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Re: Division in Smalltalk
- To: LRG^ at PARC-MAXC, Goldstein at PARC-MAXC, Bobrow at PARC-MAXC
- Subject: Re: Division in Smalltalk
- From: Deutsch at PARC-MAXC
- Date: Wed ,31 Dec 80 15:52:00 EDT
- Cc: LISP-FORUM at MIT-MC
Well, it looks like we've finally come to a decision about the
division and remainder (modulus) operators in Smalltalk-80, so here it
is for everyone to start getting used to it.
/ means "correct division". If you divide two integers and the
remainder wouldn't be zero, / returns a Fraction (rational
representation in lowest terms). If you divide two exact numbers
(integers or Fractions), the result loses no information: it is a
Fraction if (and only if) the quotient isn't integral. If you do a
division involving an inexact number (Float), the result is always a
// means "division with truncation towards minus infinity". The
result is always an integer, regardless of what you started with. a
// b is equivalent to (a / b) floor.
\\ means "remainder with truncation towards minus infinity". a
\\ b is equivalent to a - ((a // b) * b). This operation is sometimes
called "modulus": it is, for example, an appropriate operation for
reducing hash values modulo a table size.
quo: means "division with truncation towards zero". The result is
always an integer. a quo: b is equivalent to (a / b) truncate.
rem: means "remainder with truncation towards zero", i.e. a rem: b is
equivalent to a - ((a quo: b) * b).
This arrangement was worked out in a long and often frustrating
process that involved input from a lot of people. Steve Putz is
busily implementing it at this very moment.