[ruby-dev:29061] Re: Numeric#step

|From: Tadayoshi Funaba <[e-mail]>
|Date: Mon, 17 Jul 2006 21:44:58 +0900

> Numeric#step ですが、1.0/0 = 無限大であるとき、
> 
> $ ruby -v -eInf=1.0/0 -e'1.step(Inf, Inf){|x| p x}'
> ruby 1.8.4 (2005-12-24) [i386-freebsd5.4]

> $ ruby -v -eInf=1.0/0 -e'10.step(1, Inf){|x| p x}'
> ruby 1.8.4 (2005-12-24) [i386-freebsd5.4]
> NaN

望ましい振舞いがどういうものかはわかりませんが、
Floatの場合にNaNが出るのはまずそうなので、
以下のような対処を考えました。
ついでにループカウンタが溢れる場合の対処もしています。
警告を出すかどうか/出し方はこれでよいかわかりませんが。

田中昌宏

--- numeric.c~	2006-05-01 12:46:46 +0900
+++ numeric.c	2006-07-18 21:05:38 +0900
@@ -1478,22 +1478,38 @@
     else if (TYPE(from) == T_FLOAT || TYPE(to) == T_FLOAT || TYPE(step) == T_FLOAT) {
 	const double epsilon = DBL_EPSILON;
 	double beg = NUM2DBL(from);
 	double end = NUM2DBL(to);
 	double unit = NUM2DBL(step);
 	double n = (end - beg)/unit;
 	double err = (fabs(beg) + fabs(end) + fabs(end-beg)) / fabs(unit) * epsilon;
 	long i;
+	int warn = 0;
 
+	if (isinf(beg) || isinf(unit)) {
+	    if ((unit>0 && (end-beg)>=0) || (unit<0 && (end-beg)<=0)) {
+	        unit = 0;
+	        n = 0;
+	    } else {
+	        n = -1;
+	    }
+	    err = 0;
+	}
 	if (err>0.5) err=0.5;
 	n = floor(n + err) + 1;
+	if (n>LONG_MAX) {
+	    n = LONG_MAX;
+	    warn = 1;
+	}
 	for (i=0; i<n; i++) {
 	    rb_yield(rb_float_new(i*unit+beg));
 	}
+	if (warn)
+	    rb_warn("iteration is reduced to LONG_MAX times");
     }
     else {
 	VALUE i = from;
 	ID cmp;
 
 	if (RTEST(rb_funcall(step, '>', 1, INT2FIX(0)))) {
 	    cmp = '>';
 	}


* ChangeLog

	* numeric.c (num_step): cares for Infifnity cases.
	  repeats at most LONG_MAX times in Float cases.


* 変更前動作

$ ./ruby -v
ruby 1.8.5 (2006-07-18) [i686-linux]
$ ./ruby -e'Inf=1.0/0; 1.step(Inf,1){|x| p x; break if x.abs>5}'
1.0
2.0
3.0
4.0
5.0
6.0
$ ./ruby -e'Inf=1.0/0; 1.step(Inf,-1){|x| p x; break if x.abs>5}'
$ ./ruby -e'Inf=1.0/0; 1.step(-Inf,1){|x| p x; break if x.abs>5}'
$ ./ruby -e'Inf=1.0/0; 1.step(-Inf,-1){|x| p x; break if x.abs>5}'
1.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
$ ./ruby -e'Inf=1.0/0;i=0; Inf.step(1,-1){|x| p x; break if (i+=1)>5}'
Infinity
Infinity
Infinity
Infinity
Infinity
Infinity
$ ./ruby -e'Inf=1.0/0;i=0; Inf.step(1,1){|x| p x; break if (i+=1)>5}'
$ ./ruby -e'Inf=1.0/0;i=0; (-Inf).step(1,-1){|x| p x; break if (i+=1)>5}'
$ ./ruby -e'Inf=1.0/0;i=0; (-Inf).step(1,1){|x| p x; break if (i+=1)>5}'
-Infinity
-Infinity
-Infinity
-Infinity
-Infinity
-Infinity
$ ./ruby -e'Inf=1.0/0; 1.step(10,Inf){|x| p x}'
NaN
$ ./ruby -e'Inf=1.0/0; 1.step(-10,Inf){|x| p x}'
NaN
$ ./ruby -e'Inf=1.0/0; 1.step(10,-Inf){|x| p x}'
NaN
$ ./ruby -e'Inf=1.0/0; 1.step(-10,-Inf){|x| p x}'
NaN
$ ./ruby -e'Inf=1.0/0; 1.step(1,Inf){|x| p x}'
NaN
$ ./ruby -e'Inf=1.0/0; 1.step(1,-Inf){|x| p x}'
NaN
$ ./ruby -e'Inf=1.0/0; 1.step(Inf,Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; 1.step(Inf,-Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; 1.step(-Inf,Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; 1.step(-Inf,-Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; Inf.step(Inf,Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; Inf.step(-Inf,Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; Inf.step(Inf,-Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; Inf.step(-Inf,-Inf){|x| p x}'


* 変更後動作

$ ./ruby -e'Inf=1.0/0; 1.step(Inf,1){|x| p x; break if x.abs>5}'1.0
2.0
3.0
4.0
5.0
6.0
$ ./ruby -e'Inf=1.0/0; 1.step(Inf,-1){|x| p x; break if x.abs>5}'
$ ./ruby -e'Inf=1.0/0; 1.step(-Inf,1){|x| p x; break if x.abs>5}'
$ ./ruby -e'Inf=1.0/0; 1.step(-Inf,-1){|x| p x; break if x.abs>5}'
1.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
$ ./ruby -e'Inf=1.0/0;i=0; Inf.step(1,-1){|x| p x; break if (i+=1)>5}'
Infinity
$ ./ruby -e'Inf=1.0/0;i=0; Inf.step(1,1){|x| p x; break if (i+=1)>5}'
$ ./ruby -e'Inf=1.0/0;i=0; (-Inf).step(1,-1){|x| p x; break if (i+=1)>5}'
$ ./ruby -e'Inf=1.0/0;i=0; (-Inf).step(1,1){|x| p x; break if (i+=1)>5}'
-Infinity
$ ./ruby -e'Inf=1.0/0; 1.step(10,Inf){|x| p x}'
1.0
$ ./ruby -e'Inf=1.0/0; 1.step(-10,Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; 1.step(10,-Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; 1.step(-10,-Inf){|x| p x}'
1.0
$ ./ruby -e'Inf=1.0/0; 1.step(1,Inf){|x| p x}'
1.0
$ ./ruby -e'Inf=1.0/0; 1.step(1,-Inf){|x| p x}'
1.0
$ ./ruby -e'Inf=1.0/0; 1.step(Inf,Inf){|x| p x}'
1.0
$ ./ruby -e'Inf=1.0/0; 1.step(Inf,-Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; 1.step(-Inf,Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; 1.step(-Inf,-Inf){|x| p x}'
1.0
$ ./ruby -e'Inf=1.0/0; Inf.step(Inf,Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; Inf.step(-Inf,Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; Inf.step(Inf,-Inf){|x| p x}'
$ ./ruby -e'Inf=1.0/0; Inf.step(-Inf,-Inf){|x| p x}'
Infinity