Hi all!
I submitted the following to
http://rubyforge.org/tracker/index.php?func=deta
il&aid=14051
&group_id=426&atid=1700
Numeric#divmod (numeric.c line 264-302)
========================================
1. There is an error in the table in column a/b: 13/-4 is
-4, not -3!
C:Dokume~1All UsersDokume~1>irb
irb(main):001:0> RUBY_VERSION #=>
"1.8.6"
irb(main):002:0> 13/-4 #=> -4
<=!
2. The divmod formula
a. is given in C and not Ruby terms,
b. should use the same parameter names as the table and
c. is wrong: Numeric does not convert a and b to floats.
The division
with "/" is handled by the
respective subclasses and they
do it differently depending on the class of
num.
So, it would be correct and Ruby-esk to write:
* Returns an array containing the quotient and modulus
obtained by
* dividing <i>num</i> by
<i>aNumeric</i>.
* If
* q, r = a.divmod(b)
* then
* q = (a/b).floor
* r = a.modulo(b) = a - q*b
3. For didactical reasons I would also propose to change
the table layout:
* | a.divmod(b) |
* a | b | a/b | (a/b).floor, a.modulo(b) |
a.remainder(b)
*
------+-----+--------+---------------------------+----------
-----
* 13 | 4 | 3 | 3 , 1 |
1
*
------+-----+--------+---------------------------+----------
-----
* 13 | -4 | -4 | -4 , -3 |
1
*
------+-----+--------+---------------------------+----------
-----
instead of
* a | b | a.divmod(b) | a/b | a.modulo(b) |
a.remainder(b)
*
------+-----+---------------+---------+-------------+-------
--------
* 13 | 4 | 3, 1 | 3 | 1 |
1
*
------+-----+---------------+---------+-------------+-------
--------
* 13 | -4 | -4, -3 | -3 | -3 |
1
*
------+-----+---------------+---------+-------------+-------
--------
Altogether my corrections and proposals sum up to:
------------------------------------------------------------
--------------
/*
* call-seq:
* num.divmod( aNumeric ) => anArray
*
* Returns an array containing the quotient and modulus
obtained by
* dividing <i>num</i> by
<i>aNumeric</i>.
* If
* q, r = a.divmod(b)
* then
* q = (a/b).floor
* r = a.modulo(b) = a - q*b
*
* The quotient is rounded toward -infinity, as shown in
the following
table:
*
* | a.divmod(b) |
* a | b | a/b | (a/b).floor, a.modulo(b) |
a.remainder(b)
*
------+-----+--------+---------------------------+----------
-----
* 13 | 4 | 3 | 3 , 1 |
1
*
------+-----+--------+---------------------------+----------
-----
* 13 | -4 | -4 | -4 , -3 |
1
*
------+-----+--------+---------------------------+----------
-----
* -13 | 4 | -4 | -4 , 3 |
-1
*
------+-----+--------+---------------------------+----------
-----
* -13 | -4 | 3 | 3 , -1 |
-1
*
------+-----+--------+---------------------------+----------
-----
* 11.5 | 4 | 2.875 | 2 , 3.5 |
3.5
*
------+-----+--------+---------------------------+----------
-----
* 11.5 | -4 | -2.875 | -3 , -0.5 |
3.5
*
------+-----+--------+---------------------------+----------
-----
* -11.5 | 4 | -2.875 | -3 , 0.5 |
-3.5
*
------+-----+--------+---------------------------+----------
-----
* -11.5 | -4 | 2.875 | 2 , -3.5 |
-3.5
*
*
* Examples
* 11.divmod(3) #=> [3, 2]
* 11.divmod(-3) #=> [-4, -1]
* 11.divmod(3.5) #=> [3, 0.5]
* (-11.5).divmod(3.5) #=> [-4, 2.5]
* Rational(7,4).divmod Rational(1,2) #=> [3,
Rational(1,4)]
*/
------------------------------------------------------------
--------------
instead of the old:
------------------------------------------------------------
--------------
/*
* call-seq:
* num.divmod( aNumeric ) -> anArray
*
* Returns an array containing the quotient and modulus
obtained by
* dividing <i>num</i> by
<i>aNumeric</i>. If <code>q, r =
* x.divmod(y)</code>, then
*
* q = floor(float(x)/float(y))
* x = q*y + r
*
* The quotient is rounded toward -infinity, as shown in
the following
table:
*
* a | b | a.divmod(b) | a/b | a.modulo(b) |
a.remainder(b)
*
------+-----+---------------+---------+-------------+-------
--------
* 13 | 4 | 3, 1 | 3 | 1 |
1
*
------+-----+---------------+---------+-------------+-------
--------
* 13 | -4 | -4, -3 | -3 | -3 |
1
*
------+-----+---------------+---------+-------------+-------
--------
* -13 | 4 | -4, 3 | -4 | 3 |
-1
*
------+-----+---------------+---------+-------------+-------
--------
* -13 | -4 | 3, -1 | 3 | -1 |
-1
*
------+-----+---------------+---------+-------------+-------
--------
* 11.5 | 4 | 2, 3.5 | 2.875 | 3.5 |
3.5
*
------+-----+---------------+---------+-------------+-------
--------
* 11.5 | -4 | -3, -0.5 | -2.875 | -0.5 |
3.5
*
------+-----+---------------+---------+-------------+-------
--------
* -11.5 | 4 | -3, 0.5 | -2.875 | 0.5 |
-3.5
*
------+-----+---------------+---------+-------------+-------
--------
* -11.5 | -4 | 2, -3.5 | 2.875 | -3.5 |
-3.5
*
*
* Examples
* 11.divmod(3) #=> [3, 2]
* 11.divmod(-3) #=> [-4, -1]
* 11.divmod(3.5) #=> [3, 0.5]
* (-11).divmod(3.5) #=> [-4, 3.0]
* (11.5).divmod(3.5) #=> [3, 1.0]
*/
------------------------------------------------------------
--------------
The patch to numeric.c is attached.
Regards,
Dirk
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