Reverse bit order in Truth.Val

I.e. now the 0th bit corresponds to 'z' and the 51st bit corresponds to
'A' if every letter is used.

This allows us to display each atomic in alphabetical order in a truth
table yet still have the rows count up as if they were a binary number
(i.e. {0-0, 0-1, 1-0, 1-1} order instead of {0-0, 1-0, 0-1, 1-1}, which
is what it was before), yet still be able to iterate through all the
truth value sets via incrementing Truth.Val.

parse.go

@@ -25,8 +25,6 @@ type Truth struct {
 	Names    []byte
 }
 
-// TODO: fix (reverse) shift mapping
-
 func (t Truth) get(stmt byte) bool {
 	return t.Val&(1<<t.shiftMap[alphaToIdx(stmt)]) > 0
 }
@@ -54,7 +52,12 @@ func newTruth(atomics uint64) Truth {
 	var shiftMap [52]byte
 	names := make([]byte, 0, 52)
 	var shift byte
-	for i := byte(0); i < 52; i++ {
+	// Here we count down from 51 instead of up from 0 to effectively reverse the bit order in Truth.Val.
+	// This allows us to display each atomic in alphabetical order in a truth table and not have the rows "appear
+	// backwards" (e.g. {0-0, 1-0, 0-1, 1-1} instead of {0-0, 0-1, 1-0, 1-1}) yet still be able to count up by simply
+	// incrementing Truth.Val.
+	// Less than 52 in condition because of wrap around.
+	for i := byte(51); i < 52; i-- {
 		if atomics&(1<<i) > 0 {
 			shiftMap[i] = shift
 			shift++

parse_test.go

@@ -15,15 +15,15 @@ func TestParseEval(t *testing.T) {
 		{"a&b", []bool{false, false, false, true}},
 		{"a|b", []bool{false, true, true, true}},
 		{"a^b", []bool{false, true, true, false}},
-		{"a>b", []bool{true, false, true, true}},
+		{"a>b", []bool{true, true, false, true}},
 		{"a=b", []bool{true, false, false, true}},
 		{"0", []bool{false}},
 		{"1", []bool{true}},
 		{"a|!0", []bool{true, true}},
 		{"(a & b)", []bool{false, false, false, true}},
-		{"!(a > b)", []bool{false, true, false, false}},
+		{"!(a > b)", []bool{false, false, true, false}},
 		{"!!(a = b)", []bool{true, false, false, true}},
-		{"(a = b) | b", []bool{true, false, true, true}},
+		{"(a = b) | b", []bool{true, true, false, true}},
 	} {
 		stmt, truth, err := Parse(c.input)
 		if err != nil {

truthtable.go

@@ -95,9 +95,9 @@ func printLine(nAtomics int, outputWidth int, out io.Writer, rowSep string, l st
 func printHeader(atomics []byte, stmt string, out io.Writer, cs *CharSet) error {
 	var sb strings.Builder
 	sb.Grow(calcInputWidth(len(atomics)))
-	for i, a := range atomics {
-		sb.WriteByte(a)
-		if i < len(atomics)-1 {
+	for i := len(atomics) - 1; i >= 0; i-- {
+		sb.WriteByte(atomics[i])
+		if i > 0 {
 			sb.WriteString("  ")
 		}
 	}
@@ -113,9 +113,9 @@ func colourize(val bool) string {
 
 func printData(truth uint64, nAtomics int, output bool, outputWidth int, out io.Writer, cs *CharSet) error {
 	var sb strings.Builder
-	for i := 0; i < nAtomics; i++ {
+	for i := nAtomics - 1; i >= 0; i-- {
 		sb.WriteString(colourize(truth&(1<<i) > 0))
-		if i < nAtomics-1 {
+		if i > 0 {
 			sb.WriteString("  ")
 		}
 	}