add port of field operations assembler from libsecp256k1

field_amd64.go

@@ -0,0 +1,23 @@
+//go:build amd64
+
+package p256k1
+
+// fieldMulAsm multiplies two field elements using x86-64 assembly.
+// This is a direct port of bitcoin-core secp256k1_fe_mul_inner.
+// r, a, b are 5x52-bit limb representations.
+//
+//go:noescape
+func fieldMulAsm(r, a, b *FieldElement)
+
+// fieldSqrAsm squares a field element using x86-64 assembly.
+// This is a direct port of bitcoin-core secp256k1_fe_sqr_inner.
+// Squaring is optimized compared to multiplication.
+//
+//go:noescape
+func fieldSqrAsm(r, a *FieldElement)
+
+// hasFieldAsm returns true if field assembly is available.
+// On amd64, this is always true.
+func hasFieldAsm() bool {
+	return true
+}