long(Decimal) performance

[ajaksu]

Hi Aahz, thanks for the feedback!

Aahz wrote:
> I'm not sure why it's coded that, but it's somewhat irrelevant: right
> now, work is being done to convert decimal.py to C code, which will
> almost certainly be much faster than your code.  Generally speaking, you
> should not be using Decimal now with any expectation of speed.

Agreed and agreed.

Just to avoid that the buggy (and unreadable) versions above harm
anyone, here's a better attempt:

def dec2long(number):
    """ Convert C{decimal.Decimal} to long """
    decimal_string = str(number)
    ## Split 123.45E10 -> radix = 123.45, exponent = 10
    if "e" in decimal_string:
        radix, exponent = decimal_string.split("e")
    elif "E" in decimal_string:
        radix, exponent = decimal_string.split("E")
    else:
        radix, exponent = (decimal_string, 0)
    if exponent:
        exponent = int(exponent)
        if "." in radix:
            ## radix = 123.45, radix_decimal_part_len = 2
            radix_decimal_part_len = long(len(radix.split(".")[1]))
            ## radix = 123.45, radix_as_long = 123.45 * 10**2 = 12345
            radix_as_long = long(Decimal(radix) *
(10L**radix_decimal_part_len))
            ##corrected_exponent = 10 - 2 = 8
            corrected_exponent = exponent - radix_decimal_part_len
            ## return 12345 * 10**8
            result =  radix_as_long * 10L** corrected_exponent
        else:
            radix_as_long = long(radix)
            result = radix_as_long * 10L**exponent
    else:
        if "." in radix:
            radix_integer_part = long(radix.split(".")[0])
        else:
            radix_integer_part = long(radix)
        result = radix_integer_part
    return result


Working from inside decimal.py allows things to work faster, but anyone
wanting speed REALLY shouldn't use Decimal :). Now I'm trying clnum
("Rational and arbitrary precision floating point numbers"):
http://cheeseshop.python.org/pypi/clnum/1.2

Cheers,
Daniel