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Improve documentation of hash-code functions

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* src/fns.c (Fsxhash_eq, Fsxhash_eql, Fsxhash_equal):
* doc/lispref/hash.texi (Defining Hash): Warn against assuming
that sxhash returns consistent results.
This commit is contained in:
Eli Zaretskii 2019-06-15 11:16:49 +03:00
parent f6a1647a8b
commit 333170348b
2 changed files with 14 additions and 3 deletions
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5
doc/lispref/hash.texi
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@ -333,6 +333,11 @@ and equal-looking objects are considered the same key.
(make-hash-table :test 'contents-hash)
@end example
Lisp programs should @emph{not} rely on hash codes being preserved
between Emacs sessions, as the implementation of the hash functions
uses some details of the object storage that can change between
sessions and between different architectures.
@node Other Hash
@section Other Hash Table Functions

12
src/fns.c
View file

@ -4695,7 +4695,9 @@ sxhash (Lisp_Object obj, int depth)
DEFUN ("sxhash-eq", Fsxhash_eq, Ssxhash_eq, 1, 1, 0,
doc: /* Return an integer hash code for OBJ suitable for `eq'.
If (eq A B), then (= (sxhash-eq A) (sxhash-eq B)). */)
If (eq A B), then (= (sxhash-eq A) (sxhash-eq B)).
Hash codes are not guaranteed to be preserved across Emacs sessions. */)
(Lisp_Object obj)
{
return make_fixnum (hashfn_eq (NULL, obj));
@ -4703,7 +4705,9 @@ If (eq A B), then (= (sxhash-eq A) (sxhash-eq B)). */)
DEFUN ("sxhash-eql", Fsxhash_eql, Ssxhash_eql, 1, 1, 0,
doc: /* Return an integer hash code for OBJ suitable for `eql'.
If (eql A B), then (= (sxhash-eql A) (sxhash-eql B)). */)
If (eql A B), then (= (sxhash-eql A) (sxhash-eql B)).
Hash codes are not guaranteed to be preserved across Emacs sessions. */)
(Lisp_Object obj)
{
return make_fixnum (hashfn_eql (NULL, obj));
@ -4711,7 +4715,9 @@ If (eql A B), then (= (sxhash-eql A) (sxhash-eql B)). */)
DEFUN ("sxhash-equal", Fsxhash_equal, Ssxhash_equal, 1, 1, 0,
doc: /* Return an integer hash code for OBJ suitable for `equal'.
If (equal A B), then (= (sxhash-equal A) (sxhash-equal B)). */)
If (equal A B), then (= (sxhash-equal A) (sxhash-equal B)).
Hash codes are not guaranteed to be preserved across Emacs sessions. */)
(Lisp_Object obj)
{
return make_fixnum (hashfn_equal (NULL, obj));