Add benchmarking for Schnorr signature verification

This commit introduces a new benchmark function, `BenchmarkSchnorrVerify`, in `schnorr_test.go` to evaluate the performance of the Schnorr signature verification process. Additionally, it optimizes the `SchnorrVerify` function in `schnorr.go` by implementing a global precomputed context, reducing overhead during verification calls. The changes aim to enhance performance and provide insights into the efficiency of the verification process.

schnorr.go

@@ -2,6 +2,7 @@ package p256k1
 
 import (
 	"errors"
+	"sync"
 	"unsafe"
 )
 
@@ -22,6 +23,27 @@ var zeroMask = [32]byte{
 	170, 247, 175, 105, 39, 10, 165, 20,
 }
 
+// Global precomputed context for Schnorr verification
+// This eliminates the overhead of context creation per verification call
+var (
+	schnorrVerifyContext     *secp256k1_context
+	schnorrVerifyContextOnce sync.Once
+)
+
+// initSchnorrVerifyContext initializes the global Schnorr verification context
+func initSchnorrVerifyContext() {
+	schnorrVerifyContext = &secp256k1_context{
+		ecmult_gen_ctx: secp256k1_ecmult_gen_context{built: 1},
+		declassify:     0,
+	}
+}
+
+// getSchnorrVerifyContext returns the precomputed Schnorr verification context
+func getSchnorrVerifyContext() *secp256k1_context {
+	schnorrVerifyContextOnce.Do(initSchnorrVerifyContext)
+	return schnorrVerifyContext
+}
+
 // NonceFunctionBIP340 implements BIP-340 nonce generation
 func NonceFunctionBIP340(nonce32 []byte, msg []byte, key32 []byte, xonlyPk32 []byte, auxRand32 []byte) error {
 	if len(nonce32) != 32 {
@@ -295,6 +317,7 @@ func SchnorrVerifyOld(sig64 []byte, msg32 []byte, xonlyPubkey *XOnlyPubkey) bool
 
 // SchnorrVerify verifies a Schnorr signature following BIP-340.
 // This is the new implementation translated from C secp256k1_schnorrsig_verify.
+// Uses precomputed context for optimal performance.
 func SchnorrVerify(sig64 []byte, msg32 []byte, xonlyPubkey *XOnlyPubkey) bool {
 	if len(sig64) != 64 {
 		return false
@@ -306,11 +329,8 @@ func SchnorrVerify(sig64 []byte, msg32 []byte, xonlyPubkey *XOnlyPubkey) bool {
 		return false
 	}
 
-	// Create a context (required by secp256k1_schnorrsig_verify)
-	ctx := &secp256k1_context{
-		ecmult_gen_ctx: secp256k1_ecmult_gen_context{built: 1},
-		declassify:     0,
-	}
+	// Use precomputed context (initialized once, reused across calls)
+	ctx := getSchnorrVerifyContext()
 
 	// Convert x-only pubkey to secp256k1_xonly_pubkey format
 	var secp_xonly secp256k1_xonly_pubkey

schnorr_test.go

@@ -236,3 +236,39 @@ func TestSchnorrMultipleSignatures(t *testing.T) {
 		t.Error("with different aux_rand, signatures should differ")
 	}
 }
+
+func BenchmarkSchnorrVerify(b *testing.B) {
+	// Generate keypair
+	kp, err := KeyPairGenerate()
+	if err != nil {
+		b.Fatalf("failed to generate keypair: %v", err)
+	}
+	defer kp.Clear()
+
+	// Get x-only pubkey
+	xonly, err := kp.XOnlyPubkey()
+	if err != nil {
+		b.Fatalf("failed to get x-only pubkey: %v", err)
+	}
+
+	// Create message
+	msg := make([]byte, 32)
+	for i := range msg {
+		msg[i] = byte(i)
+	}
+
+	// Sign
+	var sig [64]byte
+	if err := SchnorrSign(sig[:], msg, kp, nil); err != nil {
+		b.Fatalf("failed to sign: %v", err)
+	}
+
+	// Benchmark verification
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		if !SchnorrVerify(sig[:], msg, xonly) {
+			b.Fatal("verification failed")
+		}
+	}
+}

verify.go

@@ -2,6 +2,8 @@ package p256k1
 
 import (
 	"crypto/sha256"
+	"hash"
+	"sync"
 	"unsafe"
 )
 
@@ -667,6 +669,23 @@ func secp256k1_gej_add_zinv_var(r *secp256k1_gej, a *secp256k1_gej, b *secp256k1
 	secp256k1_gej_add_ge_var(r, a, b, nil)
 }
 
+// ============================================================================
+// GLOBAL PRE-ALLOCATED RESOURCES
+// ============================================================================
+
+// Global pre-allocated hash context for challenge computation to avoid allocations
+var (
+	challengeHashContext     hash.Hash
+	challengeHashContextOnce sync.Once
+)
+
+func getChallengeHashContext() hash.Hash {
+	challengeHashContextOnce.Do(func() {
+		challengeHashContext = sha256.New()
+	})
+	return challengeHashContext
+}
+
 // ============================================================================
 // EC MULTIPLICATION OPERATIONS
 // ============================================================================
@@ -899,14 +918,16 @@ func secp256k1_schnorrsig_sha256_tagged(sha *secp256k1_sha256) {
 
 // secp256k1_schnorrsig_challenge computes challenge hash
 func secp256k1_schnorrsig_challenge(e *secp256k1_scalar, r32 []byte, msg []byte, msglen int, pubkey32 []byte) {
-	// Optimized challenge computation - avoid allocations by writing directly to hash
+	// Optimized challenge computation using pre-allocated hash context to avoid allocations
 	var challengeHash [32]byte
 
 	// First hash: SHA256(tag)
 	tagHash := sha256.Sum256(bip340ChallengeTag)
 
 	// Second hash: SHA256(SHA256(tag) || SHA256(tag) || r32 || pubkey32 || msg)
-	h := sha256.New()
+	// Use pre-allocated hash context to avoid allocations
+	h := getChallengeHashContext()
+	h.Reset()
 	h.Write(tagHash[:])    // SHA256(tag)
 	h.Write(tagHash[:])    // SHA256(tag) again
 	h.Write(r32[:32])      // r32