correctly rounded floating-point conversions

in new package strconv.

move atoi etc to strconv too.

update fmt, etc to use strconv.

R=r
DELTA=2232  (1691 added, 424 deleted, 117 changed)
OCL=19286
CL=19380

src/lib/strconv/testatof.go

@@ -0,0 +1,46 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "strconv"
+
+type Test struct {
+	in string;
+	out string;
+}
+
+var tests = []Test {
+	Test{ "1", "1" },
+	Test{ "1e23", "1e+23" },
+	Test{ "100000000000000000000000", "1e+23" },
+	Test{ "1e-100", "1e-100" },
+	Test{ "123456700", "1.234567e+08" },
+	Test{ "99999999999999974834176", "9.999999999999997e+22" },
+	Test{ "100000000000000000000001", "1.0000000000000001e+23" },
+	Test{ "100000000000000008388608", "1.0000000000000001e+23" },
+	Test{ "100000000000000016777215", "1.0000000000000001e+23" },
+	Test{ "100000000000000016777216", "1.0000000000000003e+23" },
+	Test{ "-1", "-1" },
+	Test{ "-0", "0" },
+}
+
+func main() {
+	bad := 0;
+	for i := 0; i < len(tests); i++ {
+		t := &tests[i];
+		f, overflow, ok := strconv.atof64(t.in);
+		if !ok {
+			panicln("test", t.in);
+		}
+		s := strconv.ftoa64(f, 'g', -1);
+		if s != t.out {
+			println("test", t.in, "want", t.out, "got", s);
+			bad++;
+		}
+	}
+	if bad != 0 {
+		panic("failed");
+	}
+}