mrkn	2013-11-23 19:49:36 +0900 (Sat, 23 Nov 2013)

  New Revision: 43816

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=rev&revision=43816

  Log:
    exp

  Modified files:
    trunk/ChangeLog
    trunk/ext/bigdecimal/bigdecimal.c
Index: ChangeLog
===================================================================
--- ChangeLog	(revision 43815)
+++ ChangeLog	(revision 43816)
@@ -1,3 +1,10 @@ https://github.com/ruby/ruby/blob/trunk/ChangeLog#L1
+Sat Nov 23 19:46:00 2013  Kenta Murata  <mrkn@m...>
+
+	* ext/bigdecimal/bigdecimal.c (BigMath_s_exp): Optimize the
+	  calculation algorithm to reduce the number of divisions.
+	  This optimization was proposed by Rafa Michalski.
+	  [Feature #6857] [ruby-core:47130]
+
 Sat Nov 23 19:20:00 2013  Kenta Murata  <mrkn@m...>
 
 	* ext/bigdecimal/bigdecimal.c (BigDecimal_div2): The signature was
Index: ext/bigdecimal/bigdecimal.c
===================================================================
--- ext/bigdecimal/bigdecimal.c	(revision 43815)
+++ ext/bigdecimal/bigdecimal.c	(revision 43816)
@@ -2675,7 +2675,7 @@ BigMath_s_exp(VALUE klass, VALUE x, VALU https://github.com/ruby/ruby/blob/trunk/ext/bigdecimal/bigdecimal.c#L2675
 {
     ssize_t prec, n, i;
     Real* vx = NULL;
-    VALUE one, d, x1, y, z;
+    VALUE one, d, y;
     int negative = 0;
     int infinite = 0;
     int nan = 0;
@@ -2751,11 +2751,9 @@ BigMath_s_exp(VALUE klass, VALUE x, VALU https://github.com/ruby/ruby/blob/trunk/ext/bigdecimal/bigdecimal.c#L2751
     }
 
     one = ToValue(VpCreateRbObject(1, "1"));
-    x1  = one;
     y   = one;
     d   = y;
-    z   = one;
-    i   = 0;
+    i   = 1;
 
     while (!VpIsZero((Real*)DATA_PTR(d))) {
 	SIGNED_VALUE const ey = VpExponent10(DATA_PTR(y));
@@ -2771,11 +2769,10 @@ BigMath_s_exp(VALUE klass, VALUE x, VALU https://github.com/ruby/ruby/blob/trunk/ext/bigdecimal/bigdecimal.c#L2769
 	    m = rmpd_double_figures();
 	}
 
-	x1 = BigDecimal_mult2(x1, x, SSIZET2NUM(n));
-	++i;
-	z = BigDecimal_mult(z, SSIZET2NUM(i));
-	d = BigDecimal_div2(x1, z, SSIZET2NUM(m));
-	y = BigDecimal_add(y, d);
+	d = BigDecimal_mult(d, x);                             /* d <- d * x */
+	d = BigDecimal_div2(d, SSIZET2NUM(i), SSIZET2NUM(m));  /* d <- d / i */
+	y = BigDecimal_add(y, d);                              /* y <- y + d  */
+	++i;                                                   /* i  <- i + 1 */
     }
 
     if (negative) {
@@ -2788,10 +2785,8 @@ BigMath_s_exp(VALUE klass, VALUE x, VALU https://github.com/ruby/ruby/blob/trunk/ext/bigdecimal/bigdecimal.c#L2785
 
     RB_GC_GUARD(one);
     RB_GC_GUARD(x);
-    RB_GC_GUARD(x1);
     RB_GC_GUARD(y);
     RB_GC_GUARD(d);
-    RB_GC_GUARD(z);
 }
 
 /* call-seq:

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