Feature #12172


Array#max and Array#min

Added by mame (Yusuke Endoh) about 8 years ago. Updated about 8 years ago.

Target version:


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?


Updated by mame (Yusuke Endoh) about 8 years ago

  • Description updated (diff)

Updated by mame (Yusuke Endoh) about 8 years ago

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

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

Actions #3

Updated by mame (Yusuke Endoh) about 8 years ago

  • 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.


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