Calc; Fix c type hex parse on `quick-calc'

[OGAWA Hirofumi]

This bug is reproducible with following commands.

$ emacs -Q
M-: (setq calc-language 'c)
M-x quick-calc

Quick calc: 1024 + 0x20
Result: 32 =>  32  (0x20, 040, 2#100000, " ")

Like above, the result is wrong (expected result is following).
Result: 1024 + 32 =>  1056  (0x420, 02040, 2#10000100000)

The bug is in `math-read-token'.

     (or (and (memq calc-language calc-lang-c-type-hex)
              (string-match "0[xX][0-9a-fA-F]+" math-exp-str math-exp-pos))

We want to get "1024" as token at first, but the above part matches at
"0x20" part of expr, and skips "1024 + ".

In this context, we want to check if current token is matching to
c-type hex or not. So we should check regex is matched at
math-exp-pos. This patch fixes this bug.

Emacs  : GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.24)
 of 2017-11-10
Package: Calc
---

 lisp/calc/calc-aent.el |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff -puN lisp/calc/calc-aent.el~calc-c-lang-fix lisp/calc/calc-aent.el
--- emacs/lisp/calc/calc-aent.el~calc-c-lang-fix        2017-11-10 
03:10:09.780135078 +0900
+++ emacs-hirofumi/lisp/calc/calc-aent.el       2017-11-10 03:10:42.294060877 
+0900
@@ -728,7 +728,8 @@ in Calc algebraic input.")
                                                 math-exp-str (1- math-exp-pos))
                                   (1- math-exp-pos))))))
             (or (and (memq calc-language calc-lang-c-type-hex)
-                     (string-match "0[xX][0-9a-fA-F]+" math-exp-str 
math-exp-pos))
+                     (eq (string-match "0[xX][0-9a-fA-F]+" math-exp-str 
math-exp-pos)
+                          math-exp-pos))
                 (string-match "_?\\([0-9]+.?0*@ *\\)?\\([0-9]+.?0*' 
*\\)?\\(0*\\([2-9]\\|1[0-4]\\)\\(#[#]?\\|\\^\\^\\)[0-9a-dA-D.]+[eE][-+_]?[0-9]+\\|0*\\([2-9]\\|[0-2][0-9]\\|3[0-6]\\)\\(#[#]?\\|\\^\\^\\)[0-9a-zA-Zα-ωΑ-Ω:.]+\\|[0-9]+:[0-9:]+\\|[0-9.]+\\([eE][-+_]?[0-9]+\\)?\"?\\)?"
                                math-exp-str math-exp-pos))
             (setq math-exp-token 'number
_
-- 
OGAWA Hirofumi <address@hidden>