golang signbit 代码
文件路径：/src/math/signbit.go
/ Copyright 2010 The Go Authors. All rights reserved.
/ Use of this source code is governed by a BSD-style
/ license that can be found in the LICENSE file.
package math
/ Signbit reports whether x is negative or negative zero.
func Signbit(x float64) bool {
return Float64bits(x)&(1<<63) != 0
}