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time: correctly parse large input durations and avoid precision loss

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Do not lose precision for durations specified without fractions
that can be represented by an int64 such as 1<<53+1 nanoseconds.
Previously there was some precision lost in floating point conversion.

Handle overflow for durations above 1<<63-1 nanoseconds but not earlier.

Add tests to cover the above cases.

Change-Id: I4bcda93cee1673e501ecb6a9eef3914ee29aecd2
Reviewed-on: https://go-review.googlesource.com/2461
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Martin Möhrmann 2015-01-07 19:56:06 +01:00 committed by Robert Griesemer
parent 3b63b69d2f
commit d1210acffd
2 changed files with 66 additions and 28 deletions
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71
src/time/format.go
View File

@ -1131,24 +1131,28 @@ func leadingInt(s string) (x int64, rem string, err error) {
if c < '0' || c > '9' {
break
}
if x >= (1<<63-10)/10 {
if x > (1<<63-1)/10 {
// overflow
return 0, "", errLeadingInt
}
x = x*10 + int64(c) - '0'
if x < 0 {
// overflow
return 0, "", errLeadingInt
}
}
return x, s[i:], nil
}
var unitMap = map[string]float64{
"ns": float64(Nanosecond),
"us": float64(Microsecond),
"µs": float64(Microsecond), // U+00B5 = micro symbol
"μs": float64(Microsecond), // U+03BC = Greek letter mu
"ms": float64(Millisecond),
"s": float64(Second),
"m": float64(Minute),
"h": float64(Hour),
var unitMap = map[string]int64{
"ns": int64(Nanosecond),
"us": int64(Microsecond),
"µs": int64(Microsecond), // U+00B5 = micro symbol
"μs": int64(Microsecond), // U+03BC = Greek letter mu
"ms": int64(Millisecond),
"s": int64(Second),
"m": int64(Minute),
"h": int64(Hour),
}
// ParseDuration parses a duration string.
@ -1159,7 +1163,7 @@ var unitMap = map[string]float64{
func ParseDuration(s string) (Duration, error) {
// [-+]?([0-9]*(\.[0-9]*)?[a-z]+)+
orig := s
f := float64(0)
var d int64
neg := false
// Consume [-+]?
@ -1178,22 +1182,23 @@ func ParseDuration(s string) (Duration, error) {
return 0, errors.New("time: invalid duration " + orig)
}
for s != "" {
g := float64(0) // this element of the sequence
var (
v, f int64 // integers before, after decimal point
scale float64 = 1 // value = v + f/scale
)
var x int64
var err error
// The next character must be [0-9.]
if !(s[0] == '.' || ('0' <= s[0] && s[0] <= '9')) {
if !(s[0] == '.' || '0' <= s[0] && s[0] <= '9') {
return 0, errors.New("time: invalid duration " + orig)
}
// Consume [0-9]*
pl := len(s)
x, s, err = leadingInt(s)
v, s, err = leadingInt(s)
if err != nil {
return 0, errors.New("time: invalid duration " + orig)
}
g = float64(x)
pre := pl != len(s) // whether we consumed anything before a period
// Consume (\.[0-9]*)?
@ -1201,15 +1206,13 @@ func ParseDuration(s string) (Duration, error) {
if s != "" && s[0] == '.' {
s = s[1:]
pl := len(s)
x, s, err = leadingInt(s)
f, s, err = leadingInt(s)
if err != nil {
return 0, errors.New("time: invalid duration " + orig)
}
scale := 1.0
for n := pl - len(s); n > 0; n-- {
scale *= 10
}
g += float64(x) / scale
post = pl != len(s)
}
if !pre && !post {
@ -1221,7 +1224,7 @@ func ParseDuration(s string) (Duration, error) {
i := 0
for ; i < len(s); i++ {
c := s[i]
if c == '.' || ('0' <= c && c <= '9') {
if c == '.' || '0' <= c && c <= '9' {
break
}
}
@ -1234,15 +1237,29 @@ func ParseDuration(s string) (Duration, error) {
if !ok {
return 0, errors.New("time: unknown unit " + u + " in duration " + orig)
}
f += g * unit
if v > (1<<63-1)/unit {
// overflow
return 0, errors.New("time: invalid duration " + orig)
}
v *= unit
if f > 0 {
// float64 is needed to be nanosecond accurate for fractions of hours.
// v >= 0 && (f*unit/scale) <= 3.6e+12 (ns/h, h is the largest unit)
v += int64(float64(f) * (float64(unit) / scale))
if v < 0 {
// overflow
return 0, errors.New("time: invalid duration " + orig)
}
}
d += v
if d < 0 {
// overflow
return 0, errors.New("time: invalid duration " + orig)
}
}
if neg {
f = -f
d = -d
}
if f < float64(-1<<63) || f > float64(1<<63-1) {
return 0, errors.New("time: overflow parsing duration")
}
return Duration(f), nil
return Duration(d), nil
}

23
src/time/time_test.go
View File

@ -832,6 +832,14 @@ var parseDurationTests = []struct {
{"52763797000ns", true, 52763797000 * Nanosecond},
// more than 9 digits after decimal point, see http://golang.org/issue/6617
{"0.3333333333333333333h", true, 20 * Minute},
// 9007199254740993 = 1<<53+1 cannot be stored precisely in a float64
{"9007199254740993ns", true, (1<<53 + 1) * Nanosecond},
// largest duration that can be represented by int64 in nanoseconds
{"9223372036854775807ns", true, (1<<63 - 1) * Nanosecond},
{"9223372036854775.807us", true, (1<<63 - 1) * Nanosecond},
{"9223372036s854ms775us807ns", true, (1<<63 - 1) * Nanosecond},
// large negative value
{"-9223372036854775807ns", true, -1<<63 + 1*Nanosecond},
// errors
{"", false, 0},
@ -842,7 +850,13 @@ var parseDurationTests = []struct {
{"-.", false, 0},
{".s", false, 0},
{"+.s", false, 0},
{"3000000h", false, 0}, // overflow
{"3000000h", false, 0}, // overflow
{"9223372036854775808ns", false, 0}, // overflow
{"9223372036854775.808us", false, 0}, // overflow
{"9223372036854ms775us808ns", false, 0}, // overflow
// largest negative value of type int64 in nanoseconds should fail
// see https://go-review.googlesource.com/#/c/2461/
{"-9223372036854775808ns", false, 0},
}
func TestParseDuration(t *testing.T) {
@ -1052,6 +1066,13 @@ func BenchmarkParse(b *testing.B) {
}
}
func BenchmarkParseDuration(b *testing.B) {
for i := 0; i < b.N; i++ {
ParseDuration("9007199254.740993ms")
ParseDuration("9007199254740993ns")
}
}
func BenchmarkHour(b *testing.B) {
t := Now()
for i := 0; i < b.N; i++ {