Feature #12172: Array#max and Array#min

• Status: Closed
• Assignee: mame (Yusuke Endoh)
• Target version: -

[mame (Yusuke Endoh)]

I propose to define Array#max. It is 10+ times faster than Enumerable#max since it skips a call to #each.

a = [*1..10000]; 100000.times { a.max }

• no patch: 22.424s
• Array#max defined: 1.740s

I don't think it is a good idea to copy all Enumerable methods to Array. But there are two reasons why max is special:

• It is one of the most basic operations for big data processing.
• We often use an idiom [a, b].max because of the lack of Math.max(a, b).

I think the latter is particularly important. The idiom is concise but unsuitable in a hotspot since it creates a temporal array. If Array#max is defined, we can easily optimize the idiom by introducing a special instruction like opt_newarray_max.

x, y = 1, 2; 10000000.times { [x, y].max }

• no patch: 2.799s
• Array#max defined: 1.224s
• opt_newarray_max: 0.555s

$ ./miniruby --dump=insns -e 'x, y = 1, 2; [x, y].max'
== disasm: #<ISeq:<main>@-e>============================================
local table (size: 3, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
[ 3] x          [ 2] y          
0000 trace            1                                               (   1)
0002 putobject_OP_INT2FIX_O_1_C_ 
0003 putobject        2
0005 setlocal_OP__WC__0 2
0007 setlocal_OP__WC__0 3
0009 getlocal_OP__WC__0 3
0011 getlocal_OP__WC__0 2
0013 opt_newarray_max 2
0015 leave

The patches are attached. (0001 is a preparation. 0002 introduces Array#max. 0003 introduces a special instruction.)

Of course, we can say the same for Array#min. The patches include Array#min too.

What do you think?

[mame (Yusuke Endoh)]

• Description updated (diff)

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to mame (Yusuke Endoh)

Matz and ko1 accepted this proposal. I'll commit.

[mame (Yusuke Endoh)]

• Status changed from Assigned to Closed

Applied in changeset r54150.

---

• array.c (rb_ary_max, rb_ary_min): Array#max and Array#min added.
  [Feature #12172]

• internal.h (OPTIMIZED_CMP): moved from enum.c so that array.c can
  use it.

• test/ruby/test_array.rb (test_max, test_min): tests for Array#max
  and Array#min.

• test/ruby/test_enum.rb (test_max, test_min): revised a bit to test
  Enumerable#max and #min explicitly.