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math/big: wrap Float.Cmp result in struct to prevent wrong use

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Float.Cmp used to return a value < 0, 0, or > 0 depending on how
arguments x, y compared against each other. With the possibility
of NaNs, the result was changed into an Accuracy (to include Undef).
Consequently, Float.Cmp results could still be compared for (in-)
equality with 0, but comparing if < 0 or > 0 would provide the
wrong answer w/o any obvious notice by the compiler.

This change wraps Float.Cmp results into a struct and accessors
are used to access the desired result. This prevents incorrect
use.

Change-Id: I34e6a6c1859251ec99b5cf953e82542025ace56f
Reviewed-on: https://go-review.googlesource.com/7526
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Robert Griesemer 2015-03-13 17:24:30 -07:00
parent b100216441
commit 23fd374bf2
4 changed files with 30 additions and 25 deletions
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31
src/math/big/float.go
View File

@ -1446,6 +1446,10 @@ func (z *Float) Quo(x, y *Float) *Float {
return z
}
type cmpResult struct {
acc Accuracy
}
// Cmp compares x and y and returns:
//
// Below if x < y
@ -1453,44 +1457,45 @@ func (z *Float) Quo(x, y *Float) *Float {
// Above if x > y
// Undef if any of x, y is NaN
//
func (x *Float) Cmp(y *Float) Accuracy {
func (x *Float) Cmp(y *Float) cmpResult {
if debugFloat {
x.validate()
y.validate()
}
if x.form == nan || y.form == nan {
return Undef
return cmpResult{Undef}
}
mx := x.ord()
my := y.ord()
switch {
case mx < my:
return Below
return cmpResult{Below}
case mx > my:
return Above
return cmpResult{Above}
}
// mx == my
// only if |mx| == 1 we have to compare the mantissae
switch mx {
case -1:
return y.ucmp(x)
return cmpResult{y.ucmp(x)}
case +1:
return x.ucmp(y)
return cmpResult{x.ucmp(y)}
}
return Exact
return cmpResult{Exact}
}
// The following accessors simplify testing of Cmp results.
func (acc Accuracy) Eql() bool { return acc == Exact }
func (acc Accuracy) Neq() bool { return acc != Exact }
func (acc Accuracy) Lss() bool { return acc == Below }
func (acc Accuracy) Leq() bool { return acc&Above == 0 }
func (acc Accuracy) Gtr() bool { return acc == Above }
func (acc Accuracy) Geq() bool { return acc&Below == 0 }
func (res cmpResult) Acc() Accuracy { return res.acc }
func (res cmpResult) Eql() bool { return res.acc == Exact }
func (res cmpResult) Neq() bool { return res.acc != Exact }
func (res cmpResult) Lss() bool { return res.acc == Below }
func (res cmpResult) Leq() bool { return res.acc&Above == 0 }
func (res cmpResult) Gtr() bool { return res.acc == Above }
func (res cmpResult) Geq() bool { return res.acc&Below == 0 }
// ord classifies x and returns:
//

20
src/math/big/float_test.go
View File

@ -207,7 +207,7 @@ func feq(x, y *Float) bool {
if x.IsNaN() || y.IsNaN() {
return x.IsNaN() && y.IsNaN()
}
return x.Cmp(y) == 0 && x.IsNeg() == y.IsNeg()
return x.Cmp(y).Eql() && x.IsNeg() == y.IsNeg()
}
func TestFloatMantExp(t *testing.T) {
@ -918,7 +918,7 @@ func TestFloatRat(t *testing.T) {
// inverse conversion
if res != nil {
got := new(Float).SetPrec(64).SetRat(res)
if got.Cmp(x) != 0 {
if got.Cmp(x).Neq() {
t.Errorf("%s: got %s; want %s", test.x, got, x)
}
}
@ -995,7 +995,7 @@ func TestFloatInc(t *testing.T) {
for i := 0; i < n; i++ {
x.Add(&x, &one)
}
if x.Cmp(new(Float).SetInt64(n)) != 0 {
if x.Cmp(new(Float).SetInt64(n)).Neq() {
t.Errorf("prec = %d: got %s; want %d", prec, &x, n)
}
}
@ -1036,14 +1036,14 @@ func TestFloatAdd(t *testing.T) {
got := new(Float).SetPrec(prec).SetMode(mode)
got.Add(x, y)
want := zbits.round(prec, mode)
if got.Cmp(want) != 0 {
if got.Cmp(want).Neq() {
t.Errorf("i = %d, prec = %d, %s:\n\t %s %v\n\t+ %s %v\n\t= %s\n\twant %s",
i, prec, mode, x, xbits, y, ybits, got, want)
}
got.Sub(z, x)
want = ybits.round(prec, mode)
if got.Cmp(want) != 0 {
if got.Cmp(want).Neq() {
t.Errorf("i = %d, prec = %d, %s:\n\t %s %v\n\t- %s %v\n\t= %s\n\twant %s",
i, prec, mode, z, zbits, x, xbits, got, want)
}
@ -1137,7 +1137,7 @@ func TestFloatMul(t *testing.T) {
got := new(Float).SetPrec(prec).SetMode(mode)
got.Mul(x, y)
want := zbits.round(prec, mode)
if got.Cmp(want) != 0 {
if got.Cmp(want).Neq() {
t.Errorf("i = %d, prec = %d, %s:\n\t %s %v\n\t* %s %v\n\t= %s\n\twant %s",
i, prec, mode, x, xbits, y, ybits, got, want)
}
@ -1147,7 +1147,7 @@ func TestFloatMul(t *testing.T) {
}
got.Quo(z, x)
want = ybits.round(prec, mode)
if got.Cmp(want) != 0 {
if got.Cmp(want).Neq() {
t.Errorf("i = %d, prec = %d, %s:\n\t %s %v\n\t/ %s %v\n\t= %s\n\twant %s",
i, prec, mode, z, zbits, x, xbits, got, want)
}
@ -1230,7 +1230,7 @@ func TestIssue6866(t *testing.T) {
p.Mul(p, psix)
z2.Sub(two, p)
if z1.Cmp(z2) != 0 {
if z1.Cmp(z2).Neq() {
t.Fatalf("prec %d: got z1 = %s != z2 = %s; want z1 == z2\n", prec, z1, z2)
}
if z1.Sign() != 0 {
@ -1281,7 +1281,7 @@ func TestFloatQuo(t *testing.T) {
prec := uint(preci + d)
got := new(Float).SetPrec(prec).SetMode(mode).Quo(x, y)
want := bits.round(prec, mode)
if got.Cmp(want) != 0 {
if got.Cmp(want).Neq() {
t.Errorf("i = %d, prec = %d, %s:\n\t %s\n\t/ %s\n\t= %s\n\twant %s",
i, prec, mode, x, y, got, want)
}
@ -1462,7 +1462,7 @@ func TestFloatCmpSpecialValues(t *testing.T) {
}
for _, y := range args {
yy.SetFloat64(y)
got := xx.Cmp(yy)
got := xx.Cmp(yy).Acc()
want := Undef
switch {
case x < y:

2
src/math/big/floatconv_test.go
View File

@ -102,7 +102,7 @@ func TestFloatSetFloat64String(t *testing.T) {
}
f, _ := x.Float64()
want := new(Float).SetFloat64(test.x)
if x.Cmp(want) != 0 {
if x.Cmp(want).Neq() {
t.Errorf("%s: got %s (%v); want %v", test.s, &x, f, test.x)
}
}

2
src/math/big/floatexample_test.go
View File

@ -63,7 +63,7 @@ func ExampleFloat_Cmp() {
t := x.Cmp(y)
fmt.Printf(
"%4s %4s %5s %c %c %c %c %c %c\n",
x, y, t,
x, y, t.Acc(),
mark(t.Eql()), mark(t.Neq()), mark(t.Lss()), mark(t.Leq()), mark(t.Gtr()), mark(t.Geq()))
}
fmt.Println()