4 ms·

Yeah, Python is one of the few languages which actually defines sane behavior for integer division and modulus rather than leaving it up to the hardware. I wis

by panic 8y ago

Yeah, Python is one of the few languages which actually defines sane behavior for integer division and modulus rather than leaving it up to the hardware. I wish more languages would follow its example!

triska 8y ago
Prolog is also like this: ?- x is -4 mod 2. X = 0. ?- X is -8 mod 2. X = 0. ?- X is -9 mod 2. X = 1. Using declarative integer arithmetic, we can even express very generally that a number X is a multiple of 2: ?- X #= 2*_. This is true iff there is any integer (indicated by an anonymous variable _) that, multiplied by 2, yields X. It works for positive and negative integers. For example: ?- -4 #= 2*_. true. ?- -9 #= 2*_. false. A very nice reference on the general topic of bitwise operations is Donald Knuth's Bitwise Tricks and Techniques in Volume 4 of The Art of Computer Programming.
bakery2k 8y ago
Guido has written a blog post explaining "Why Python's Integer Division Floors" [1]. Python also uses floor division, and the corresponding "sign-of-modulo matches sign-of-divisor", for floating-point numbers. The blog post claims that this can be problematic in certain cases (compared to C's "sign-of-modulo matches sign-of-dividend"), but does not give any concrete examples. [1] http://python-history.blogspot.com.au/2010/08/why-pythons-integer-division-floors.html http://python-history.blogspot.com.au/2010/08/why-pythons-in...
kazinator 8y ago
ISO C doesn't leave it up to the hardware. Integer division is required to truncate toward zero; the remainder harmonizes with that. (If someone designs a new HLL which leaves some arithmetic to the hardware that C doesn't, that is indeed silly.) The sane language here Common Lisp: it does it in all the ways rather than picking one approach with some hand-waving justification about why it's the good choice. It has truncate, round, ceiling and floor functions that all return a quotient and remainder. There are also mod and rem functions that calculate just the remainder from a floor and truncate, respectively.

by panic 8y ago

triska 8y ago

Prolog is also like this: ?- x is -4 mod 2. X = 0. ?- X is -8 mod 2. X = 0. ?- X is -9 mod 2. X = 1. Using declarative integer arithmetic, we can even express very generally that a number X is a multiple of 2: ?- X #= 2*_. This is true iff there is any integer (indicated by an anonymous variable _) that, multiplied by 2, yields X. It works for positive and negative integers. For example: ?- -4 #= 2*_. true. ?- -9 #= 2*_. false. A very nice reference on the general topic of bitwise operations is Donald Knuth's Bitwise Tricks and Techniques in Volume 4 of The Art of Computer Programming.

bakery2k 8y ago

Guido has written a blog post explaining "Why Python's Integer Division Floors" [1]. Python also uses floor division, and the corresponding "sign-of-modulo matches sign-of-divisor", for floating-point numbers. The blog post claims that this can be problematic in certain cases (compared to C's "sign-of-modulo matches sign-of-dividend"), but does not give any concrete examples. [1] http://python-history.blogspot.com.au/2010/08/why-pythons-integer-division-floors.html http://python-history.blogspot.com.au/2010/08/why-pythons-in...

kazinator 8y ago

ISO C doesn't leave it up to the hardware. Integer division is required to truncate toward zero; the remainder harmonizes with that. (If someone designs a new HLL which leaves some arithmetic to the hardware that C doesn't, that is indeed silly.) The sane language here Common Lisp: it does it in all the ways rather than picking one approach with some hand-waving justification about why it's the good choice. It has truncate, round, ceiling and floor functions that all return a quotient and remainder. There are also mod and rem functions that calculate just the remainder from a floor and truncate, respectively.