diff options
Diffstat (limited to 'libgo/go/math/big/float.go')
| -rw-r--r-- | libgo/go/math/big/float.go | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/libgo/go/math/big/float.go b/libgo/go/math/big/float.go index aabd7b44777..7e11f1aff58 100644 --- a/libgo/go/math/big/float.go +++ b/libgo/go/math/big/float.go @@ -14,6 +14,7 @@ package big import ( "fmt" "math" + "math/bits" ) const debugFloat = false // enable for debugging @@ -97,7 +98,7 @@ const ( // the slice may (but doesn't have to) be shorter if the mantissa contains // trailing 0 bits. x.mant is normalized if the msb of x.mant == 1 (i.e., // the msb is shifted all the way "to the left"). Thus, if the mantissa has -// trailing 0 bits or x.prec is not a multiple of the the Word size _W, +// trailing 0 bits or x.prec is not a multiple of the Word size _W, // x.mant[0] has trailing zero bits. The msb of the mantissa corresponds // to the value 0.5; the exponent x.exp shifts the binary point as needed. // @@ -498,8 +499,8 @@ func (z *Float) setBits64(neg bool, x uint64) *Float { } // x != 0 z.form = finite - s := nlz64(x) - z.mant = z.mant.setUint64(x << s) + s := bits.LeadingZeros64(x) + z.mant = z.mant.setUint64(x << uint(s)) z.exp = int32(64 - s) // always fits if z.prec < 64 { z.round(0) @@ -1438,8 +1439,16 @@ func (z *Float) Add(x, y *Float) *Float { if x.form == finite && y.form == finite { // x + y (common case) + + // Below we set z.neg = x.neg, and when z aliases y this will + // change the y operand's sign. This is fine, because if an + // operand aliases the receiver it'll be overwritten, but we still + // want the original x.neg and y.neg values when we evaluate + // x.neg != y.neg, so we need to save y.neg before setting z.neg. + yneg := y.neg + z.neg = x.neg - if x.neg == y.neg { + if x.neg == yneg { // x + y == x + y // (-x) + (-y) == -(x + y) z.uadd(x, y) @@ -1501,8 +1510,9 @@ func (z *Float) Sub(x, y *Float) *Float { if x.form == finite && y.form == finite { // x - y (common case) + yneg := y.neg z.neg = x.neg - if x.neg != y.neg { + if x.neg != yneg { // x - (-y) == x + y // (-x) - y == -(x + y) z.uadd(x, y) |