math/big: permit passing of an *Int to Float.Int to avoid allocation
Change-Id: I50e83248357928e56c94b88a8764de828f4f5c76
Reviewed-on: https://go-review.googlesource.com/5890
Reviewed-by: Alan Donovan <adonovan@google.com>
diff --git a/src/math/big/float.go b/src/math/big/float.go
index 8fbe180..717c24d 100644
--- a/src/math/big/float.go
+++ b/src/math/big/float.go
@@ -788,13 +788,14 @@
// Int returns the result of truncating x towards zero; or nil
// if x is an infinity. The result is Exact if x.IsInt();
// otherwise it is Below for x > 0, and Above for x < 0.
-func (x *Float) Int() (res *Int, acc Accuracy) {
- // TODO(gri) accept z argument for result storage (see Float.Rat below)
+// If a non-nil *Int argument z is provided, it is used to store
+// the result; otherwise a new Int is allocated.
+func (x *Float) Int(z *Int) (*Int, Accuracy) {
if debugFloat {
validate(x)
}
// accuracy for inexact results
- acc = Below // truncation
+ acc := Below // truncation
if x.neg {
acc = Above
}
@@ -807,7 +808,11 @@
if len(x.mant) == 0 {
acc = Exact // ±0
}
- return new(Int), acc // ±0.xxx
+ // ±0.xxx
+ if z == nil {
+ return new(Int), acc
+ }
+ return z.SetUint64(0), acc
}
// x.exp > 0
// x.mant[len(x.mant)-1] != 0
@@ -818,17 +823,20 @@
acc = Exact
}
// shift mantissa as needed
- res = &Int{neg: x.neg}
+ if z == nil {
+ z = new(Int)
+ }
+ z.neg = x.neg
// TODO(gri) should have a shift that takes positive and negative shift counts
switch {
case exp > allBits:
- res.abs = res.abs.shl(x.mant, exp-allBits)
+ z.abs = z.abs.shl(x.mant, exp-allBits)
default:
- res.abs = res.abs.set(x.mant)
+ z.abs = z.abs.set(x.mant)
case exp < allBits:
- res.abs = res.abs.shr(x.mant, allBits-exp)
+ z.abs = z.abs.shr(x.mant, allBits-exp)
}
- return
+ return z, acc
}
// Rat returns x converted into an exact fraction; or nil if x is an infinity.
diff --git a/src/math/big/float_test.go b/src/math/big/float_test.go
index 69e88c3..6391bee 100644
--- a/src/math/big/float_test.go
+++ b/src/math/big/float_test.go
@@ -714,7 +714,7 @@
{"1e+100", "10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", Exact},
} {
x := makeFloat(test.x)
- res, acc := x.Int()
+ res, acc := x.Int(nil)
got := "nil"
if res != nil {
got = res.String()
@@ -723,6 +723,15 @@
t.Errorf("%s: got %s (%s); want %s (%s)", test.x, got, acc, test.want, test.acc)
}
}
+
+ // check that supplied *Int is used
+ for _, f := range []string{"0", "1", "-1", "1234"} {
+ x := makeFloat(f)
+ i := new(Int)
+ if res, _ := x.Int(i); res != i {
+ t.Errorf("(%s).Int is not using supplied *Int", f)
+ }
+ }
}
func TestFloatRat(t *testing.T) {
@@ -765,7 +774,7 @@
}
// check that supplied *Rat is used
- for _, f := range []string{"0", "1"} {
+ for _, f := range []string{"0", "1", "-1", "1234"} {
x := makeFloat(f)
r := new(Rat)
if res := x.Rat(r); res != r {
