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Re: Fast conversion of numbers to numerator/denominator pairs

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On 24 August 2013 13:30, Steven D'Aprano <
steve+comp.lang.python@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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Thread

Fast conversion of numbers to numerator/denominator pairs Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-24 03:30 +0000
  Re: Fast conversion of numbers to numerator/denominator pairs Ian Kelly <ian.g.kelly@gmail.com> - 2013-08-24 01:37 -0600
  Re: Fast conversion of numbers to numerator/denominator pairs Ian Kelly <ian.g.kelly@gmail.com> - 2013-08-24 01:50 -0600
  Re: Fast conversion of numbers to numerator/denominator pairs Peter Otten <__peter__@web.de> - 2013-08-24 14:52 +0200
  Re: Fast conversion of numbers to numerator/denominator pairs Tim Delaney <timothy.c.delaney@gmail.com> - 2013-08-25 07:59 +1000
  Re: Fast conversion of numbers to numerator/denominator pairs Tim Delaney <timothy.c.delaney@gmail.com> - 2013-08-25 08:05 +1000

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