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cmd/compile: don't panic in complex division

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Updates #20227

Change-Id: Idadc3137490181a5d380367660cee21e8313cf3b
Reviewed-on: https://go-review.googlesource.com/42650
Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Alberto Donizetti 2017-05-04 11:25:01 +02:00
parent c7cae34b19
commit 2d1829b539
3 changed files with 34 additions and 4 deletions
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21
src/cmd/compile/internal/gc/const.go
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@ -1037,15 +1037,13 @@ func evconst(n *Node) {
cmplxmpy(v.U.(*Mpcplx), rv.U.(*Mpcplx))
case ODIV_ | CTCPLX_:
if rv.U.(*Mpcplx).Real.CmpFloat64(0) == 0 && rv.U.(*Mpcplx).Imag.CmpFloat64(0) == 0 {
if !cmplxdiv(v.U.(*Mpcplx), rv.U.(*Mpcplx)) {
yyerror("complex division by zero")
rv.U.(*Mpcplx).Real.SetFloat64(1.0)
rv.U.(*Mpcplx).Imag.SetFloat64(0.0)
break
}
cmplxdiv(v.U.(*Mpcplx), rv.U.(*Mpcplx))
case OEQ_ | CTNIL_:
goto settrue
@ -1591,7 +1589,11 @@ func cmplxmpy(v *Mpcplx, rv *Mpcplx) {
// complex divide v /= rv
// (a, b) / (c, d) = ((a*c + b*d), (b*c - a*d))/(c*c + d*d)
func cmplxdiv(v *Mpcplx, rv *Mpcplx) {
func cmplxdiv(v *Mpcplx, rv *Mpcplx) bool {
if rv.Real.CmpFloat64(0) == 0 && rv.Imag.CmpFloat64(0) == 0 {
return false
}
var ac Mpflt
var bd Mpflt
var bc Mpflt
@ -1599,6 +1601,7 @@ func cmplxdiv(v *Mpcplx, rv *Mpcplx) {
var cc_plus_dd Mpflt
cc_plus_dd.Set(&rv.Real)
cc_plus_dd.Mul(&rv.Real) // cc
ac.Set(&rv.Imag)
@ -1607,6 +1610,14 @@ func cmplxdiv(v *Mpcplx, rv *Mpcplx) {
cc_plus_dd.Add(&ac) // cc+dd
// We already checked that c and d are not both zero, but we can't
// assume that c²+d² != 0 follows, because for tiny values of c
// and/or d c²+d² can underflow to zero. Check that c²+d² is
// nonzero,return if it's not.
if cc_plus_dd.CmpFloat64(0) == 0 {
return false
}
ac.Set(&v.Real)
ac.Mul(&rv.Real) // ac
@ -1632,6 +1643,8 @@ func cmplxdiv(v *Mpcplx, rv *Mpcplx) {
v.Imag.Sub(&ad) // bc-ad
v.Imag.Quo(&cc_plus_dd) // (bc+ad)/(cc+dd)
return true
}
// Is n a Go language constant (as opposed to a compile-time constant)?