[Python-Dev] C Decimal - is there any interest?

[Mateusz Rukowicz]

Mateusz Rukowicz wrote:

>Hi!
>
>    I've been working on C decimal project during gSoC 2006. After year 
>of idling (I had extremely busy first year on University, but well, most 
>of us are extremely busy) I decided, that I will handle further 
>developing (there is still much development needed, and updating to most 
>recent standard is just the beginning). I understand, that chances of 
>merging C Decimal with main tree are much lower than year ago, so I 
>would like to know if there is still interest in C version of Decimal. 
>If so - should I write PEP, or just code and 'we'll see later'?
>
>I've made a little benchmark - given loan amount, assets and months that 
>it's meant to be payed off, find minimal monthly loan cost (It's just 
>first idea that came to me for use Decimal in financial 'application' 
>:>) [This solution has complexity O(log(amount) * months) which is far 
>from optimal, but it's meant to benchmark Decimal, not python itself].
>
>Code:
>
>from _decimal import *
>import sys
>gc = getcontext();
>
>def check(loan, percent, monthly):
>    ret = 0
>    mult = 1 + (percent / 1200)
>    if (loan - monthly) * mult >= loan:
>        return -1               #you cannot payoff loan ;(
>
>    while loan > 0:
>        loan = loan - monthly
>        loan = loan * mult
>        ret += 1
>    return ret
>
>def minimize_monthly(loan, percent, months):
>    lower = Decimal(0)
>    upper = Decimal(loan)
>
>    while(upper > lower + Decimal("1e-3")):
>        mid = (upper + lower)/2
>        ret = check(loan, percent, mid)
>        if(ret > months or ret == -1):
>            lower = mid
>        else:
>            upper = mid
>
>
>    return lower
>
>
>
>gc.prec = int(sys.argv[4])
>gc.rounding = ROUND_UP
>print minimize_monthly(Decimal(sys.argv[1]), Decimal(sys.argv[2]), 
>int(sys.argv[3]))
>
>and timings (1mln loan, for 15 years, 2% year assets, and precision = 10 
>:>):
>mateusz at MatLaps:~/programy/python/decimal/decimal-c$ time 
>../../pyth/python/python loan.py  1000000 2 180 10
>6424.37955
>
>real    0m0.068s
>user    0m0.064s
>sys     0m0.004s
>mateusz at MatLaps:~/programy/python/decimal/decimal-c$ time 
>../../pyth/python/python loan2.py  1000000 2 180 10
>6424.37955
>
>real    0m2.168s
>user    0m2.148s
>sys     0m0.016s
>
>Please don't misunderstand me - I don't want to show python Decimal is 
>slow, I want to show that C Decimal is worth effort. I am also aware of 
>simplicity of this benchmark. (This python have been of course compiled 
>with -O3).
>
>Best regards,
>Mateusz Rukowicz.
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>  
>
Sorry for two messages, thunderbird told me first message hadn't been send.