Remove useless test and initialisation in name to hash computation

Hello,

I think there is a minor improvment that could be performed on name to hash computation in hash.c. Before first byte modulo 4 the computed value is reinitialised, but it is already correctly initialised before loop and after having processed last byte modulo 4. So the test and initialisation seems useless.

For the kernel, this lead to following change (sorry I do not have a git version of it, so it is a simple diff):
---------------------------------------------------------------

ext4/hash.c 2017-07-24 20:42:23.000000000 +0200 renamed from ext4/hash.c.orig 2017-07-24 20:41:53.000000000 +0200 +0 -5

@@ -79,8 +79,6 @@ static void str2hashbuf_signed(const cha
        if (len > num*4)
                len = num * 4;
        for (i = 0; i < len; i++) {
-               if ((i % 4) == 0)
-                       val = pad;
                val = ((int) scp[i]) + (val << 8);
                if ((i % 4) == 3) {
                        *buf++ = val;

@@ -107,8 +105,6 @@ static void str2hashbuf_unsigned(const c
        if (len > num*4)
                len = num * 4;
        for (i = 0; i < len; i++) {
-               if ((i % 4) == 0)
-                       val = pad;
                val = ((int) ucp[i]) + (val << 8);
                if ((i % 4) == 3) {
                        *buf++ = val;
---------------------------------------------------------------

For e2fsprogs, the 2 functions are combined in one, so there is only one change:
---------------------------------------------------------------

lib/ext2fs/dirhash.c +0 -2

index c4ac94e..4ba3f35 100644
@@ -154,8 +154,6 @@ static void str2hashbuf(const char *msg, int len, __u32
 *buf, int num,
     if (len > num*4)
         len = num * 4;
     for (i=0; i < len; i++) {
-        if ((i % 4) == 0)
-            val = pad;
         if (unsigned_flag)
             c = (int) ucp[i];

else
---------------------------------------------------------------

From my limited testing the improvement seems to be around 11% for me

Regards,

Damien

Quoted 48 lines · Damien Guibouret

Hello,

I think there is a minor improvment that could be performed on name to hash computation in hash.c. Before first byte modulo 4 the computed value is reinitialised, but it is already correctly initialised before loop and after having processed last byte modulo 4. So the test and initialisation seems useless.

For the kernel, this lead to following change (sorry I do not have a git version of it, so it is a simple diff):
---------------------------------------------------------------

ext4/hash.c 2017-07-24 20:42:23.000000000 +0200 renamed from ext4/hash.c.orig 2017-07-24 20:41:53.000000000 +0200 +0 -5

@@ -79,8 +79,6 @@ static void str2hashbuf_signed(const cha
       if (len > num*4)
               len = num * 4;
       for (i = 0; i < len; i++) {
-               if ((i % 4) == 0)
-                       val = pad;
               val = ((int) scp[i]) + (val << 8);
               if ((i % 4) == 3) {
                       *buf++ = val;

@@ -107,8 +105,6 @@ static void str2hashbuf_unsigned(const c
       if (len > num*4)
               len = num * 4;
       for (i = 0; i < len; i++) {
-               if ((i % 4) == 0)
-                       val = pad;
               val = ((int) ucp[i]) + (val << 8);
               if ((i % 4) == 3) {
                       *buf++ = val;
---------------------------------------------------------------

For e2fsprogs, the 2 functions are combined in one, so there is only one change:
---------------------------------------------------------------

lib/ext2fs/dirhash.c +0 -2

index c4ac94e..4ba3f35 100644
@@ -154,8 +154,6 @@ static void str2hashbuf(const char *msg, int len, __u32
 *buf, int num,
    if (len > num*4)
        len = num * 4;
    for (i=0; i < len; i++) {
-        if ((i % 4) == 0)
-            val = pad;
        if (unsigned_flag)
            c = (int) ucp[i];

Quoted 2 lines

else
---------------------------------------------------------------

Hi Damien,

the change looks ok to me, have you done any testing to quantify the improvement, or validate the change ?

Quoted 1 line

From my limited testing the improvement seems to be around 11% for me

which would be nice to have. Also my test on 466k strings looks ok as well.

Are you willing to send out properly formated patch for kernel and e2fsprogs ?

Thanks!
-Lukas

Quoted 3 lines

Regards,

Damien