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