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math/big: fix formatting for 'b' format

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Fixes #9939.

Change-Id: I9d60722b648fbc00650115da539a7466c6c86552
Reviewed-on: https://go-review.googlesource.com/5640
Reviewed-by: Alan Donovan <adonovan@google.com>
This commit is contained in:
Robert Griesemer 2015-02-23 13:15:10 -08:00
parent f0bbb5c450
commit ce137592c0
2 changed files with 101 additions and 62 deletions
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27
src/math/big/floatconv.go
View File

@ -171,7 +171,7 @@ func ParseFloat(s string, base int, prec uint, mode RoundingMode) (f *Float, b i
// //
// For the binary exponent formats, the mantissa is printed in normalized form: // For the binary exponent formats, the mantissa is printed in normalized form:
// //
// 'b' decimal integer mantissa using x.Precision() bits, or -0 // 'b' decimal integer mantissa using x.Prec() bits, or -0
// 'p' hexadecimal fraction with 0.5 <= 0.mantissa < 1.0, or -0 // 'p' hexadecimal fraction with 0.5 <= 0.mantissa < 1.0, or -0
// //
// The precision prec controls the number of digits (excluding the exponent) // The precision prec controls the number of digits (excluding the exponent)
@ -221,7 +221,7 @@ func (x *Float) String() string {
// bstring appends the string of x in the format ["-"] mantissa "p" exponent // bstring appends the string of x in the format ["-"] mantissa "p" exponent
// with a decimal mantissa and a binary exponent, or ["-"] "0" if x is zero, // with a decimal mantissa and a binary exponent, or ["-"] "0" if x is zero,
// and returns the extended buffer. // and returns the extended buffer.
// The mantissa is normalized such that is uses x.Precision() bits in binary // The mantissa is normalized such that is uses x.Prec() bits in binary
// representation. // representation.
func (x *Float) bstring(buf []byte) []byte { func (x *Float) bstring(buf []byte) []byte {
if x.neg { if x.neg {
@ -231,12 +231,16 @@ func (x *Float) bstring(buf []byte) []byte {
return append(buf, '0') return append(buf, '0')
} }
// x != 0 // x != 0
// normalize mantissa
// adjust mantissa to use exactly x.prec bits
m := x.mant m := x.mant
t := uint(len(x.mant)*_W) - x.prec // 0 <= t < _W switch w := uint(len(x.mant)) * _W; {
if t > 0 { case w < x.prec:
m = nat(nil).shr(m, t) m = nat(nil).shl(m, x.prec-w)
case w > x.prec:
m = nat(nil).shr(m, w-x.prec)
} }
buf = append(buf, m.decimalString()...) buf = append(buf, m.decimalString()...)
buf = append(buf, 'p') buf = append(buf, 'p')
e := int64(x.exp) - int64(x.prec) e := int64(x.exp) - int64(x.prec)
@ -258,7 +262,16 @@ func (x *Float) pstring(buf []byte) []byte {
return append(buf, '0') return append(buf, '0')
} }
// x != 0 // x != 0
// mantissa is stored in normalized form
// remove trailing 0 words early
// (no need to convert to hex 0's and trim later)
m := x.mant
i := 0
for i < len(m) && m[i] == 0 {
i++
}
m = m[i:]
buf = append(buf, "0x."...) buf = append(buf, "0x."...)
buf = append(buf, strings.TrimRight(x.mant.hexString(), "0")...) buf = append(buf, strings.TrimRight(x.mant.hexString(), "0")...)
buf = append(buf, 'p') buf = append(buf, 'p')

136
src/math/big/floatconv_test.go
View File

@ -240,86 +240,112 @@ func TestFloat64Format(t *testing.T) {
func TestFloatFormat(t *testing.T) { func TestFloatFormat(t *testing.T) {
for _, test := range []struct { for _, test := range []struct {
x string x string
prec uint
format byte format byte
prec int digits int
want string want string
}{ }{
{"0", 'f', 0, "0"}, {"0", 10, 'f', 0, "0"},
{"-0", 'f', 0, "-0"}, {"-0", 10, 'f', 0, "-0"},
{"1", 'f', 0, "1"}, {"1", 10, 'f', 0, "1"},
{"-1", 'f', 0, "-1"}, {"-1", 10, 'f', 0, "-1"},
{"1.459", 'e', 0, "1e+00"}, {"1.459", 100, 'e', 0, "1e+00"},
{"2.459", 'e', 1, "2.5e+00"}, {"2.459", 100, 'e', 1, "2.5e+00"},
{"3.459", 'e', 2, "3.46e+00"}, {"3.459", 100, 'e', 2, "3.46e+00"},
{"4.459", 'e', 3, "4.459e+00"}, {"4.459", 100, 'e', 3, "4.459e+00"},
{"5.459", 'e', 4, "5.4590e+00"}, {"5.459", 100, 'e', 4, "5.4590e+00"},
{"1.459", 'E', 0, "1E+00"}, {"1.459", 100, 'E', 0, "1E+00"},
{"2.459", 'E', 1, "2.5E+00"}, {"2.459", 100, 'E', 1, "2.5E+00"},
{"3.459", 'E', 2, "3.46E+00"}, {"3.459", 100, 'E', 2, "3.46E+00"},
{"4.459", 'E', 3, "4.459E+00"}, {"4.459", 100, 'E', 3, "4.459E+00"},
{"5.459", 'E', 4, "5.4590E+00"}, {"5.459", 100, 'E', 4, "5.4590E+00"},
{"1.459", 'f', 0, "1"}, {"1.459", 100, 'f', 0, "1"},
{"2.459", 'f', 1, "2.5"}, {"2.459", 100, 'f', 1, "2.5"},
{"3.459", 'f', 2, "3.46"}, {"3.459", 100, 'f', 2, "3.46"},
{"4.459", 'f', 3, "4.459"}, {"4.459", 100, 'f', 3, "4.459"},
{"5.459", 'f', 4, "5.4590"}, {"5.459", 100, 'f', 4, "5.4590"},
{"1.459", 'g', 0, "1"}, {"1.459", 100, 'g', 0, "1"},
{"2.459", 'g', 1, "2"}, {"2.459", 100, 'g', 1, "2"},
{"3.459", 'g', 2, "3.5"}, {"3.459", 100, 'g', 2, "3.5"},
{"4.459", 'g', 3, "4.46"}, {"4.459", 100, 'g', 3, "4.46"},
{"5.459", 'g', 4, "5.459"}, {"5.459", 100, 'g', 4, "5.459"},
{"1459", 'g', 0, "1e+03"}, {"1459", 53, 'g', 0, "1e+03"},
{"2459", 'g', 1, "2e+03"}, {"2459", 53, 'g', 1, "2e+03"},
{"3459", 'g', 2, "3.5e+03"}, {"3459", 53, 'g', 2, "3.5e+03"},
{"4459", 'g', 3, "4.46e+03"}, {"4459", 53, 'g', 3, "4.46e+03"},
{"5459", 'g', 4, "5459"}, {"5459", 53, 'g', 4, "5459"},
{"1459", 'G', 0, "1E+03"}, {"1459", 53, 'G', 0, "1E+03"},
{"2459", 'G', 1, "2E+03"}, {"2459", 53, 'G', 1, "2E+03"},
{"3459", 'G', 2, "3.5E+03"}, {"3459", 53, 'G', 2, "3.5E+03"},
{"4459", 'G', 3, "4.46E+03"}, {"4459", 53, 'G', 3, "4.46E+03"},
{"5459", 'G', 4, "5459"}, {"5459", 53, 'G', 4, "5459"},
{"3", 'e', 40, "3.0000000000000000000000000000000000000000e+00"}, {"3", 10, 'e', 40, "3.0000000000000000000000000000000000000000e+00"},
{"3", 'f', 40, "3.0000000000000000000000000000000000000000"}, {"3", 10, 'f', 40, "3.0000000000000000000000000000000000000000"},
{"3", 'g', 40, "3"}, {"3", 10, 'g', 40, "3"},
{"3e40", 'e', 40, "3.0000000000000000000000000000000000000000e+40"}, {"3e40", 100, 'e', 40, "3.0000000000000000000000000000000000000000e+40"},
{"3e40", 'f', 4, "30000000000000000000000000000000000000000.0000"}, {"3e40", 100, 'f', 4, "30000000000000000000000000000000000000000.0000"},
{"3e40", 'g', 40, "3e+40"}, {"3e40", 100, 'g', 40, "3e+40"},
// TODO(gri) need tests for actual large Floats // TODO(gri) need tests for actual large Floats
// These depend on the selected mantissa length to match strconv.FormatFloat. {"0", 53, 'b', 0, "0"},
// Disabled for now. {"-0", 53, 'b', 0, "-0"},
// {"0", 'b', 0, "0"}, {"1.0", 53, 'b', 0, "4503599627370496p-52"},
// {"-0", 'b', 0, "-0"}, {"-1.0", 53, 'b', 0, "-4503599627370496p-52"},
// {"1.0", 'b', 0, "4503599627370496p-52"}, {"4503599627370496", 53, 'b', 0, "4503599627370496p+0"},
// {"-1.0", 'b', 0, "-4503599627370496p-52"},
// {"4503599627370496", 'b', 0, "4503599627370496p+0"},
{"0", 'p', 0, "0"}, // issue 9939
{"-0", 'p', 0, "-0"}, {"3", 350, 'b', 0, "1720123961992553633708115671476565205597423741876210842803191629540192157066363606052513914832594264915968p-348"},
{"1024.0", 'p', 0, "0x.8p11"}, {"03", 350, 'b', 0, "1720123961992553633708115671476565205597423741876210842803191629540192157066363606052513914832594264915968p-348"},
{"-1024.0", 'p', 0, "-0x.8p11"}, {"3.", 350, 'b', 0, "1720123961992553633708115671476565205597423741876210842803191629540192157066363606052513914832594264915968p-348"},
{"3.0", 350, 'b', 0, "1720123961992553633708115671476565205597423741876210842803191629540192157066363606052513914832594264915968p-348"},
{"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"},
{"0", 64, 'p', 0, "0"},
{"-0", 64, 'p', 0, "-0"},
{"1024.0", 64, 'p', 0, "0x.8p11"},
{"-1024.0", 64, 'p', 0, "-0x.8p11"},
// unsupported format // unsupported format
{"3.14", 'x', 0, "%x"}, {"3.14", 64, 'x', 0, "%x"},
} { } {
f, _, err := ParseFloat(test.x, 0, 1000, ToNearestEven) f, _, err := ParseFloat(test.x, 0, test.prec, ToNearestEven)
if err != nil { if err != nil {
t.Errorf("%v: %s", test, err) t.Errorf("%v: %s", test, err)
continue continue
} }
got := f.Format(test.format, test.prec) got := f.Format(test.format, test.digits)
if got != test.want { if got != test.want {
t.Errorf("%v: got %s; want %s", test, got, test.want) t.Errorf("%v: got %s; want %s", test, got, test.want)
} }
// compare with strconv.FormatFloat output if possible
// ('p' format is not supported by strconv.FormatFloat,
// and its output for 0.0 prints a biased exponent value
// as in 0p-1074 which makes no sense to emulate here)
if test.prec == 53 && test.format != 'p' && f.Sign() != 0 {
f64, _ := f.Float64()
got := strconv.FormatFloat(f64, test.format, test.digits, 64)
if got != test.want {
t.Errorf("%v: got %s; want %s", test, got, test.want)
}
}
} }
} }