Re^2: Maintain accuracy of floating point numbers in simple arithmetic operation

++Browser,

I must admit your solution takes the form of a brain teaser for me. I'll limit my query to the first thing that I can't figure out off the top of my head, which is why the + after the first set of parens? Isn't it redundant, given the + after the \d within?

In general, IMHO, I think an explanation of your solution would be helpful not only to me, but to others who may come across this thread, especially in the future, perhaps from a search.

EDIT: I guess what I don't understand is

The first thing with the +
Why test for $1 when the assumption is that there is always a digit before the decimal (w/ your program, Before '.6789%' becomes '.678900')

Note, that assumption is OK, for this application.

EDIT 2: I see now that the test is not for definedness, but for 0, because you don't want to make 0.779999% become 077.9999.

I like computer programming because it's like Legos for the mind.

Comment on Re^2: Maintain accuracy of floating point numbers in simple arithmetic operation

Replies are listed 'Best First'.
Re^3: Maintain accuracy of floating point numbers in simple arithmetic operation by BrowserUk (Patriarch) on Jun 13, 2007 at 16:44 UTC
... why the + after the first set of parens? Because I made a mistake and didn't notice because I was getting the right results. It is redundant and removing it makes no difference--'cept maybe it'll run a insy winsy bit quicker? :) There is a second 'artifact' in the replacement. `($1\|\|'')` can become just `$1`. I was attempting to avoid the need to suppress warnings, but it turns the code it a mess of bracketed \|\|s and ternaries; or a long if then else chain. Warnings are optional and turning them off, as an informed decision to avoid complicated code, is (IMO) legit. So I chose the cleaner option. You can replace `local $^W;` with `no warnings 'uninitialised';` or the chain of defined and length tests if you prefer. Does this explain it? #! perl -slw use strict; while( <DATA> ) { chomp; printf "Before '%s' becomes ", $_; s[ ( \d+ ) ## Grab any digits before a decimal point (?: \. ## If there is a decimal point ( \d{0,2} ) ## Try grab two digits after it ( \d* ) ## And any more into another capture )? ## All conditionally % ## And finally... ]{ local $^W; ## I know some of the captures will be emp +ty. ## Pad (trailing zeros) the digits being moved to ensure exact +ly 2 my $n = substr( $2 . '00', 0, 2 ); ## Reassemble the number from ## Any digits previously before the decimal point ## The two digits being moved ## A decimal point and the remaining digits if there are +any. $1 . $n . ( length($3) ? ".$3" : '' ); }xe; print "'$_'"; } __DATA__ [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l] [select]
Re^3: Maintain accuracy of floating point numbers in simple arithmetic operation by BrowserUk (Patriarch) on Jun 13, 2007 at 19:10 UTC
Updates after the fact will often not be noticed unless you /msg the intended recipient. I used your tests which did not include a '.nnn%' example so that possibility didn't get tested. If you were my boss, I would probably deserve admonishment. This, as with most posts, is intended to give you ideas for solving your problem, not a fully tested piece of code that you can drop into you codebase for free.	[reply]