diff --git a/ChangeLog b/ChangeLog
index 9fadd570a2..1623eb4b1e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu May 13 13:30:05 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* marshal.c (w_float): use minimal representation.
+
+	* numeric.c (ruby_dbl2cstr): split from rb_float_new.
+
 Thu May 13 13:09:24 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* vm_core.h (rb_vm_get_sourceline): moved from eval_intern.h for
diff --git a/marshal.c b/marshal.c
index 702dd66357..857dd7361c 100644
--- a/marshal.c
+++ b/marshal.c
@@ -245,6 +245,8 @@ w_bytes(const char *s, long n, struct dump_arg *arg)
     w_nbyte(s, n, arg);
 }
 
+#define w_cstr(s, arg) w_bytes(s, strlen(s), arg)
+
 static void
 w_short(int x, struct dump_arg *arg)
 {
@@ -308,35 +310,6 @@ w_long(long x, struct dump_arg *arg)
 #define MANT_BITS 8
 #endif
 
-static int
-save_mantissa(double d, char *buf)
-{
-    int e, i = 0;
-    unsigned long m;
-    double n;
-
-    d = modf(ldexp(frexp(fabs(d), &e), DECIMAL_MANT), &d);
-    if (d > 0) {
-	buf[i++] = 0;
-	do {
-	    d = modf(ldexp(d, MANT_BITS), &n);
-	    m = (unsigned long)n;
-#if MANT_BITS > 24
-	    buf[i++] = (char)(m >> 24);
-#endif
-#if MANT_BITS > 16
-	    buf[i++] = (char)(m >> 16);
-#endif
-#if MANT_BITS > 8
-	    buf[i++] = (char)(m >> 8);
-#endif
-	    buf[i++] = (char)m;
-	} while (d > 0);
-	while (!buf[i - 1]) --i;
-    }
-    return i;
-}
-
 static double
 load_mantissa(double d, const char *buf, long len)
 {
@@ -370,7 +343,6 @@ load_mantissa(double d, const char *buf, long len)
 }
 #else
 #define load_mantissa(d, buf, len) (d)
-#define save_mantissa(d, buf) 0
 #endif
 
 #ifdef DBL_DIG
@@ -382,29 +354,23 @@ load_mantissa(double d, const char *buf, long len)
 static void
 w_float(double d, struct dump_arg *arg)
 {
+    int ruby_dbl2cstr(double value, char *buf, int size);
     char buf[FLOAT_DIG + (DECIMAL_MANT + 7) / 8 + 10];
 
     if (isinf(d)) {
-	if (d < 0) strcpy(buf, "-inf");
-	else       strcpy(buf, "inf");
+	if (d < 0) w_cstr("-inf", arg);
+	else       w_cstr("inf", arg);
     }
     else if (isnan(d)) {
-	strcpy(buf, "nan");
+	w_cstr("nan", arg);
     }
     else if (d == 0.0) {
-	if (1.0/d < 0) strcpy(buf, "-0");
-	else           strcpy(buf, "0");
+	if (1.0/d < 0) w_cstr("-0", arg);
+	else           w_cstr("0", arg);
     }
     else {
-	size_t len;
-
-	/* xxx: should not use system's sprintf(3) */
-	snprintf(buf, sizeof(buf), "%.*g", FLOAT_DIG, d);
-	len = strlen(buf);
-	w_bytes(buf, len + save_mantissa(d, buf + len), arg);
-	return;
+	w_bytes(buf, ruby_dbl2cstr(d, buf, (int)sizeof(buf)), arg);
     }
-    w_bytes(buf, strlen(buf), arg);
 }
 
 static void
diff --git a/numeric.c b/numeric.c
index 00d670b70f..31b3756d25 100644
--- a/numeric.c
+++ b/numeric.c
@@ -545,6 +545,8 @@ rb_float_new(double d)
     return (VALUE)flt;
 }
 
+int ruby_dbl2cstr(double value, char *buf, int size);
+
 /*
  *  call-seq:
  *     flt.to_s  ->  string
@@ -558,70 +560,70 @@ rb_float_new(double d)
 static VALUE
 flo_to_s(VALUE flt)
 {
-    char *ruby_dtoa(double d_, int mode, int ndigits, int *decpt, int *sign, char **rve);
     enum {decimal_mant = DBL_MANT_DIG-DBL_DIG};
     enum {float_dig = DBL_DIG+1};
     char buf[float_dig + (decimal_mant + CHAR_BIT - 1) / CHAR_BIT + 10];
     double value = RFLOAT_VALUE(flt);
-    VALUE s;
-    char *p, *e;
-    int sign, decpt, digs;
 
     if (isinf(value))
 	return rb_usascii_str_new2(value < 0 ? "-Infinity" : "Infinity");
     else if (isnan(value))
 	return rb_usascii_str_new2("NaN");
+    return rb_usascii_str_new(buf, ruby_dbl2cstr(value, buf, (int)sizeof(buf)));
+}
 
+int
+ruby_dbl2cstr(double value, char *buf, int size)
+{
+    char *ruby_dtoa(double d_, int mode, int ndigits, int *decpt, int *sign, char **rve);
+    char *p, *e;
+    int sign, decpt, digs;
+
+    if (size <= 0) return 0;
     p = ruby_dtoa(value, 0, 0, &decpt, &sign, &e);
-    s = sign ? rb_usascii_str_new_cstr("-") : rb_usascii_str_new(0, 0);
-    if ((digs = (int)(e - p)) >= (int)sizeof(buf)) digs = (int)sizeof(buf) - 1;
-    memcpy(buf, p, digs);
-    xfree(p);
-    if (decpt > 0) {
-	if (decpt < digs) {
-	    memmove(buf + decpt + 1, buf + decpt, digs - decpt);
-	    buf[decpt] = '.';
-	    rb_str_cat(s, buf, digs + 1);
-	}
-	else if (decpt - digs < float_dig) {
-	    long len;
-	    char *ptr;
-	    rb_str_cat(s, buf, digs);
-	    rb_str_resize(s, (len = RSTRING_LEN(s)) + decpt - digs + 2);
-	    ptr = RSTRING_PTR(s) + len;
-	    if (decpt > digs) {
-		memset(ptr, '0', decpt - digs);
-		ptr += decpt - digs;
+    if (sign) *buf++ = '-', --size;
+    if ((digs = (int)(e - p)) >= size) digs = size - 1;
+    if (decpt > -4 && (decpt < digs || decpt - digs < DBL_DIG+1)) {
+	int i = 0, j = 0, n;
+	if (decpt > 0) {
+	    memcpy(buf + j, p + i, (n = decpt > digs ? digs : decpt));
+	    i += n, j += n;
+	    if ((n = decpt - n) > 0) {
+		memset(buf + j, '0', n);
+		j += n;
 	    }
-	    memcpy(ptr, ".0", 2);
 	}
 	else {
-	    goto exp;
+	    buf[j++] = '0';
 	}
-    }
-    else if (decpt > -4) {
-	long len;
-	char *ptr;
-	rb_str_cat(s, "0.", 2);
-	rb_str_resize(s, (len = RSTRING_LEN(s)) - decpt + digs);
-	ptr = RSTRING_PTR(s);
-	memset(ptr += len, '0', -decpt);
-	memcpy(ptr -= decpt, buf, digs);
+	buf[j++] = '.';
+	if (decpt < 0) {
+	    memset(buf + j, '0', -decpt);
+	    j -= decpt, decpt = 0;
+	}
+	if (decpt < digs) {
+	    memcpy(buf + j, p + i, (n = digs - decpt));
+	    j += n;
+	}
+	else {
+	    buf[j++] = '0';
+	}
+	digs = j;
     }
     else {
-      exp:
+	buf[0] = p[0];
+	buf[1] = '.';
 	if (digs > 1) {
-	    memmove(buf + 2, buf + 1, digs - 1);
+	    memcpy(buf + 2, p + 1, digs++ - 1);
 	}
 	else {
 	    buf[2] = '0';
-	    digs++;
+	    digs = 3;
 	}
-	buf[1] = '.';
-	rb_str_cat(s, buf, digs + 1);
-	rb_str_catf(s, "e%+03d", decpt - 1);
+	digs += snprintf(buf + digs, size - digs, "e%+03d", decpt - 1);
     }
-    return s;
+    xfree(p);
+    return digs + sign;
 }
 
 /*