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Feature #12244

Updated by naruse (Yui NARUSE) over 3 years ago

We sometimes calculates `integer - integer % num`.

For example time series events into time partitions, we write code like

```ruby
event # {time: 1459580435, name: "hoge", text: "Rawr!"}
partition = event[:time] - event[:time] % num
chunk = get_chunk(partition)
chunk.write event
```
https://twitter.com/tagomoris/status/715814050534461440
https://twitter.com/tagomoris/status/715814961260457985

The name is always issue.
There are some suggestions likes Integer#adjust](https://twitter.com/cocoatomo/status/716088708655489024).

kosaki says [Excel's FLOOR() function is FLOOR(number, significance)](https://twitter.com/kosaki55tea/status/716059296186765312).
Therefore Ruby should be [Integer#floor(digits=1, significance: nil)](https://twitter.com/kosaki55tea/status/716106530114768897).
[kosaki agrees this](https://twitter.com/kosaki55tea/status/716107516409581568).

I checked the speed of a half baked implementation..., but it's 10x slow...


```
% time ./miniruby -e'i=10000000;while i>0;i-=1;1459497599.floor(significance: 3600);end'
./miniruby 6.58s user 0.02s system 99% cpu 6.596 total
#3 1459604131 22:35:31 naruse@windy:~/obj/ruby
% time ./miniruby -e'i=10000000;while i>0;i-=1;t=1459497599;t-t%3600;end'
./miniruby -e'i=10000000;while i>0;i-=1;t=1459497599;t-t%3600;end' 0.52s user 0.00s system 99% cpu 0.520 total
```

```diff
diff --git a/numeric.c b/numeric.c
index 37217a1..f6acfe3 100644
--- a/numeric.c
+++ b/numeric.c
@@ -4123,6 +4123,42 @@ int_dotimes(VALUE num)

/*
* call-seq:
+ * int.floor([ndigits]) -> integer or float
+ *
+ * Rounds +int+ to a given precision in decimal digits (default 0 digits).
+ *
+ * Precision may be negative. Returns a floating point number when +ndigits+
+ * is positive, +self+ for zero, and round down for negative.
+ *
+ * 1.round #=> 1
+ * 1.round(2) #=> 1.0
+ * 15.round(-1) #=> 20
+ */
+
+static VALUE
+int_floor(int argc, VALUE* argv, VALUE num)
+{
+ static ID keyword_ids[1];
+ VALUE kwargs[1], ndigits, opt;
+ if (!keyword_ids[0]) {
+ CONST_ID(keyword_ids[0], "significance");
+ }
+
+ rb_scan_args(argc, argv, "01:", &ndigits, &opt);
+ if (!NIL_P(opt)) {
+ VALUE factor;
+ long a, b;
+ rb_get_kwargs(opt, keyword_ids, 0, 1, kwargs);
+ factor = kwargs[0];
+ a = FIX2LONG(num);
+ b = FIX2LONG(factor);
+ return LONG2FIX(a - a % b);
+ }
+ return Qnil;
+}
+
+/*
+ * call-seq:
* int.round([ndigits]) -> integer or float
*
* Rounds +int+ to a given precision in decimal digits (default 0 digits).
@@ -4321,7 +4357,7 @@ Init_Numeric(void)
rb_define_method(rb_cInteger, "to_i", int_to_i, 0);
rb_define_method(rb_cInteger, "to_int", int_to_i, 0);
rb_define_method(rb_cInteger, "to_f", int_to_f, 0);
- rb_define_method(rb_cInteger, "floor", int_to_i, 0);
+ rb_define_method(rb_cInteger, "floor", int_floor, -1);
rb_define_method(rb_cInteger, "ceil", int_to_i, 0);
rb_define_method(rb_cInteger, "truncate", int_to_i, 0);
rb_define_method(rb_cInteger, "round", int_round, -1);

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