diff options
Diffstat (limited to 'libgo/go/math/pow.go')
| -rw-r--r-- | libgo/go/math/pow.go | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/libgo/go/math/pow.go b/libgo/go/math/pow.go index 7ba426f4..e255ee4 100644 --- a/libgo/go/math/pow.go +++ b/libgo/go/math/pow.go @@ -99,7 +99,16 @@ func pow(x, y float64) float64 { return NaN() } if yi >= 1<<63 { - return Exp(y * Log(x)) + // yi is a large even int that will lead to overflow (or underflow to 0) + // for all x except -1 (x == 1 was handled earlier) + switch { + case x == -1: + return 1 + case (Abs(x) < 1) == (y > 0): + return 0 + default: + return Inf(1) + } } // ans = a1 * 2**ae (= 1 for now). @@ -121,6 +130,15 @@ func pow(x, y float64) float64 { // accumulate powers of two into exp. x1, xe := Frexp(x) for i := int64(yi); i != 0; i >>= 1 { + if xe < -1<<12 || 1<<12 < xe { + // catch xe before it overflows the left shift below + // Since i !=0 it has at least one bit still set, so ae will accumulate xe + // on at least one more iteration, ae += xe is a lower bound on ae + // the lower bound on ae exceeds the size of a float64 exp + // so the final call to Ldexp will produce under/overflow (0/Inf) + ae += xe + break + } if i&1 == 1 { a1 *= x1 ae += xe |