diff --git a/jsdtoa.c b/jsdtoa.c
new file mode 100644
index 0000000..3910fe8
--- /dev/null
+++ b/jsdtoa.c
@@ -0,0 +1,329 @@
+/* The authors of this software are Rob Pike and Ken Thompson.
+ * Copyright (c) 2002 by Lucent Technologies.
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose without fee is hereby granted, provided that this entire notice
+ * is included in all copies of any software which is or includes a copy
+ * or modification of this software and in all copies of the supporting
+ * documentation for such software.
+ * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTY. IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES MAKE ANY
+ * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
+ * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
+ */
+
+#include <stdio.h>
+#include <math.h>
+#include <float.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+
+enum { NSIGNIF	= 17 };
+
+/*
+ * first few powers of 10, enough for about 1/2 of the
+ * total space for doubles.
+ */
+static double pows10[] =
+{
+	1e0,	1e1,	1e2,	1e3,	1e4,	1e5,	1e6,	1e7,	1e8,	1e9,
+	1e10,	1e11,	1e12,	1e13,	1e14,	1e15,	1e16,	1e17,	1e18,	1e19,
+	1e20,	1e21,	1e22,	1e23,	1e24,	1e25,	1e26,	1e27,	1e28,	1e29,
+	1e30,	1e31,	1e32,	1e33,	1e34,	1e35,	1e36,	1e37,	1e38,	1e39,
+	1e40,	1e41,	1e42,	1e43,	1e44,	1e45,	1e46,	1e47,	1e48,	1e49,
+	1e50,	1e51,	1e52,	1e53,	1e54,	1e55,	1e56,	1e57,	1e58,	1e59,
+	1e60,	1e61,	1e62,	1e63,	1e64,	1e65,	1e66,	1e67,	1e68,	1e69,
+	1e70,	1e71,	1e72,	1e73,	1e74,	1e75,	1e76,	1e77,	1e78,	1e79,
+	1e80,	1e81,	1e82,	1e83,	1e84,	1e85,	1e86,	1e87,	1e88,	1e89,
+	1e90,	1e91,	1e92,	1e93,	1e94,	1e95,	1e96,	1e97,	1e98,	1e99,
+	1e100,	1e101,	1e102,	1e103,	1e104,	1e105,	1e106,	1e107,	1e108,	1e109,
+	1e110,	1e111,	1e112,	1e113,	1e114,	1e115,	1e116,	1e117,	1e118,	1e119,
+	1e120,	1e121,	1e122,	1e123,	1e124,	1e125,	1e126,	1e127,	1e128,	1e129,
+	1e130,	1e131,	1e132,	1e133,	1e134,	1e135,	1e136,	1e137,	1e138,	1e139,
+	1e140,	1e141,	1e142,	1e143,	1e144,	1e145,	1e146,	1e147,	1e148,	1e149,
+	1e150,	1e151,	1e152,	1e153,	1e154,	1e155,	1e156,	1e157,	1e158,	1e159,
+};
+#define	npows10 ((int)(sizeof(pows10)/sizeof(pows10[0])))
+#define	pow10(x)  fmtpow10(x)
+
+static double
+pow10(int n)
+{
+	double d;
+	int neg;
+
+	neg = 0;
+	if(n < 0){
+		neg = 1;
+		n = -n;
+	}
+
+	if(n < npows10)
+		d = pows10[n];
+	else{
+		d = pows10[npows10-1];
+		for(;;){
+			n -= npows10 - 1;
+			if(n < npows10){
+				d *= pows10[n];
+				break;
+			}
+			d *= pows10[npows10 - 1];
+		}
+	}
+	if(neg)
+		return 1./d;
+	return d;
+}
+
+/*
+ * add 1 to the decimal integer string a of length n.
+ * if 99999 overflows into 10000, return 1 to tell caller
+ * to move the virtual decimal point.
+ */
+static int
+xadd1(char *a, int n)
+{
+	char *b;
+	int c;
+
+	if(n < 0 || n > NSIGNIF)
+		return 0;
+	for(b = a+n-1; b >= a; b--) {
+		c = *b + 1;
+		if(c <= '9') {
+			*b = c;
+			return 0;
+		}
+		*b = '0';
+	}
+	/*
+	 * need to overflow adding digit.
+	 * shift number down and insert 1 at beginning.
+	 * decimal is known to be 0s or we wouldn't
+	 * have gotten this far.  (e.g., 99999+1 => 00000)
+	 */
+	a[0] = '1';
+	return 1;
+}
+
+/*
+ * subtract 1 from the decimal integer string a.
+ * if 10000 underflows into 09999, make it 99999
+ * and return 1 to tell caller to move the virtual
+ * decimal point.  this way, xsub1 is inverse of xadd1.
+ */
+static int
+xsub1(char *a, int n)
+{
+	char *b;
+	int c;
+
+	if(n < 0 || n > NSIGNIF)
+		return 0;
+	for(b = a+n-1; b >= a; b--) {
+		c = *b - 1;
+		if(c >= '0') {
+			if(c == '0' && b == a) {
+				/*
+				 * just zeroed the top digit; shift everyone up.
+				 * decimal is known to be 9s or we wouldn't
+				 * have gotten this far.  (e.g., 10000-1 => 09999)
+				 */
+				*b = '9';
+				return 1;
+			}
+			*b = c;
+			return 0;
+		}
+		*b = '9';
+	}
+	/*
+	 * can't get here.  the number a is always normalized
+	 * so that it has a nonzero first digit.
+	 */
+	abort();
+}
+
+/*
+ * format exponent like sprintf(p, "e%+d", e)
+ */
+void
+jsV_fmtexp(char *p, int e)
+{
+	char se[9];
+	int i;
+
+	*p++ = 'e';
+	if(e < 0) {
+		*p++ = '-';
+		e = -e;
+	} else
+		*p++ = '+';
+	i = 0;
+	while(e) {
+		se[i++] = e % 10 + '0';
+		e /= 10;
+	}
+	while(i < 1)
+		se[i++] = '0';
+	while(i > 0)
+		*p++ = se[--i];
+	*p++ = '\0';
+}
+
+/*
+ * compute decimal integer m, exp such that:
+ *	f = m*10^exp
+ *	m is as short as possible with losing exactness
+ * assumes special cases (NaN, +Inf, -Inf) have been handled.
+ */
+void
+jsV_dtoa(double f, char *s, int *exp, int *neg, int *ns)
+{
+	int c, d, e2, e, ee, i, ndigit, oerrno;
+	char tmp[NSIGNIF+10];
+	double g;
+
+	oerrno = errno; /* in case strtod smashes errno */
+
+	/*
+	 * make f non-negative.
+	 */
+	*neg = 0;
+	if(f < 0) {
+		f = -f;
+		*neg = 1;
+	}
+
+	/*
+	 * must handle zero specially.
+	 */
+	if(f == 0){
+		*exp = 0;
+		s[0] = '0';
+		s[1] = '\0';
+		*ns = 1;
+		return;
+	}
+
+	/*
+	 * find g,e such that f = g*10^e.
+	 * guess 10-exponent using 2-exponent, then fine tune.
+	 */
+	frexp(f, &e2);
+	e = (int)(e2 * .301029995664);
+	g = f * pow10(-e);
+	while(g < 1) {
+		e--;
+		g = f * pow10(-e);
+	}
+	while(g >= 10) {
+		e++;
+		g = f * pow10(-e);
+	}
+
+	/*
+	 * convert NSIGNIF digits as a first approximation.
+	 */
+	for(i=0; i<NSIGNIF; i++) {
+		d = (int)g;
+		s[i] = d+'0';
+		g = (g-d) * 10;
+	}
+	s[i] = 0;
+
+	/*
+	 * adjust e because s is 314159... not 3.14159...
+	 */
+	e -= NSIGNIF-1;
+	jsV_fmtexp(s+NSIGNIF, e);
+
+	/*
+	 * adjust conversion until strtod(s) == f exactly.
+	 */
+	for(i=0; i<10; i++) {
+		g = strtod(s, NULL);
+		if(f > g) {
+			if(xadd1(s, NSIGNIF)) {
+				/* gained a digit */
+				e--;
+				jsV_fmtexp(s+NSIGNIF, e);
+			}
+			continue;
+		}
+		if(f < g) {
+			if(xsub1(s, NSIGNIF)) {
+				/* lost a digit */
+				e++;
+				jsV_fmtexp(s+NSIGNIF, e);
+			}
+			continue;
+		}
+		break;
+	}
+
+	/*
+	 * play with the decimal to try to simplify.
+	 */
+
+	/*
+	 * bump last few digits up to 9 if we can
+	 */
+	for(i=NSIGNIF-1; i>=NSIGNIF-3; i--) {
+		c = s[i];
+		if(c != '9') {
+			s[i] = '9';
+			g = strtod(s, NULL);
+			if(g != f) {
+				s[i] = c;
+				break;
+			}
+		}
+	}
+
+	/*
+	 * add 1 in hopes of turning 9s to 0s
+	 */
+	if(s[NSIGNIF-1] == '9') {
+		strcpy(tmp, s);
+		ee = e;
+		if(xadd1(tmp, NSIGNIF)) {
+			ee--;
+			jsV_fmtexp(tmp+NSIGNIF, ee);
+		}
+		g = strtod(tmp, NULL);
+		if(g == f) {
+			strcpy(s, tmp);
+			e = ee;
+		}
+	}
+
+	/*
+	 * bump last few digits down to 0 as we can.
+	 */
+	for(i=NSIGNIF-1; i>=NSIGNIF-3; i--) {
+		c = s[i];
+		if(c != '0') {
+			s[i] = '0';
+			g = strtod(s, NULL);
+			if(g != f) {
+				s[i] = c;
+				break;
+			}
+		}
+	}
+
+	/*
+	 * remove trailing zeros.
+	 */
+	ndigit = NSIGNIF;
+	while(ndigit > 1 && s[ndigit-1] == '0'){
+		e++;
+		--ndigit;
+	}
+	s[ndigit] = 0;
+	*exp = e;
+	*ns = ndigit;
+	errno = oerrno;
+}
diff --git a/jsnumber.c b/jsnumber.c
index aa5fd3c..d4f9e2c 100644
--- a/jsnumber.c
+++ b/jsnumber.c
@@ -34,12 +34,19 @@ static void Np_toString(js_State *J)
 /* Customized ToString() on a number */
 void numtostr(js_State *J, const char *fmt, int w, double n)
 {
-	char buf[40];
+	char buf[32], *e;
 	if (isnan(n)) js_pushliteral(J, "NaN");
 	else if (isinf(n)) js_pushliteral(J, n < 0 ? "-Infinity" : "Infinity");
 	else if (n == 0) js_pushliteral(J, "0");
 	else {
+		if (w < 1) w = 1;
+		if (w > 17) w = 17;
 		sprintf(buf, fmt, w, n);
+		e = strchr(buf, 'e');
+		if (e) {
+			int exp = atoi(e+1);
+			sprintf(e, "e%+d", exp);
+		}
 		js_pushstring(J, buf);
 	}
 }
diff --git a/jsvalue.c b/jsvalue.c
index 3f8daa2..fe79cf4 100644
--- a/jsvalue.c
+++ b/jsvalue.c
@@ -104,6 +104,7 @@ js_Value jsV_toprimitive(js_State *J, const js_Value *v, int preferred)
 			return vv;
 		}
 	}
+
 	js_typeerror(J, "cannot convert object to primitive");
 }
 
@@ -187,13 +188,53 @@ double jsV_tointeger(js_State *J, const js_Value *v)
 }
 
 /* ToString() on a number */
-const char *jsV_numbertostring(js_State *J, double n)
+const char *jsV_numbertostring(js_State *J, double f)
 {
-	char buf[32];
-	if (isnan(n)) return "NaN";
-	if (isinf(n)) return n < 0 ? "-Infinity" : "Infinity";
-	if (n == 0) return "0";
-	sprintf(buf, "%.17g", n); /* DBL_DECIMAL_DIG == 17 */
+	char buf[32], digits[32], *p = buf, *s = digits;
+	int exp, neg, ndigits, point;
+
+	if (isnan(f)) return "NaN";
+	if (isinf(f)) return f < 0 ? "-Infinity" : "Infinity";
+	if (f == 0) return "0";
+
+	jsV_dtoa(f, digits, &exp, &neg, &ndigits);
+	point = ndigits + exp;
+
+	if (neg)
+		*p++ = '-';
+
+	if (point < -5 || point > 21) {
+		*p++ = *s++;
+		if (ndigits > 1) {
+			int n = ndigits - 1;
+			*p++ = '.';
+			while (n--)
+				*p++ = *s++;
+		}
+		jsV_fmtexp(p, point - 1);
+	}
+
+	else if (point <= 0) {
+		*p++ = '0';
+		*p++ = '.';
+		while (point++ < 0)
+			*p++ = '0';
+		while (ndigits-- > 0)
+			*p++ = *s++;
+		*p = 0;
+	}
+
+	else {
+		while (ndigits-- > 0) {
+			*p++ = *s++;
+			if (--point == 0 && ndigits > 0)
+				*p++ = '.';
+		}
+		while (point-- > 0)
+			*p++ = '0';
+		*p = 0;
+	}
+
 	return js_intern(J, buf);
 }
 
diff --git a/jsvalue.h b/jsvalue.h
index d927d48..c6dbe15 100644
--- a/jsvalue.h
+++ b/jsvalue.h
@@ -132,6 +132,10 @@ unsigned short jsV_numbertouint16(double n);
 const char *jsV_numbertostring(js_State *J, double number);
 double jsV_stringtonumber(js_State *J, const char *string);
 
+/* jsdtoa.c */
+void jsV_fmtexp(char *p, int e);
+void jsV_dtoa(double f, char *digits, int *exp, int *neg, int *ndigits);
+
 /* jsproperty.c */
 js_Object *jsV_newobject(js_State *J, enum js_Class type, js_Object *prototype);
 js_Property *jsV_getownproperty(js_State *J, js_Object *obj, const char *name);
diff --git a/one.c b/one.c
index 0baed89..2193194 100644
--- a/one.c
+++ b/one.c
@@ -3,6 +3,7 @@
 #include "jsbuiltin.c"
 #include "jscompile.c"
 #include "jsdate.c"
+#include "jsdtoa.c"
 #include "jsdump.c"
 #include "jserror.c"
 #include "jsfunction.c"