unsigned char *) buf;
- while (len--) {
- unsigned int c = *ucbuf++;
- if (c >= 'a' && c <= 'z')
- c -= 'a' - 'A';
- hash = (hash * FNV32_PRIME) ^ c;
- }
- return hash;
-}
-
/* Incoporate another chunk of data into a memihash computation. */
unsigned int memihash_continue(unsigned int hash,
const void *buf, size_t len)
diff --git a/hashmap.h b/hashmap.h
index 78e14dfde71..a1a8fd7dc54 100644
--- a/hashmap.h
+++ b/hashmap.h
@@ -8,12 +8,17 @@
/* FNV-1 functions */
+#define FNV32_BASE ((unsigned int) 0x811c9dc5)
+
extern unsigned int strhash(const char *buf);
extern unsigned int strihash(const char *buf);
extern unsigned int memhash(const void *buf, size_t len);
-extern unsigned int memihash(const void *buf, size_t len);
extern unsigned int memihash_continue(unsigned int hash_seed,
const void *buf, size_t len);
+static inline unsigned int memihash(const void *buf, size_t len)
+{
+ return memihash_continue(FNV32_BASE, buf, len);
+}
static inline unsigned int sha1hash(const unsigned char *sha1)
{
