split math code out of ash and into a standalone library so we can use it in any shell (like hush!)

shell/math.h

@@ -0,0 +1,101 @@
+/* math.h - interface to shell math "library" -- this allows shells to share
+ *          the implementation of arithmetic $((...)) expansions.
+ *
+ * This aims to be a POSIX shell math library as documented here:
+ *	http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_04
+ *
+ * See math.c for internal documentation.
+ */
+
+/* The math library has just one function:
+ *
+ *	arith_t arith(const char *expr, int *perrcode, arith_eval_hooks_t *hooks);
+ *
+ *	The first argument is the math string to parse.  All normal expansions must
+ *	be done already.  i.e. no dollar symbols should be present.
+ *
+ *	The second argument is a semi-detailed error description in case something
+ *	goes wrong in the parsing steps.  Currently, those values are (for
+ *	compatibility, you should assume all negative values are errors):
+ *		 0 - no errors (yay!)
+ *		-1 - unspecified problem
+ *		-2 - divide by zero
+ *		-3 - exponent less than 0
+ *		-5 - expression recursion loop detected
+ *
+ *	The third argument is a struct pointer of hooks for your shell (see below).
+ *
+ *	The function returns the answer to the expression.  So if you called it
+ *	with the expression:
+ *		"1 + 2 + 3"
+ *	You would obviously get back 6.
+ */
+
+/* To add support to a shell, you need to implement three functions:
+ *
+ *	lookupvar() - look up and return the value of a variable
+ *
+ *		If the shell does:
+ *			foo=123
+ *		Then the code:
+ *			const char *val = lookupvar("foo");
+ *		Will result in val pointing to "123"
+ *
+ *	setvar() - set a variable to some value
+ *
+ *		If the arithmetic expansion does something like:
+ *			$(( i = 1))
+ *		Then the math code will make a call like so:
+ *			setvar("i", "1", 0);
+ *		The storage for the first two parameters are not allocated, so your
+ *		shell implementation will most likely need to strdup() them to save.
+ *
+ *	endofname() - return the end of a variable name from input
+ *
+ *		The arithmetic code does not know about variable naming conventions.
+ *		So when it is given an experession, it knows something is not numeric,
+ *		but it is up to the shell to dictate what is a valid identifiers.
+ *		So when it encounters something like:
+ *			$(( some_var + 123 ))
+ *		It will make a call like so:
+ *			end = endofname("some_var + 123");
+ *		So the shell needs to scan the input string and return a pointer to the
+ *		first non-identifier string.  In this case, it should return the input
+ *		pointer with an offset pointing to the first space.  The typical
+ *		implementation will return the offset of first char that does not match
+ *		the regex (in C locale): ^[a-zA-Z_][a-zA-Z_0-9]*
+ */
+
+/* To make your life easier when dealing with optional 64bit math support,
+ * rather than assume that the type is "signed long" and you can always
+ * use "%ld" to scan/print the value, use the arith_t helper defines.  See
+ * below for the exact things that are available.
+ */
+
+#ifndef _SHELL_MATH_
+#define _SHELL_MATH_
+
+#if ENABLE_SH_MATH_SUPPORT_64
+typedef int64_t arith_t;
+#define arith_t_type long long
+#define arith_t_fmt "%lld"
+#define strto_arith_t strtoll
+#else
+typedef long arith_t;
+#define arith_t_type long
+#define arith_t_fmt "%ld"
+#define strto_arith_t strtol
+#endif
+
+typedef const char *(*arith_var_lookup_t)(const char *name);
+typedef void (*arith_var_set_t)(const char *name, const char *val, int flags);
+typedef char *(*arith_var_endofname_t)(const char *name);
+typedef struct arith_eval_hooks {
+	arith_var_lookup_t lookupvar;
+	arith_var_set_t setvar;
+	arith_var_endofname_t endofname;
+} arith_eval_hooks_t;
+
+arith_t arith(const char *expr, int *perrcode, arith_eval_hooks_t*);
+
+#endif