golang p256_invert 代码
文件路径：/src/crypto/internal/nistec/fiat/p256_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 *P256Element) Invert(x *P256Element) *P256Element {
/ Inversion is implemented as exponentiation with exponent p − 2.
/ The sequence of 12 multiplications and 255 squarings is derived from the
/ following addition chain generated with github.com/mmcloughlin/addchain v0.4.0.
/
/ _10 = 2*1
/ _11 = 1 + _10
/ _110 = 2*_11
/ _111 = 1 + _110
/ _111000 = _111 << 3
/ _111111 = _111 + _111000
/ x12 = _111111 << 6 + _111111
/ x15 = x12 << 3 + _111
/ x16 = 2*x15 + 1
/ x32 = x16 << 16 + x16
/ i53 = x32 << 15
/ x47 = x15 + i53
/ i263 = ((i53 << 17 + 1) << 143 + x47) << 47
/ return (x47 + i263) << 2 + 1
/
var z = new(P256Element).Set(e)
var t0 = new(P256Element)
var t1 = new(P256Element)
z.Square(x)
z.Mul(x, z)
z.Square(z)
z.Mul(x, z)
t0.Square(z)
for s := 1; s < 3; s++ {
t0.Square(t0)
}
t0.Mul(z, t0)
t1.Square(t0)
for s := 1; s < 6; s++ {
t1.Square(t1)
}
t0.Mul(t0, t1)
for s := 0; s < 3; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
t0.Square(z)
t0.Mul(x, t0)
t1.Square(t0)
for s := 1; s < 16; s++ {
t1.Square(t1)
}
t0.Mul(t0, t1)
for s := 0; s < 15; s++ {
t0.Square(t0)
}
z.Mul(z, t0)
for s := 0; s < 17; s++ {
t0.Square(t0)
}
t0.Mul(x, t0)
for s := 0; s < 143; s++ {
t0.Square(t0)
}
t0.Mul(z, t0)
for s := 0; s < 47; 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)
}