float-eval-bash-builtins

A bash builtins which evaluate a arithmetic expression (as a string) and return a double (+/- what GNU bc does).

Build

Just do a make to build the builtin.

If you want to build a static binary (to simply call it with something like ./float_eval "<expr>"), you do a make static=1.

In either cases, you can enable debug with: make debug=1.

Use

Run enable -f ./float_eval.so float_eval (you'll have to repeat this command in each shell). You can use the absolute path near ./float_eval.so to use it anywhere (or put it in an alias)

You can now use float_eval "1+2" and you'll get the result in $REPLY.

You can ask for several calculations at once float_eval "1+2" "2*3" "8%3" and $REPLY will store them as an array (REPLY[0]=3 REPLY[1]=6 REPLY[2]=2).

Supported operations

You can use every common operations :

• + - * / and % (modulo)
• bitwise operators | & ^ and bitwise shifts << >>
• expression in parentheses (...) (may be on several levels (3 * (1+2)))
• comparaisons == != < <= > >=
• combinaisons || &&
• Not !
• Bitwise not ~
• Exponentiation (pow) **
• Set wanted precision (-p INTEGER)
• Scientific notation 1.00E+003
• Error handling: On invalid input, the binary/builtin return 1
• Long input lines (dynamically allocated)
• Numbers are coded on 256 bits using the MPFR library (http://www.mpfr.org/)

Note that comparaisons and combinaisons results in a boolean : 1 == true and 0 == false

Scientific notation is a decimal number (possibly with a dot) followed by an 'E' or 'e', optionally followed with a plus or minus sign, followed by decimal digits. It indicates multiplication by a power of 10 (cf man of strtod).

You can look test.sh to see all operations and their combinaisons that are known to work.

Not yet supported

• Syntax check

Benchmarks

You can do a simple benchmark by executing ./test.sh (it will also check that the builtin's behavior is as expected).

It will compare the performances of the builtin and a bash function using bc on 1k iterations (you can change that by setting $NB in the environment NB=10000 ./test.sh).

In my tests, the bash version is +/- 100 time slower than the builtin (200 if one builtin call). For 100k calls :

• Builtin : 1.076
• Builtin (with one call of 100k args) : 0.439
• Bash (bc) : 98.531s

Notes

I added a directory bash-headers-4.1.2-9.el6_2.x86_64 (as provided in CentOS 6) with all bash's headers. Feel free to test with another version, it shouldn't be a problem.