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Commit 2df1ccdb authored by Robert Griesemer's avatar Robert Griesemer
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math/big: Always print exponent sign when using 'p' exponent for Floats. 

Float.Format supports the 'b' and 'p' format, both of which print
a binary ('p') exponent. The 'b' format always printed a sign ('+'
or '-') for the exponent; the 'p' format only printed a negative
sign for the exponent. This change makes the two consistent. It
also makes the 'p' format easier to read if the exponent is >= 0.

Also:
- Comments added elsewhere.

Change-Id: Ifd2e01bdafb3043345972ca22a90248d055bd29b
Reviewed-on: https://go-review.googlesource.com/10359Reviewed-by: default avatarAlan Donovan <adonovan@google.com>
parent 22e4b816
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Showing with 48 additions and 40 deletions
src/math/big/bits_test.go
View file @ 2df1ccdb
......@@ -203,18 +203,18 @@ func TestFromBits(t *testing.T) {
}{
// all different bit numbers
{nil, "0"},
{Bits{0}, "0x.8p1"},
{Bits{1}, "0x.8p2"},
{Bits{-1}, "0x.8p0"},
{Bits{63}, "0x.8p64"},
{Bits{33, -30}, "0x.8000000000000001p34"},
{Bits{255, 0}, "0x.8000000000000000000000000000000000000000000000000000000000000001p256"},
{Bits{0}, "0x.8p+1"},
{Bits{1}, "0x.8p+2"},
{Bits{-1}, "0x.8p+0"},
{Bits{63}, "0x.8p+64"},
{Bits{33, -30}, "0x.8000000000000001p+34"},
{Bits{255, 0}, "0x.8000000000000000000000000000000000000000000000000000000000000001p+256"},
// multiple equal bit numbers
{Bits{0, 0}, "0x.8p2"},
{Bits{0, 0, 0, 0}, "0x.8p3"},
{Bits{0, 1, 0}, "0x.8p3"},
{append(Bits{2, 1, 0} /* 7 */, Bits{3, 1} /* 10 */ ...), "0x.88p5" /* 17 */},
{Bits{0, 0}, "0x.8p+2"},
{Bits{0, 0, 0, 0}, "0x.8p+3"},
{Bits{0, 1, 0}, "0x.8p+3"},
{append(Bits{2, 1, 0} /* 7 */, Bits{3, 1} /* 10 */ ...), "0x.88p+5" /* 17 */},
} {
f := test.bits.Float()
if got := f.Format('p', 0); got != test.want {
......
src/math/big/float.go
View file @ 2df1ccdb
......@@ -913,6 +913,7 @@ func (x *Float) Float32() (float32, Accuracy) {
}
return float32(math.Inf(+1)), Above
}
// e <= emax
// Determine sign, biased exponent, and mantissa.
var sign, bexp, mant uint32
......@@ -1019,6 +1020,7 @@ func (x *Float) Float64() (float64, Accuracy) {
}
return math.Inf(+1), Above
}
// e <= emax
// Determine sign, biased exponent, and mantissa.
var sign, bexp, mant uint64
......
src/math/big/float_test.go
View file @ 2df1ccdb
......@@ -1564,31 +1564,31 @@ func TestFloatArithmeticOverflow(t *testing.T) {
acc Accuracy
}{
{4, ToNearestEven, '+', "0", "0", "0", Exact}, // smoke test
{4, ToNearestEven, '+', "0x.8p0", "0x.8p0", "0x.8p1", Exact}, // smoke test
{4, ToNearestEven, '+', "0x.8p+0", "0x.8p+0", "0x.8p+1", Exact}, // smoke test
{4, ToNearestEven, '+', "0", "0x.8p2147483647", "0x.8p2147483647", Exact},
{4, ToNearestEven, '+', "0x.8p2147483500", "0x.8p2147483647", "0x.8p2147483647", Below}, // rounded to zero
{4, ToNearestEven, '+', "0", "0x.8p2147483647", "0x.8p+2147483647", Exact},
{4, ToNearestEven, '+', "0x.8p2147483500", "0x.8p2147483647", "0x.8p+2147483647", Below}, // rounded to zero
{4, ToNearestEven, '+', "0x.8p2147483647", "0x.8p2147483647", "+Inf", Above}, // exponent overflow in +
{4, ToNearestEven, '+', "-0x.8p2147483647", "-0x.8p2147483647", "-Inf", Below}, // exponent overflow in +
{4, ToNearestEven, '-', "-0x.8p2147483647", "0x.8p2147483647", "-Inf", Below}, // exponent overflow in -
{4, ToZero, '+', "0x.fp2147483647", "0x.8p2147483643", "0x.fp2147483647", Below}, // rounded to zero
{4, ToZero, '+', "0x.fp2147483647", "0x.8p2147483643", "0x.fp+2147483647", Below}, // rounded to zero
{4, ToNearestEven, '+', "0x.fp2147483647", "0x.8p2147483643", "+Inf", Above}, // exponent overflow in rounding
{4, AwayFromZero, '+', "0x.fp2147483647", "0x.8p2147483643", "+Inf", Above}, // exponent overflow in rounding
{4, AwayFromZero, '-', "-0x.fp2147483647", "0x.8p2147483644", "-Inf", Below}, // exponent overflow in rounding
{4, ToNearestEven, '-', "-0x.fp2147483647", "0x.8p2147483643", "-Inf", Below}, // exponent overflow in rounding
{4, ToZero, '-', "-0x.fp2147483647", "0x.8p2147483643", "-0x.fp2147483647", Above}, // rounded to zero
{4, ToZero, '-', "-0x.fp2147483647", "0x.8p2147483643", "-0x.fp+2147483647", Above}, // rounded to zero
{4, ToNearestEven, '+', "0", "0x.8p-2147483648", "0x.8p-2147483648", Exact},
{4, ToNearestEven, '+', "0x.8p-2147483648", "0x.8p-2147483648", "0x.8p-2147483647", Exact},
{4, ToNearestEven, '*', "1", "0x.8p2147483647", "0x.8p2147483647", Exact},
{4, ToNearestEven, '*', "1", "0x.8p2147483647", "0x.8p+2147483647", Exact},
{4, ToNearestEven, '*', "2", "0x.8p2147483647", "+Inf", Above}, // exponent overflow in *
{4, ToNearestEven, '*', "-2", "0x.8p2147483647", "-Inf", Below}, // exponent overflow in *
{4, ToNearestEven, '/', "0.5", "0x.8p2147483647", "0x.8p-2147483646", Exact},
{4, ToNearestEven, '/', "0x.8p0", "0x.8p2147483647", "0x.8p-2147483646", Exact},
{4, ToNearestEven, '/', "0x.8p+0", "0x.8p2147483647", "0x.8p-2147483646", Exact},
{4, ToNearestEven, '/', "0x.8p-1", "0x.8p2147483647", "0x.8p-2147483647", Exact},
{4, ToNearestEven, '/', "0x.8p-2", "0x.8p2147483647", "0x.8p-2147483648", Exact},
{4, ToNearestEven, '/', "0x.8p-3", "0x.8p2147483647", "0", Below}, // exponent underflow in /
......
src/math/big/floatconv.go
View file @ 2df1ccdb
......@@ -67,6 +67,7 @@ func (z *Float) SetString(s string) (*Float, bool) {
// defined if an error is reported.
//
// BUG(gri) The Float.Scan signature conflicts with Scan(s fmt.ScanState, ch rune) error.
// (https://github.com/golang/go/issues/10938)
func (z *Float) Scan(r io.ByteScanner, base int) (f *Float, b int, err error) {
prec := z.prec
if prec == 0 {
......@@ -268,6 +269,8 @@ func ParseFloat(s string, base int, prec uint, mode RoundingMode) (f *Float, b i
// The prec value is ignored for the 'b' or 'p' format.
//
// BUG(gri) Float.Format does not accept negative precisions.
// BUG(gri) The Float.Format signature conflicts with Format(f fmt.State, c rune).
// (https://github.com/golang/go/issues/10938)
func (x *Float) Format(format byte, prec int) string {
const extra = 10 // TODO(gri) determine a good/better value here
return string(x.Append(make([]byte, 0, prec+extra), format, prec))
......@@ -369,5 +372,8 @@ func (x *Float) pstring(buf []byte) []byte {
buf = append(buf, "0x."...)
buf = append(buf, strings.TrimRight(x.mant.hexString(), "0")...)
buf = append(buf, 'p')
if x.exp >= 0 {
buf = append(buf, '+')
}
return strconv.AppendInt(buf, int64(x.exp), 10)
}
src/math/big/floatconv_test.go
View file @ 2df1ccdb
......@@ -145,8 +145,8 @@ func TestFloat64Format(t *testing.T) {
{0, 'p', 0, "0"},
{math.Copysign(0, -1), 'p', 0, "-0"},
{1024.0, 'p', 0, "0x.8p11"},
{-1024.0, 'p', 0, "-0x.8p11"},
{1024.0, 'p', 0, "0x.8p+11"},
{-1024.0, 'p', 0, "-0x.8p+11"},
// all test cases below from strconv/ftoa_test.go
{1, 'e', 5, "1.00000e+00"},
......@@ -331,8 +331,8 @@ func TestFloatFormat(t *testing.T) {
{"3e40", 100, 'g', 40, "3e+40"},
// make sure "stupid" exponents don't stall the machine
{"1e1000000", 64, 'p', 0, "0x.88b3a28a05eade3ap3321929"},
{"1e1000000000", 64, 'p', 0, "0x.ecc5f45aa573d3p1538481529"},
{"1e1000000", 64, 'p', 0, "0x.88b3a28a05eade3ap+3321929"},
{"1e1000000000", 64, 'p', 0, "0x.ecc5f45aa573d3p+1538481529"},
{"1e-1000000", 64, 'p', 0, "0x.efb4542cc8ca418ap-3321928"},
{"1e-1000000000", 64, 'p', 0, "0x.8a64dd983a4c7dabp-1538481528"},
......@@ -352,17 +352,17 @@ func TestFloatFormat(t *testing.T) {
{"3.00", 350, 'b', 0, "1720123961992553633708115671476565205597423741876210842803191629540192157066363606052513914832594264915968p-348"},
{"3.000", 350, 'b', 0, "1720123961992553633708115671476565205597423741876210842803191629540192157066363606052513914832594264915968p-348"},
{"3", 350, 'p', 0, "0x.cp2"},
{"03", 350, 'p', 0, "0x.cp2"},
{"3.", 350, 'p', 0, "0x.cp2"},
{"3.0", 350, 'p', 0, "0x.cp2"},
{"3.00", 350, 'p', 0, "0x.cp2"},
{"3.000", 350, 'p', 0, "0x.cp2"},
{"3", 350, 'p', 0, "0x.cp+2"},
{"03", 350, 'p', 0, "0x.cp+2"},
{"3.", 350, 'p', 0, "0x.cp+2"},
{"3.0", 350, 'p', 0, "0x.cp+2"},
{"3.00", 350, 'p', 0, "0x.cp+2"},
{"3.000", 350, 'p', 0, "0x.cp+2"},
{"0", 64, 'p', 0, "0"},
{"-0", 64, 'p', 0, "-0"},
{"1024.0", 64, 'p', 0, "0x.8p11"},
{"-1024.0", 64, 'p', 0, "-0x.8p11"},
{"1024.0", 64, 'p', 0, "0x.8p+11"},
{"-1024.0", 64, 'p', 0, "-0x.8p+11"},
// unsupported format
{"3.14", 64, 'x', 0, "%x"},
......
src/math/big/floatexample_test.go
View file @ 2df1ccdb
......@@ -21,9 +21,9 @@ func ExampleFloat_Add() {
fmt.Printf("y = %s (%s, prec = %d, acc = %s)\n", &y, y.Format('p', 0), y.Prec(), y.Acc())
fmt.Printf("z = %s (%s, prec = %d, acc = %s)\n", &z, z.Format('p', 0), z.Prec(), z.Acc())
// Output:
// x = 1000 (0x.fap10, prec = 64, acc = Exact)
// y = 2.718281828 (0x.adf85458248cd8p2, prec = 53, acc = Exact)
// z = 1002.718282 (0x.faadf854p10, prec = 32, acc = Below)
// x = 1000 (0x.fap+10, prec = 64, acc = Exact)
// y = 2.718281828 (0x.adf85458248cd8p+2, prec = 53, acc = Exact)
// z = 1002.718282 (0x.faadf854p+10, prec = 32, acc = Below)
}
func Example_Shift() {
......
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