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Diffstat (limited to 'src/crypto/internal/nistec/fiat/p256_invert.go')
-rw-r--r--src/crypto/internal/nistec/fiat/p256_invert.go84
1 files changed, 84 insertions, 0 deletions
diff --git a/src/crypto/internal/nistec/fiat/p256_invert.go b/src/crypto/internal/nistec/fiat/p256_invert.go
new file mode 100644
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+++ b/src/crypto/internal/nistec/fiat/p256_invert.go
@@ -0,0 +1,84 @@
+// 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)
+}