Fast conversion of numbers to numerator/denominator pairs

[Tim Delaney]

On 24 August 2013 13:30, Steven D'Aprano <
steve+comp.lang.python at pearwood.info> wrote:

>
> def convert(d):
>     sign, digits, exp = d.as_tuple()
>     num = int(''.join([str(digit) for digit in digits]))
>     if sign: num = -num
>     return num, 10**-exp
>
> which is faster, but not fast enough. Any suggestions?
>

Straightforward multiply and add takes about 60% of the time for a single
digit on my machine compared to the above, and 55% for 19 digits (so
reasonably consistent). It's about 10x slower than fractions.

def convert_muladd(d, _trans=_trans, bytes=bytes):
    sign, digits, exp = d.as_tuple()
    num = 0

    for digit in digits:
        num *= 10
        num += digit

    if sign:
        num = -num

    return num, 10**-exp

Breakdown of the above (for 19 digits):

d.as_tuple() takes about 35% of the time.

The multiply and add takes about 55% of the time.

The exponentiation takes about 10% of the time.

Tim Delaney
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