Re: Add hash_pjw_s(), 2nd attempt [was: hash-pjw license]

[Jim Meyering]

Nikos Mavrogiannopoulos wrote:
> On Thu, Sep 27, 2012 at 12:12 PM, Nikos Mavrogiannopoulos
> <address@hidden> wrote:
>> 4. hash_pjw_s_no_tablesize()
>> We can eliminate (2), but still there are 3 variants of the same
>> function. Maybe it is better to keep only (4) and (1) for backwards
>> compatibility, and anybody who wants to do the % tablesize to do it
>> after calling the hash_pjw_s_no_tablesize() function?
>
> And having said that, here is that function.
...
> Subject: [PATCH] Added hash-pjw-s.
...

Hi Nikos,
Thanks for working on this.

> diff --git a/lib/hash-pjw-s.c b/lib/hash-pjw-s.c
...
> +/* hash-pjw-s.c -- compute a hash value from a string.

This new function does not care if the data being hashed are a string.
I.e., X need not be NUL-terminated.

...
> +
> +#define SIZE_BITS (sizeof (size_t) * CHAR_BIT)
> +
> +/* A hash function for char* strings of known size using

Please describe the function in terms of the parameters. i.e.,

/* Return a hash of the N bytes of X using the method described by
   Bruno Haible in http://www.haible.de/bruno/hashfunc.html.
   Note that while many hash functions reduce their result via modulo
   to a 0..table_size-1 range, this function does not do that.  */

> +   the method described by Bruno Haible.
> +   The hash output isn't restricted to any number.
> +   See http://www.haible.de/bruno/hashfunc.html.  */
> +
> +size_t
> +hash_pjw_s (const void *x, size_t x_size)

I'd rename s/x_size/n/

> +{
> +  const unsigned char *s=x;
> +  size_t h = 0;
> +  unsigned i;
> +
> +  for (i=0; i<x_size;i++)

spacing:

     for (i = 0; i < x_size; i++)

> +    h = s[i] + ((h << 9) | (h >> (SIZE_BITS - 9)));
> +
> +  return h;
> +}
> diff --git a/lib/hash-pjw-s.h b/lib/hash-pjw-s.h
> new file mode 100644
> index 0000000..8d685d6
> --- /dev/null
> +++ b/lib/hash-pjw-s.h
> @@ -0,0 +1,24 @@
> +/* hash-pjw.h -- declaration for a simple hash function
> +   Copyright (C) 2001, 2003, 2009-2012 Free Software Foundation, Inc.
> +
> +   This program is free software: you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +#include <stddef.h>
> +
> +/* Compute a hash code for a string starting at X and of size X_SIZE,

This is good, but I'd remove the reference to "a string", as above.

> +   and return the hash code. Note that unlike hash_pjw_s, it does not

Typo:

  s/hash_pjw_s/hash_pjw/

> +   return it modulo TABLESIZE.
> +   The result is platform dependent: it depends on the size of the 'size_t'
> +   type and on the signedness of the 'char' type.  */
> +extern size_t hash_pjw_s (const void *x, size_t x_size) _GL_ATTRIBUTE_PURE;
> diff --git a/modules/hash-pjw-s b/modules/hash-pjw-s
> new file mode 100644
> index 0000000..1748e65
> --- /dev/null
> +++ b/modules/hash-pjw-s
> @@ -0,0 +1,22 @@
> +Description:
> +Compute a hash value for a string of known size.

Another unwanted "string"

> +Files:
> +lib/hash-pjw-s.h
> +lib/hash-pjw-s.c
> +
> +Depends-on:
> +
> +configure.ac:
> +
> +Makefile.am:
> +lib_SOURCES += hash-pjw-s.h hash-pjw-s.c
> +
> +Include:
> +"hash-pjw-s.h"
> +
> +License:
> +LGPLv2+
> +
> +Maintainer:
> +Jim Meyering