initial commit. not currently in a working state.

1 files changed, 147 insertions, 0 deletions

diff --git a/nexgb/xgbgen/xml_fields.go b/nexgb/xgbgen/xml_fields.go
new file mode 100644
index 0000000..18be6e3
--- /dev/null
+++ b/nexgb/xgbgen/xml_fields.go
@@ -0,0 +1,147 @@
+package main
+/*
+	A series of fields should be taken as "structure contents", and *not*
+	just the single 'field' elements. Namely, 'fields' subsumes 'field'
+	elements.
+
+	More particularly, 'fields' corresponds to list, in order, of any of the
+	follow elements: pad, field, list, localfield, exprfield, valueparm
+	and switch.
+
+	Thus, the 'Field' type must contain the union of information corresponding
+	to all aforementioned fields.
+
+	This would ideally be a better job for interfaces, but I could not figure
+	out how to make them jive with Go's XML package. (And I don't really feel
+	up to type translation.)
+*/
+
+import (
+	"encoding/xml"
+	"fmt"
+	"log"
+	"strings"
+)
+
+type Field struct {
+	XMLName xml.Name
+
+	// For 'pad' element
+	Bytes int `xml:"bytes,attr"`
+
+	// For 'field', 'list', 'localfield', 'exprfield' and 'switch' elements.
+	Name string `xml:"name,attr"`
+
+	// For 'field', 'list', 'localfield', and 'exprfield' elements.
+	Type Type `xml:"type,attr"`
+
+	// For 'list', 'exprfield' and 'switch' elements.
+	Expr *Expression `xml:",any"`
+
+	// For 'valueparm' element.
+	ValueMaskType Type `xml:"value-mask-type,attr"`
+	ValueMaskName string `xml:"value-mask-name,attr"`
+	ValueListName string `xml:"value-list-name,attr"`
+
+	// For 'switch' element.
+	Bitcases []*Bitcase `xml:"bitcase"`
+
+	// I don't know which elements these are for. The documentation is vague.
+	// They also seem to be completely optional.
+	OptEnum Type `xml:"enum,attr"`
+	OptMask Type `xml:"mask,attr"`
+	OptAltEnum Type `xml:"altenum,attr"`
+}
+
+// String is for debugging purposes.
+func (f *Field) String() string {
+	switch f.XMLName.Local {
+	case "pad":
+		return fmt.Sprintf("pad (%d bytes)", f.Bytes)
+	case "field":
+		return fmt.Sprintf("field (type = '%s', name = '%s')", f.Type, f.Name)
+	case "list":
+		return fmt.Sprintf("list (type = '%s', name = '%s', length = '%s')",
+			f.Type, f.Name, f.Expr)
+	case "localfield":
+		return fmt.Sprintf("localfield (type = '%s', name = '%s')",
+			f.Type, f.Name)
+	case "exprfield":
+		return fmt.Sprintf("exprfield (type = '%s', name = '%s', expr = '%s')",
+			f.Type, f.Name, f.Expr)
+	case "valueparam":
+		return fmt.Sprintf("valueparam (type = '%s', name = '%s', list = '%s')",
+			f.ValueMaskType, f.ValueMaskName, f.ValueListName)
+	case "switch":
+		bitcases := make([]string, len(f.Bitcases))
+		for i, bitcase := range f.Bitcases {
+			bitcases[i] = bitcase.StringPrefix("\t")
+		}
+		return fmt.Sprintf("switch (name = '%s', expr = '%s')\n\t%s",
+			f.Name, f.Expr, strings.Join(bitcases, "\n\t"))
+	default:
+		log.Panicf("Unrecognized field element: %s", f.XMLName.Local)
+	}
+
+	panic("unreachable")
+}
+
+// Bitcase represents a single expression followed by any number of fields.
+// Namely, if the switch's expression (all bitcases are inside a switch),
+// and'd with the bitcase's expression is equal to the bitcase expression,
+// then the fields should be included in its parent structure.
+// Note that since a bitcase is unique in that expressions and fields are
+// siblings, we must exhaustively search for one of them. Essentially,
+// it's the closest thing to a Union I can get to in Go without interfaces.
+// Would an '<expression>' tag have been too much to ask? :-(
+type Bitcase struct {
+	Fields []*Field `xml:",any"`
+
+	// All the different expressions.
+	// When it comes time to choose one, use the 'Expr' method.
+	ExprOp *Expression `xml:"op"`
+	ExprUnOp *Expression `xml:"unop"`
+	ExprField *Expression `xml:"fieldref"`
+	ExprValue *Expression `xml:"value"`
+	ExprBit *Expression `xml:"bit"`
+	ExprEnum *Expression `xml:"enumref"`
+	ExprSum *Expression `xml:"sumof"`
+	ExprPop *Expression `xml:"popcount"`
+}
+
+// StringPrefix is for debugging purposes only.
+// StringPrefix takes a string to prefix to every extra line for formatting.
+func (b *Bitcase) StringPrefix(prefix string) string {
+	fields := make([]string, len(b.Fields))
+	for i, field := range b.Fields {
+		fields[i] = fmt.Sprintf("%s%s", prefix, field)
+	}
+	return fmt.Sprintf("%s\n\t%s%s", b.Expr(), prefix,
+		strings.Join(fields, "\n\t"))
+}
+
+// Expr chooses the only non-nil Expr* field from Bitcase.
+// Panic if there is more than one non-nil expression.
+func (b *Bitcase) Expr() *Expression {
+	choices := []*Expression{
+		b.ExprOp, b.ExprUnOp, b.ExprField, b.ExprValue,
+		b.ExprBit, b.ExprEnum, b.ExprSum, b.ExprPop,
+	}
+
+	var choice *Expression = nil
+	numNonNil := 0
+	for _, c := range choices {
+		if c != nil {
+			numNonNil++
+			choice = c
+		}
+	}
+
+	if choice == nil {
+		log.Panicf("No top level expression found in a bitcase.")
+	}
+	if numNonNil > 1 {
+		log.Panicf("More than one top-level expression was found in a bitcase.")
+	}
+	return choice
+}