* bignum.c (big2str_2bdigits): reduce div instruction.

Fix the code so that C compiler unify div instructions of `%` and `/`.

Before:
  4291b0:       48 89 f0                mov    %rsi,%rax
  4291b3:       31 d2                   xor    %edx,%edx
  4291b5:       48 83 ef 01             sub    $0x1,%rdi
  4291b9:       48 f7 f1                div    %rcx  # <---- !
  4291bc:       41 0f b6 04 11          movzbl (%r9,%rdx,1),%eax
  4291c1:       31 d2                   xor    %edx,%edx
  4291c3:       41 88 04 38             mov    %al,(%r8,%rdi,1)
  4291c7:       48 63 4b 04             movslq 0x4(%rbx),%rcx
  4291cb:       48 89 f0                mov    %rsi,%rax
  4291ce:       48 f7 f1                div    %rcx  # <---- !
  4291d1:       48 89 c6                mov    %rax,%rsi
  4291d4:       48 85 ff                test   %rdi,%rdi
  4291d7:       75 d7                   jne    4291b0 <big2str_2bdigits+0x50>
  4291d9:       48 63 6b 10             movslq 0x10(%rbx),%rbp
  4291dd:       48 01 6b 20             add    %rbp,0x20(%rbx)
  4291e1:       48 8b 44 24 48          mov    0x48(%rsp),%rax
  4291e6:       64 48 33 04 25 28 00    xor    %fs:0x28,%rax

After:
  4291b0:       48 63 73 04             movslq 0x4(%rbx),%rsi
  4291b4:       31 d2                   xor    %edx,%edx
  4291b6:       48 83 e9 01             sub    $0x1,%rcx
  4291ba:       48 f7 f6                div    %rsi  # <---- !
  4291bd:       41 0f b6 14 10          movzbl (%r8,%rdx,1),%edx
  4291c2:       88 14 0f                mov    %dl,(%rdi,%rcx,1)
  4291c5:       48 85 c9                test   %rcx,%rcx
  4291c8:       75 e6                   jne    4291b0 <big2str_2bdigits+0x50>
  4291ca:       48 63 6b 10             movslq 0x10(%rbx),%rbp
  4291ce:       48 01 6b 20             add    %rbp,0x20(%rbx)
  4291d2:       48 8b 44 24 48          mov    0x48(%rsp),%rax
  4291d7:       64 48 33 04 25 28 00    xor    %fs:0x28,%rax

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54102 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,7 @@
+Mon Mar 14 19:05:39 2016  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* bignum.c (big2str_2bdigits): reduce div instruction.
+
 Mon Mar 14 18:39:53 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* include/ruby/oniguruma.h, enc/unicode.c: Adjusting flag assignments

bignum.c

@@ -4615,8 +4615,9 @@ big2str_2bdigits(struct big2str_struct *b2s, BDIGIT *xds, size_t xn, size_t tail
         p = buf;
         j = sizeof(buf);
         do {
-            p[--j] = ruby_digitmap[num % b2s->base];
+            BDIGIT_DBL idx = num % b2s->base;
             num /= b2s->base;
+            p[--j] = ruby_digitmap[idx];
         } while (num);
         len = sizeof(buf) - j;
         big2str_alloc(b2s, len + taillen);
@@ -4626,8 +4627,9 @@ big2str_2bdigits(struct big2str_struct *b2s, BDIGIT *xds, size_t xn, size_t tail
         p = b2s->ptr;
         j = b2s->hbase2_numdigits;
         do {
-            p[--j] = ruby_digitmap[num % b2s->base];
+            BDIGIT_DBL idx = num % b2s->base;
             num /= b2s->base;
+            p[--j] = ruby_digitmap[idx];
         } while (j);
         len = b2s->hbase2_numdigits;
     }