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math/big: correctly handle large exponent in SetString

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Even though the umul/uquo functions expect two valid, finite big.Floats
arguments, SetString was calling them with possibly Inf values, which
resulted in bogus return values.

Replace umul and udiv calls with Mul and Quo calls to fix this. Also,
fix two wrong tests.

See relevant issue on issue tracker for a detailed explanation.

Fixes #11341

Change-Id: Ie35222763a57a2d712a5f5f7baec75cab8189a53
Reviewed-on: https://go-review.googlesource.com/13778
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Alberto Donizetti 2015-08-21 19:17:18 +02:00 committed by Robert Griesemer
parent 92eb34b59a
commit 13b5dc885b
2 changed files with 4 additions and 4 deletions
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4
src/math/big/floatconv.go
View File

@ -125,9 +125,9 @@ func (z *Float) scan(r io.ByteScanner, base int) (f *Float, b int, err error) {
// apply 10**exp10
p := new(Float).SetPrec(z.Prec() + 64) // use more bits for p -- TODO(gri) what is the right number?
if exp10 < 0 {
z.uquo(z, p.pow10(-exp10))
z.Quo(z, p.pow10(-exp10))
} else {
z.umul(z, p.pow10(exp10))
z.Mul(z, p.pow10(exp10))
}
return

4
src/math/big/floatconv_test.go
View File

@ -367,9 +367,9 @@ func TestFloatText(t *testing.T) {
// make sure "stupid" exponents don't stall the machine
{"1e1000000", 64, 'p', 0, "0x.88b3a28a05eade3ap+3321929"},
{"1e1000000000", 64, 'p', 0, "0x.ecc5f45aa573d3p+1538481529"},
{"1e1000000000", 64, 'p', 0, "+Inf"},
{"1e-1000000", 64, 'p', 0, "0x.efb4542cc8ca418ap-3321928"},
{"1e-1000000000", 64, 'p', 0, "0x.8a64dd983a4c7dabp-1538481528"},
{"1e-1000000000", 64, 'p', 0, "0"},
// TODO(gri) need tests for actual large Floats