golang math 代码
文件路径：/src/runtime/internal/math/math.go
/ Copyright 2018 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
import "internal/goarch"
const MaxUintptr = ^uintptr(0)
/ MulUintptr returns a * b and whether the multiplication overflowed.
/ On supported platforms this is an intrinsic lowered by the compiler.
func MulUintptr(a, b uintptr) (uintptr, bool) {
if a|b < 1<<(4*goarch.PtrSize) || a == 0 {
return a * b, false
}
overflow := b > MaxUintptr/a
return a * b, overflow
}
/ Mul64 returns the 128-bit product of x and y: (hi, lo) = x * y
/ with the product bits' upper half returned in hi and the lower
/ half returned in lo.
/ This is a copy from math/bits.Mul64
/ On supported platforms this is an intrinsic lowered by the compiler.
func Mul64(x, y uint64) (hi, lo uint64) {
const mask32 = 1<<32 - 1
x0 := x & mask32
x1 := x >> 32
y0 := y & mask32
y1 := y >> 32
w0 := x0 * y0
t := x1*y0 + w0>>32
w1 := t & mask32
w2 := t >> 32
w1 += x0 * y1
hi = x1*y1 + w2 + w1>>32
lo = x * y
return
}