field arithmetic cleanup

Co-authored-by: Armando Faz <armfazh@users.noreply.github.com>

Author: whyvl

math/gf4096/gf4096.go

@@ -2,11 +2,11 @@
 package gf4096
 
 // Gf is a field element of characteristic 2 modulo z^12 + z^3 + 1
-type Gf = uint16
+type Elt = uint16
 
 const (
-	GfBits = 12
-	GfMask = (1 << GfBits) - 1
+	Bits = 12
+	Mask = (1 << Bits) - 1
 )
 
 // Add two Gf elements together. Since an addition in Gf(2) is the same as XOR,
@@ -37,7 +37,7 @@ func Mul(a, b Gf) Gf {
 	tmp ^= t >> 9
 	tmp ^= t >> 12
 
-	return uint16(tmp & GfMask)
+	return Elt(tmp & Mask)
 }
 
 // sqr calculates the square of Gf element a

math/gf4096/gf_test.go

@@ -17,7 +17,7 @@ type (
 func assertEq(t *testing.T, a, b Gf) {
     t.Helper()
 	if a != b {
-		test.ReportError(t, b, a)
+		test.ReportError(t, a, b)
 	}
 }