1 files changed, 73 insertions, 0 deletions
diff --git a/src/crypto/elliptic/gen_p256_table.go b/src/crypto/elliptic/gen_p256_table.go
new file mode 100644
index 0000000..0ebbc66
--- /dev/null
+++ b/src/crypto/elliptic/gen_p256_table.go
@@ -0,0 +1,73 @@
+// 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.
+
+//go:build ignore
+
+package main
+
+import (
+	"crypto/elliptic"
+	"encoding/binary"
+	"log"
+	"os"
+)
+
+func main() {
+	// Generate precomputed p256 tables.
+	var pre [43][32 * 8]uint64
+	basePoint := []uint64{
+		0x79e730d418a9143c, 0x75ba95fc5fedb601, 0x79fb732b77622510, 0x18905f76a53755c6,
+		0xddf25357ce95560a, 0x8b4ab8e4ba19e45c, 0xd2e88688dd21f325, 0x8571ff1825885d85,
+		0x0000000000000001, 0xffffffff00000000, 0xffffffffffffffff, 0x00000000fffffffe,
+	}
+	t1 := make([]uint64, 12)
+	t2 := make([]uint64, 12)
+	copy(t2, basePoint)
+	zInv := make([]uint64, 4)
+	zInvSq := make([]uint64, 4)
+	for j := 0; j < 32; j++ {
+		copy(t1, t2)
+		for i := 0; i < 43; i++ {
+			// The window size is 6 so we need to double 6 times.
+			if i != 0 {
+				for k := 0; k < 6; k++ {
+					elliptic.P256PointDoubleAsm(t1, t1)
+				}
+			}
+			// Convert the point to affine form. (Its values are
+			// still in Montgomery form however.)
+			elliptic.P256Inverse(zInv, t1[8:12])
+			elliptic.P256Sqr(zInvSq, zInv, 1)
+			elliptic.P256Mul(zInv, zInv, zInvSq)
+			elliptic.P256Mul(t1[:4], t1[:4], zInvSq)
+			elliptic.P256Mul(t1[4:8], t1[4:8], zInv)
+			copy(t1[8:12], basePoint[8:12])
+			// Update the table entry
+			copy(pre[i][j*8:], t1[:8])
+		}
+		if j == 0 {
+			elliptic.P256PointDoubleAsm(t2, basePoint)
+		} else {
+			elliptic.P256PointAddAsm(t2, t2, basePoint)
+		}
+	}
+
+	var bin []byte
+
+	// Dump the precomputed tables, flattened, little-endian.
+	// These tables are used directly by assembly on little-endian platforms.
+	// go:embedding the data into a string lets it be stored readonly.
+	for i := range &pre {
+		for _, v := range &pre[i] {
+			var u8 [8]byte
+			binary.LittleEndian.PutUint64(u8[:], v)
+			bin = append(bin, u8[:]...)
+		}
+	}
+
+	err := os.WriteFile("p256_asm_table.bin", bin, 0644)
+	if err != nil {
+		log.Fatal(err)
+	}
+}