From: Nobuyoshi Nakada <nobu@...>
Date: 2009-03-03T04:00:56+09:00
Subject: [ruby-core:22630] Re: suggestions for float

Hi,

At Mon, 2 Mar 2009 22:51:50 +0900,
Heesob Park wrote in [ruby-core:22623]:
> In my test with ruby float, %.14g is not enough, %.20g is suitable.
> It will written with Ruby code as like this:

Marshal also has such code.


Index: numeric.c
===================================================================
--- numeric.c	(revision 22706)
+++ numeric.c	(working copy)
@@ -522,5 +522,7 @@ static VALUE
 flo_to_s(VALUE flt)
 {
-    char buf[32];
+    enum {decimal_mant = DBL_MANT_DIG-DBL_DIG};
+    enum {float_dig = DBL_DIG+2};
+    char buf[float_dig + (decimal_mant + CHAR_BIT - 1) / CHAR_BIT + 10];
     double value = RFLOAT_VALUE(flt);
     char *p, *e;
@@ -531,10 +533,10 @@ flo_to_s(VALUE flt)
 	return rb_usascii_str_new2("NaN");
 
-    snprintf(buf, sizeof(buf), "%#.15g", value); /* ensure to print decimal point */
+    snprintf(buf, sizeof(buf), "%#.*g", float_dig, value); /* ensure to print decimal point */
     if (!(e = strchr(buf, 'e'))) {
 	e = buf + strlen(buf);
     }
     if (!ISDIGIT(e[-1])) { /* reformat if ended with decimal point (ex 111111111111111.) */
-	snprintf(buf, sizeof(buf), "%#.14e", value);
+	snprintf(buf, sizeof(buf), "%#.*e", float_dig - 1, value);
 	if (!(e = strchr(buf, 'e'))) {
 	    e = buf + strlen(buf);


-- 
Nobu Nakada