bug#46111: Reverting fns.c hash function due to OpenBSD/SPARC64 compile breaking

[Ahmed Khanzada <me@enzu.ru>]

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Not sure if the patch attached correctly. Trying again.

On Mon, Jan 25, 2021 at 10:37 PM Ahmed Khanzada <me@enzu.ru> wrote:
>
> I'm not an expert on C, OpenBSD, or SPARC64, but I did notice
> emacs-current was not compiling.
>
> During a gmake, bootstrap-emacs would get a SIGBUS and fail. Running
> gdb led me to the hash_string function where it seemed to be failing.
>
> Reverting the hash_string function to a previous version seems to have
> fixed the issue.
>
> If I had to guess, it may have something to do with SPARC64 alignment.
>
> I don't have an updated AMD64 OpenBSD box running at the moment, but if you
> would like me to test there, I could find a way.
>
> I understand that reverting this function might not be the best way
> forward, but wrote a patch just in case that reverts hash_string to an
> earlier version that compiles on OpenBSD/SPARC64.
>
> I am already signed all my GNU contributor docs.
>
> --[[text/plain; type=patch; name="0001-Reverting-hash_string-function-due-to-problem-on-Ope.patch"
> Content-Disposition: attachment; filename="0001-Reverting-hasattach filh_string-function-due-to-problem-on-Ope.patch"][base64]]
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> Cgo=

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From d938745ce56058be24078ec52d97398697db4b76 Mon Sep 17 00:00:00 2001
From: Ahmed Khanzada <me@enzu.ru>
Date: Mon, 25 Jan 2021 21:16:48 -0800
Subject: [PATCH] Reverting hash_string function due to problem on
 OpenBSD/SPARC64

---
 src/fns.c | 32 +++++++-------------------------
 1 file changed, 7 insertions(+), 25 deletions(-)

diff --git a/src/fns.c b/src/fns.c
index 7ab2e8f1a0..0127fe3f48 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -4599,34 +4599,16 @@ #define SXHASH_MAX_LEN   7
 EMACS_UINT
 hash_string (char const *ptr, ptrdiff_t len)
 {
-  EMACS_UINT const *p   = (EMACS_UINT const *) ptr;
-  EMACS_UINT const *end = (EMACS_UINT const *) (ptr + len);
-  EMACS_UINT hash = len;
-  /* At most 8 steps.  We could reuse SXHASH_MAX_LEN, of course,
-   * but dividing by 8 is cheaper.  */
-  ptrdiff_t step = 1 + ((end - p) >> 3);
-
-  /* Beware: `end` might be unaligned, so `p < end` is not always the same
-   * as `p <= end - 1`.  */
-  while (p <= end - 1)
+  char const *p = ptr;
+  char const *end = p + len;
+  unsigned char c;
+  EMACS_UINT hash = 0;
+
+  while (p != end)
     {
-      EMACS_UINT c = *p;
-      p += step;
+      c = *p++;
       hash = sxhash_combine (hash, c);
     }
-  if (p < end)
-    { /* A few last bytes remain (smaller than an EMACS_UINT).  */
-      /* FIXME: We could do this without a loop, but it'd require
-         endian-dependent code :-(  */
-      char const *p1 = (char const *)p;
-      char const *end1 = (char const *)end;
-      do
-        {
-          unsigned char c = *p1++;
-          hash = sxhash_combine (hash, c);
-        }
-      while (p1 < end1);
-    }
 
   return hash;
 }
-- 
2.28.0