Fix mishandling of symbols that look like numbers

* src/bignum.c (make_neg_biguint): New function.
* src/lread.c (read1): Do not mishandle an unquoted symbol
with name equal to something like "1\0x", i.e., a string
of numeric form followed by a NUL byte.
Formerly these symbols were misread as numbers.
(string_to_number): Change last argument from an integer flag
to a pointer to the length.  This lets the caller figure out
how much of the prefix was used.  All callers changed.
Add a fast path if the integer (sans sign) fits in uintmax_t.
Update comments and simplify now that bignums are present.
* src/print.c (print_object): Fix quoting of symbols that look
like numbers, by relying on string_to_number for the tricky
cases rather than trying to redo its logic, incorrectly.  For
example, (read (prin1-to-string '\1e+NaN)) formerly returned
"1e+NaN", which was wrong: a backslash is needed in the output
to prevent it from being read as a NaN.  Escape NO_BREAK_SPACE
too, since lread.c treats it like SPACE.
* test/src/print-tests.el (print-read-roundtrip):
Add tests illustrating the abovementioned bugs.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 2c20b483cad..5ecc48b025c 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -2506,7 +2506,7 @@ INTEGERP (Lisp_Object x)
   return FIXNUMP (x) || BIGNUMP (x);
 }
 
-/* Return a Lisp integer with value taken from n.  */
+/* Return a Lisp integer with value taken from N.  */
 INLINE Lisp_Object
 make_int (intmax_t n)
 {
@@ -3329,6 +3329,7 @@ extern ptrdiff_t bignum_bufsize (Lisp_Object, int);
 extern ptrdiff_t bignum_to_c_string (char *, ptrdiff_t, Lisp_Object, int);
 extern Lisp_Object bignum_to_string (Lisp_Object, int);
 extern Lisp_Object make_bignum_str (char const *, int);
+extern Lisp_Object make_neg_biguint (uintmax_t);
 extern Lisp_Object double_to_integer (double);
 
 /* Converthe integer NUM to *N.  Return true if successful, false
@@ -3839,7 +3840,7 @@ LOADHIST_ATTACH (Lisp_Object x)
 extern int openp (Lisp_Object, Lisp_Object, Lisp_Object,
                   Lisp_Object *, Lisp_Object, bool);
 enum { S2N_IGNORE_TRAILING = 1 };
-extern Lisp_Object string_to_number (char const *, int, int);
+extern Lisp_Object string_to_number (char const *, int, ptrdiff_t *);
 extern void map_obarray (Lisp_Object, void (*) (Lisp_Object, Lisp_Object),
                          Lisp_Object);
 extern void dir_warning (const char *, Lisp_Object);