golang p521_invert 代码
文件路径：/src/crypto/internal/nistec/fiat/p521_invert.go
/ Copyright 2021 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.
/ Code generated by addchain. DO NOT EDIT.
package fiat
/ Invert sets e = 1/x, and returns e.
/
/ If x == 0, Invert returns e = 0.
func (e *P521Element) Invert(x *P521Element) *P521Element {
/ Inversion is implemented as exponentiation with exponent p − 2.
/ The sequence of 13 multiplications and 520 squarings is derived from the
/ following addition chain generated with github.com/mmcloughlin/addchain v0.3.0.
/
/ _10 = 2*1
/ _11 = 1 + _10
/ _1100 = _11 << 2
/ _1111 = _11 + _1100
/ _11110000 = _1111 << 4
/ _11111111 = _1111 + _11110000
/ x16 = _11111111 << 8 + _11111111
/ x32 = x16 << 16 + x16
/ x64 = x32 << 32 + x32
/ x65 = 2*x64 + 1
/ x129 = x65 << 64 + x64
/ x130 = 2*x129 + 1
/ x259 = x130 << 129 + x129
/ x260 = 2*x259 + 1
/ x519 = x260 << 259 + x259
/ return x519 << 2 + 1
/
var z = new(P521Element).Set(e)
var t0 = new(P521Element)
z.Square(x)
z.Mul(x, z)
t0.Square(z)
for s := 1; s < 2; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
t0.Square(z)
for s := 1; s < 4; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
t0.Square(z)
for s := 1; s < 8; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
t0.Square(z)
for s := 1; s < 16; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
t0.Square(z)
for s := 1; s < 32; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
t0.Square(z)
t0.Mul(x, t0)
for s := 0; s < 64; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
t0.Square(z)
t0.Mul(x, t0)
for s := 0; s < 129; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
t0.Square(z)
t0.Mul(x, t0)
for s := 0; s < 259; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
for s := 0; s < 2; s++ {
z.Square(z)
}
z.Mul(x, z)
return e.Set(z)
}