Document that ‘random’ is limited to fixnums

Problem reported by Pip Cet (Bug#32463#20).
* doc/lispref/numbers.texi (Random Numbers):
* src/fns.c (Frandom): Adjust doc.

doc/lispref/numbers.texi

@@ -1236,11 +1236,10 @@ other strings to choose various seed values.
 This function returns a pseudo-random integer.  Repeated calls return a
 series of pseudo-random integers.
 
-If @var{limit} is a positive integer, the value is chosen to be
+If @var{limit} is a positive fixnum, the value is chosen to be
 nonnegative and less than @var{limit}.  Otherwise, the value might be
-any integer representable in Lisp, i.e., an integer between
-@code{most-negative-fixnum} and @code{most-positive-fixnum}
-(@pxref{Integer Basics}).
+any fixnum, i.e., any integer from @code{most-negative-fixnum} through
+@code{most-positive-fixnum} (@pxref{Integer Basics}).
 
 If @var{limit} is @code{t}, it means to choose a new seed as if Emacs
 were restarting, typically from the system entropy.  On systems

src/fns.c

@@ -56,15 +56,12 @@ DEFUN ("identity", Fidentity, Sidentity, 1, 1, 0,
 }
 
 DEFUN ("random", Frandom, Srandom, 0, 1, 0,
-       doc: /* Return a pseudo-random number.
-All integers representable in Lisp, i.e. between `most-negative-fixnum'
-and `most-positive-fixnum', inclusive, are equally likely.
-
-With positive integer LIMIT, return random number in interval [0,LIMIT).
+       doc: /* Return a pseudo-random integer.
+By default, return a fixnum; all fixnums are equally likely.
+With positive fixnum LIMIT, return random integer in interval [0,LIMIT).
 With argument t, set the random number seed from the system's entropy
 pool if available, otherwise from less-random volatile data such as the time.
 With a string argument, set the seed based on the string's contents.
-Other values of LIMIT are ignored.
 
 See Info node `(elisp)Random Numbers' for more details.  */)
   (Lisp_Object limit)