From 800bb6fc53d9eb9f8db9a71ec4f09d72ae3e20da Mon Sep 17 00:00:00 2001
From: Paul Dee <itsascambutmailmeanyway@gmail.com>
Date: Sat, 18 Mar 2023 12:57:18 +0100
Subject: [PATCH] Updates to LOC type RFC1876 (#1440)

https://www.rfc-editor.org/rfc/rfc1876
---
 types.go      | 14 ++++++++------
 types_test.go | 14 +++++++-------
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/types.go b/types.go
index 1c7dc0976..03afeccda 100644
--- a/types.go
+++ b/types.go
@@ -198,7 +198,7 @@ const (
 	_CD = 1 << 4  // checking disabled
 )
 
-// Various constants used in the LOC RR. See RFC 1887.
+// Various constants used in the LOC RR. See RFC 1876.
 const (
 	LOC_EQUATOR       = 1 << 31 // RFC 1876, Section 2.
 	LOC_PRIMEMERIDIAN = 1 << 31 // RFC 1876, Section 2.
@@ -792,7 +792,10 @@ type LOC struct {
 
 // cmToM takes a cm value expressed in RFC 1876 SIZE mantissa/exponent
 // format and returns a string in m (two decimals for the cm).
-func cmToM(m, e uint8) string {
+func cmToM(x uint8) string {
+	m := x & 0xf0 >> 4
+	e := x & 0x0f
+
 	if e < 2 {
 		if e == 1 {
 			m *= 10
@@ -848,10 +851,9 @@ func (rr *LOC) String() string {
 		s += fmt.Sprintf("%.0fm ", alt)
 	}
 
-	s += cmToM(rr.Size&0xf0>>4, rr.Size&0x0f) + "m "
-	s += cmToM(rr.HorizPre&0xf0>>4, rr.HorizPre&0x0f) + "m "
-	s += cmToM(rr.VertPre&0xf0>>4, rr.VertPre&0x0f) + "m"
-
+	s += cmToM(rr.Size) + "m "
+	s += cmToM(rr.HorizPre) + "m "
+	s += cmToM(rr.VertPre) + "m"
 	return s
 }
 
diff --git a/types_test.go b/types_test.go
index b3f5583fa..32df35bf0 100644
--- a/types_test.go
+++ b/types_test.go
@@ -5,37 +5,37 @@ import (
 )
 
 func TestCmToM(t *testing.T) {
-	s := cmToM(0, 0)
+	s := cmToM((0 << 4) + 0)
 	if s != "0.00" {
 		t.Error("0, 0")
 	}
 
-	s = cmToM(1, 0)
+	s = cmToM((1 << 4) + 0)
 	if s != "0.01" {
 		t.Error("1, 0")
 	}
 
-	s = cmToM(3, 1)
+	s = cmToM((3 << 4) + 1)
 	if s != "0.30" {
 		t.Error("3, 1")
 	}
 
-	s = cmToM(4, 2)
+	s = cmToM((4 << 4) + 2)
 	if s != "4" {
 		t.Error("4, 2")
 	}
 
-	s = cmToM(5, 3)
+	s = cmToM((5 << 4) + 3)
 	if s != "50" {
 		t.Error("5, 3")
 	}
 
-	s = cmToM(7, 5)
+	s = cmToM((7 << 4) + 5)
 	if s != "7000" {
 		t.Error("7, 5")
 	}
 
-	s = cmToM(9, 9)
+	s = cmToM((9 << 4) + 9)
 	if s != "90000000" {
 		t.Error("9, 9")
 	}