8 files changed, 1057 insertions, 0 deletions
diff --git a/nexgb/xgbgen/context.go b/nexgb/xgbgen/context.go
new file mode 100644
index 0000000..e5acb12
--- /dev/null
+++ b/nexgb/xgbgen/context.go
@@ -0,0 +1,89 @@
+package main
+
+import (
+	"bytes"
+	"encoding/xml"
+	"fmt"
+	"log"
+	"strings"
+)
+
+type Context struct {
+	xml *XML
+	out *bytes.Buffer
+}
+
+func newContext() *Context {
+	return &Context{
+		xml: &XML{},
+		out: bytes.NewBuffer([]byte{}),
+	}
+}
+
+// Putln calls put and adds a new line to the end of 'format'.
+func (c *Context) Putln(format string, v ...interface{}) {
+	c.Put(format + "\n", v...)
+}
+
+// Put is a short alias to write to 'out'.
+func (c *Context) Put(format string, v ...interface{}) {
+	_, err := c.out.WriteString(fmt.Sprintf(format, v...))
+	if err != nil {
+		log.Fatalf("There was an error writing to context buffer: %s", err)
+	}
+}
+
+// TypePrefix searches the parsed XML for a type matching 'needle'.
+// It then returns the appropriate prefix to be used in source code.
+// Note that the core X protocol *is* a namespace, but does not have a prefix.
+// Also note that you should probably check the BaseTypeMap and TypeMap
+// before calling this function.
+func (c *Context) TypePrefix(needle Type) string {
+	// If this is xproto, quit. No prefixes needed.
+	if c.xml.Header == "xproto" {
+		return ""
+	}
+
+	// First check for the type in the current namespace.
+	if c.xml.HasType(needle) {
+		return strings.Title(c.xml.Header)
+	}
+
+	// Now check each of the imports...
+	for _, imp := range c.xml.Imports {
+		if imp.xml.Header != "xproto" && imp.xml.HasType(needle) {
+			return strings.Title(imp.xml.Header)
+		}
+	}
+
+	return ""
+}
+
+// Translate is the big daddy of them all. It takes in an XML byte slice
+// and writes Go code to the 'out' buffer.
+func (c *Context) Translate(xmlBytes []byte) {
+	err := xml.Unmarshal(xmlBytes, c.xml)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Parse all imports
+	c.xml.Imports.Eval()
+
+	// Make sure all top level enumerations have expressions
+	// (For when there are empty items.)
+	c.xml.Enums.Eval()
+
+	// It's Morphin' Time!
+	c.xml.Morph(c)
+
+	// for _, req := range c.xml.Requests { 
+		// if req.Name != "CreateContext" && req.Name != "MakeCurrent" { 
+			// continue 
+		// } 
+		// log.Println(req.Name) 
+		// for _, field := range req.Fields { 
+			// log.Println("\t", field.XMLName.Local, field.Type.Morph(c)) 
+		// } 
+	// } 
+}
diff --git a/nexgb/xgbgen/go.go b/nexgb/xgbgen/go.go
new file mode 100644
index 0000000..eb3f0fb
--- /dev/null
+++ b/nexgb/xgbgen/go.go
@@ -0,0 +1,255 @@
+package main
+/*
+	To the best of my ability, these are all of the Go specific formatting
+	functions. If I've designed xgbgen correctly, this should be only the
+	place that you change things to generate code for a new language.
+
+	This file is organized as follows:
+
+	* Imports and helper variables.
+	* Manual type and name override maps.
+	* Helper morphing functions.
+	* Morphing functions for each "unit".
+	* Morphing functions for collections of "units".
+*/
+
+import (
+	"strings"
+)
+
+/******************************************************************************/
+// Manual type and name overrides.
+/******************************************************************************/
+
+// BaseTypeMap is a map from X base types to Go types.
+// X base types should correspond to the smallest set of X types
+// that can be used to rewrite ALL X types in terms of Go types.
+// That is, if you remove any of the following types, at least one
+// XML protocol description will produce an invalid Go program.
+// The types on the left *never* show themselves in the source.
+var BaseTypeMap = map[string]string{
+	"CARD8": "byte",
+	"CARD16": "uint16",
+	"CARD32": "uint32",
+	"INT8": "int8",
+	"INT16": "int16",
+	"INT32": "int32",
+	"BYTE": "byte",
+	"BOOL": "bool",
+	"float": "float64",
+	"double": "float64",
+}
+
+// TypeMap is a map from types in the XML to type names that is used
+// in the functions that follow. Basically, every occurrence of the key
+// type is replaced with the value type.
+var TypeMap = map[string]string{
+	"VISUALTYPE": "VisualInfo",
+	"DEPTH": "DepthInfo",
+	"SCREEN": "ScreenInfo",
+	"Setup": "SetupInfo",
+}
+
+// NameMap is the same as TypeMap, but for names.
+var NameMap = map[string]string{ }
+
+/******************************************************************************/
+// Helper functions that aide in morphing repetive constructs.
+// i.e., "structure contents", expressions, type and identifier names, etc.
+/******************************************************************************/
+
+// Morph changes every TYPE (not names) into something suitable
+// for your language.
+func (typ Type) Morph(c *Context) string {
+	t := string(typ)
+
+	// If this is a base type, then write the raw Go type.
+	if newt, ok := BaseTypeMap[t]; ok {
+		return newt
+	}
+
+	// If it's in the type map, use that translation.
+	if newt, ok := TypeMap[t]; ok {
+		return newt
+	}
+
+	// If it's a resource type, just use 'Id'.
+	if c.xml.IsResource(typ) {
+		return "Id"
+	}
+
+	// If there's a namespace to this type, just use it and be done.
+	if colon := strings.Index(t, ":"); colon > -1 {
+		namespace := t[:colon]
+		rest := t[colon+1:]
+		return splitAndTitle(namespace) + splitAndTitle(rest)
+	}
+
+	// Since there is no namespace, we need to look for a namespace
+	// in the current context.
+	return c.TypePrefix(typ) + splitAndTitle(t)
+}
+
+// Morph changes every identifier (NOT type) into something suitable
+// for your language.
+func (name Name) Morph(c *Context) string {
+	n := string(name)
+
+	// If it's in the name map, use that translation.
+	if newn, ok := NameMap[n]; ok {
+		return newn
+	}
+
+	return splitAndTitle(n)
+}
+
+/******************************************************************************/
+// Per element morphing.
+// Below are functions that morph a single unit.
+/******************************************************************************/
+
+// Import morphing.
+func (imp *Import) Morph(c *Context) {
+	c.Putln("// import \"%s\"", imp.Name)
+}
+
+// Enum morphing.
+func (enum *Enum) Morph(c *Context) {
+	c.Putln("const (")
+	for _, item := range enum.Items {
+		c.Putln("%s%s = %d", enum.Name.Morph(c), item.Name.Morph(c),
+			item.Expr.Eval())
+	}
+	c.Putln(")\n")
+}
+
+// Xid morphing.
+func (xid *Xid) Morph(c *Context) {
+	// Don't emit anything for xid types for now.
+	// We're going to force them all to simply be 'Id'
+	// to avoid excessive type converting.
+	// c.Putln("type %s Id", xid.Name.Morph(c)) 
+}
+
+// TypeDef morphing.
+func (typedef *TypeDef) Morph(c *Context) {
+	c.Putln("type %s %s", typedef.Old.Morph(c), typedef.New.Morph(c))
+}
+
+// Struct morphing.
+func (strct *Struct) Morph(c *Context) {
+}
+
+// Union morphing.
+func (union *Union) Morph(c *Context) {
+}
+
+// Request morphing.
+func (request *Request) Morph(c *Context) {
+}
+
+// Event morphing.
+func (ev *Event) Morph(c *Context) {
+}
+
+// EventCopy morphing.
+func (evcopy *EventCopy) Morph(c *Context) {
+}
+
+// Error morphing.
+func (err *Error) Morph(c *Context) {
+}
+
+// ErrorCopy morphing.
+func (errcopy *ErrorCopy) Morph(c *Context) {
+}
+
+/******************************************************************************/
+// Collection morphing.
+// Below are functions that morph a collections of units.
+// Most of these can probably remain unchanged, but they are useful if you
+// need to group all of some "unit" in a single block or something.
+/******************************************************************************/
+func (imports Imports) Morph(c *Context) {
+	if len(imports) == 0 {
+		return
+	}
+
+	c.Putln("// Imports are not required for XGB since everything is in")
+	c.Putln("// a single package. Still these may be useful for ")
+	c.Putln("// reference purposes.")
+	for _, imp := range imports {
+		imp.Morph(c)
+	}
+}
+
+func (enums Enums) Morph(c *Context) {
+	c.Putln("// Enums\n")
+	for _, enum := range enums {
+		enum.Morph(c)
+	}
+}
+
+func (xids Xids) Morph(c *Context) {
+	c.Putln("// Xids\n")
+	for _, xid := range xids {
+		xid.Morph(c)
+	}
+}
+
+func (typedefs TypeDefs) Morph(c *Context) {
+	c.Putln("// TypeDefs\n")
+	for _, typedef := range typedefs {
+		typedef.Morph(c)
+	}
+}
+
+func (strct Structs) Morph(c *Context) {
+	c.Putln("// Structs\n")
+	for _, typedef := range strct {
+		typedef.Morph(c)
+	}
+}
+
+func (union Unions) Morph(c *Context) {
+	c.Putln("// Unions\n")
+	for _, typedef := range union {
+		typedef.Morph(c)
+	}
+}
+
+func (request Requests) Morph(c *Context) {
+	c.Putln("// Requests\n")
+	for _, typedef := range request {
+		typedef.Morph(c)
+	}
+}
+
+func (event Events) Morph(c *Context) {
+	c.Putln("// Events\n")
+	for _, typedef := range event {
+		typedef.Morph(c)
+	}
+}
+
+func (evcopy EventCopies) Morph(c *Context) {
+	c.Putln("// Event Copies\n")
+	for _, typedef := range evcopy {
+		typedef.Morph(c)
+	}
+}
+
+func (err Errors) Morph(c *Context) {
+	c.Putln("// Errors\n")
+	for _, typedef := range err {
+		typedef.Morph(c)
+	}
+}
+
+func (errcopy ErrorCopies) Morph(c *Context) {
+	c.Putln("// Error copies\n")
+	for _, typedef := range errcopy {
+		typedef.Morph(c)
+	}
+}
+
diff --git a/nexgb/xgbgen/main.go b/nexgb/xgbgen/main.go
new file mode 100644
index 0000000..69579a4
--- /dev/null
+++ b/nexgb/xgbgen/main.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"flag"
+	"io/ioutil"
+	"log"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+var (
+	protoPath = flag.String("proto-path",
+		"/usr/share/xcb", "path to directory of X protocol XML files")
+	gofmt = flag.Bool("gofmt", true,
+		"When disabled, gofmt will not be run before outputting Go code")
+)
+
+func usage() {
+	basename := os.Args[0]
+	if lastSlash := strings.LastIndex(basename, "/"); lastSlash > -1 {
+		basename = basename[lastSlash+1:]
+	}
+	log.Printf("Usage: %s [flags] xml-file", basename)
+	flag.PrintDefaults()
+	os.Exit(1)
+}
+
+func init() {
+	log.SetFlags(0)
+}
+
+func main() {
+	flag.Usage = usage
+	flag.Parse()
+
+	if flag.NArg() != 1 {
+		log.Printf("A single XML protocol file can be processed at once.")
+		flag.Usage()
+	}
+
+	// Read the single XML file into []byte
+	xmlBytes, err := ioutil.ReadFile(flag.Arg(0))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Initialize the buffer, parse it, and filter it through gofmt.
+	c := newContext()
+	c.Translate(xmlBytes)
+
+	if !*gofmt {
+		c.out.WriteTo(os.Stdout)
+	} else {
+		cmdGofmt := exec.Command("gofmt")
+		cmdGofmt.Stdin = c.out
+		cmdGofmt.Stdout = os.Stdout
+		err = cmdGofmt.Run()
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
+}
+
diff --git a/nexgb/xgbgen/misc.go b/nexgb/xgbgen/misc.go
new file mode 100644
index 0000000..9adcf5d
--- /dev/null
+++ b/nexgb/xgbgen/misc.go
@@ -0,0 +1,44 @@
+package main
+
+import (
+	"regexp"
+	"strings"
+)
+
+// AllCaps is a regex to test if a string identifier is made of
+// all upper case letters.
+var AllCaps = regexp.MustCompile("^[A-Z0-9]+$")
+
+// popCount counts number of bits 'set' in mask.
+func popCount(mask uint) uint {
+	m := uint32(mask)
+	n := uint(0)
+	for i := uint32(0); i < 32; i++ {
+		if m&(1<<i) != 0 {
+			n++
+		}
+	}
+	return n
+}
+
+// splitAndTitle takes a string, splits it by underscores, capitalizes the
+// first letter of each chunk, and smushes'em back together.
+func splitAndTitle(s string) string {
+	// If the string is all caps, lower it and capitalize first letter.
+	if AllCaps.MatchString(s) {
+		return strings.Title(strings.ToLower(s))
+	}
+
+	// If the string has no underscores, leave it be.
+	if i := strings.Index(s, "_"); i == -1 {
+		return s
+	}
+
+	// Now split the name at underscores, capitalize the first
+	// letter of each chunk, and smush'em back together.
+	chunks := strings.Split(s, "_")
+	for i, chunk := range chunks {
+		chunks[i] = strings.Title(strings.ToLower(chunk))
+	}
+	return strings.Join(chunks, "")
+}
diff --git a/nexgb/xgbgen/xgbgen b/nexgb/xgbgen/xgbgen
new file mode 100755
index 0000000..ef33abc
--- /dev/null
+++ b/nexgb/xgbgen/xgbgen
diff --git a/nexgb/xgbgen/xml.go b/nexgb/xgbgen/xml.go
new file mode 100644
index 0000000..0f632b4
--- /dev/null
+++ b/nexgb/xgbgen/xml.go
@@ -0,0 +1,298 @@
+package main
+
+import (
+	"encoding/xml"
+	"io/ioutil"
+	"log"
+	"time"
+)
+
+type XML struct {
+	// Root 'xcb' element properties.
+	XMLName xml.Name `xml:"xcb"`
+	Header string `xml:"header,attr"`
+	ExtensionXName string `xml:"extension-xname,attr"`
+	ExtensionName string `xml:"extension-name,attr"`
+	MajorVersion string `xml:"major-version,attr"`
+	MinorVersion string `xml:"minor-version,attr"`
+
+	// Types for all top-level elements.
+	// First are the simple ones.
+	Imports Imports `xml:"import"`
+	Enums Enums `xml:"enum"`
+	Xids Xids `xml:"xidtype"`
+	XidUnions Xids `xml:"xidunion"`
+	TypeDefs TypeDefs `xml:"typedef"`
+	EventCopies EventCopies `xml:"eventcopy"`
+	ErrorCopies ErrorCopies `xml:"errorcopy"`
+
+	// Here are the complex ones, i.e., anything with "structure contents"
+	Structs Structs `xml:"struct"`
+	Unions Unions `xml:"union"`
+	Requests Requests `xml:"request"`
+	Events Events `xml:"event"`
+	Errors Errors `xml:"error"`
+}
+
+// Morph cascades down all of the XML and calls each type's corresponding
+// Morph function with itself as an argument (the context).
+func (x *XML) Morph(c *Context) {
+	// Start the header...
+	c.Putln("package xgb")
+	c.Putln("/*")
+	c.Putln("\tX protocol API for '%s.xml'.", c.xml.Header)
+	c.Putln("\tThis file is automatically generated. Edit at your own peril!")
+	c.Putln("\tGenerated on %s",
+		time.Now().Format("Jan 2, 2006 at 3:04:05pm MST"))
+	c.Putln("*/")
+	c.Putln("")
+
+	x.Imports.Morph(c)
+	c.Putln("")
+
+	x.Enums.Morph(c)
+	c.Putln("")
+
+	x.Xids.Morph(c)
+	c.Putln("")
+
+	x.XidUnions.Morph(c)
+	c.Putln("")
+
+	x.TypeDefs.Morph(c)
+	c.Putln("")
+
+	x.Structs.Morph(c)
+	c.Putln("")
+
+	x.Unions.Morph(c)
+	c.Putln("")
+
+	x.Requests.Morph(c)
+	c.Putln("")
+
+	x.Events.Morph(c)
+	c.Putln("")
+
+	x.Errors.Morph(c)
+	c.Putln("")
+
+	x.EventCopies.Morph(c)
+	c.Putln("")
+
+	x.ErrorCopies.Morph(c)
+	c.Putln("")
+}
+
+// IsResource returns true if the 'needle' type is a resource type.
+// i.e., an "xid"
+func (x *XML) IsResource(needle Type) bool {
+	for _, xid := range x.Xids {
+		if needle == xid.Name {
+			return true
+		}
+	}
+	for _, xidunion := range x.XidUnions {
+		if needle == xidunion.Name {
+			return true
+		}
+	}
+	for _, imp := range x.Imports {
+		if imp.xml.IsResource(needle) {
+			return true
+		}
+	}
+	return false
+}
+
+// HasType returns true if the 'needle' type can be found in the protocol
+// description represented by 'x'.
+func (x *XML) HasType(needle Type) bool {
+	for _, enum := range x.Enums {
+		if needle == enum.Name {
+			return true
+		}
+	}
+	for _, xid := range x.Xids {
+		if needle == xid.Name {
+			return true
+		}
+	}
+	for _, xidunion := range x.XidUnions {
+		if needle == xidunion.Name {
+			return true
+		}
+	}
+	for _, typedef := range x.TypeDefs {
+		if needle == typedef.New {
+			return true
+		}
+	}
+	for _, evcopy := range x.EventCopies {
+		if needle == evcopy.Name {
+			return true
+		}
+	}
+	for _, errcopy := range x.ErrorCopies {
+		if needle == errcopy.Name {
+			return true
+		}
+	}
+	for _, strct := range x.Structs {
+		if needle == strct.Name {
+			return true
+		}
+	}
+	for _, union := range x.Unions {
+		if needle == union.Name {
+			return true
+		}
+	}
+	for _, ev := range x.Events {
+		if needle == ev.Name {
+			return true
+		}
+	}
+	for _, err := range x.Errors {
+		if needle == err.Name {
+			return true
+		}
+	}
+
+	return false
+}
+
+type Name string
+
+type Type string
+
+type Imports []*Import
+
+func (imports Imports) Eval() {
+	for _, imp := range imports {
+		xmlBytes, err := ioutil.ReadFile(*protoPath + "/" + imp.Name + ".xml")
+		if err != nil {
+			log.Fatalf("Could not read X protocol description for import " +
+				"'%s' because: %s", imp.Name, err)
+		}
+
+		imp.xml = &XML{}
+		err = xml.Unmarshal(xmlBytes, imp.xml)
+		if err != nil {
+			log.Fatal("Could not parse X protocol description for import " +
+				"'%s' because: %s", imp.Name, err)
+		}
+	}
+}
+
+type Import struct {
+	Name string `xml:",chardata"`
+	xml *XML `xml:"-"`
+}
+
+type Enums []Enum
+
+// Eval on the list of all enum types goes through and forces every enum
+// item to have a valid expression.
+// This is necessary because when an item is empty, it is defined to have
+// the value of "one more than that of the previous item, or 0 for the first
+// item".
+func (enums Enums) Eval() {
+	for _, enum := range enums {
+		nextValue := uint(0)
+		for _, item := range enum.Items {
+			if item.Expr == nil {
+				item.Expr = newValueExpression(nextValue)
+				nextValue++
+			} else {
+				nextValue = item.Expr.Eval() + 1
+			}
+		}
+	}
+}
+
+type Enum struct {
+	Name Type `xml:"name,attr"`
+	Items []*EnumItem `xml:"item"`
+}
+
+type EnumItem struct {
+	Name Name `xml:"name,attr"`
+	Expr *Expression `xml:",any"`
+}
+
+type Xids []*Xid
+
+type Xid struct {
+	XMLName xml.Name
+	Name Type `xml:"name,attr"`
+}
+
+type TypeDefs []*TypeDef
+
+type TypeDef struct {
+	Old Type `xml:"oldname,attr"`
+	New Type `xml:"newname,attr"`
+}
+
+type EventCopies []*EventCopy
+
+type EventCopy struct {
+	Name Type `xml:"name,attr"`
+	Number string `xml:"number,attr"`
+	Ref Type `xml:"ref,attr"`
+}
+
+type ErrorCopies []*ErrorCopy
+
+type ErrorCopy struct {
+	Name Type `xml:"name,attr"`
+	Number string `xml:"number,attr"`
+	Ref Type `xml:"ref,attr"`
+}
+
+type Structs []*Struct
+
+type Struct struct {
+	Name Type `xml:"name,attr"`
+	Fields []*Field `xml:",any"`
+}
+
+type Unions []*Union
+
+type Union struct {
+	Name Type `xml:"name,attr"`
+	Fields []*Field `xml:",any"`
+}
+
+type Requests []*Request
+
+type Request struct {
+	Name Type `xml:"name,attr"`
+	Opcode int `xml:"opcode,attr"`
+	Combine bool `xml:"combine-adjacent,attr"`
+	Fields []*Field `xml:",any"`
+	Reply *Reply `xml:"reply"`
+}
+
+type Reply struct {
+	Fields []*Field `xml:",any"`
+}
+
+type Events []*Event
+
+type Event struct {
+	Name Type `xml:"name,attr"`
+	Number int `xml:"number,attr"`
+	NoSequence bool `xml:"no-sequence-number,true"`
+	Fields []*Field `xml:",any"`
+}
+
+type Errors []*Error
+
+type Error struct {
+	Name Type `xml:"name,attr"`
+	Number int `xml:"number,attr"`
+	Fields []*Field `xml:",any"`
+}
+
diff --git a/nexgb/xgbgen/xml_expression.go b/nexgb/xgbgen/xml_expression.go
new file mode 100644
index 0000000..dd32512
--- /dev/null
+++ b/nexgb/xgbgen/xml_expression.go
@@ -0,0 +1,160 @@
+package main
+
+import (
+	"encoding/xml"
+	"fmt"
+	"log"
+	"strconv"
+)
+
+type Expression struct {
+	XMLName xml.Name
+
+	Exprs []*Expression `xml:",any"`
+
+	Data string `xml:",chardata"`
+	Op string `xml:"op,attr"`
+	Ref string `xml:"ref,attr"`
+}
+
+func newValueExpression(v uint) *Expression {
+	return &Expression{
+		XMLName: xml.Name{Local: "value"},
+		Data: fmt.Sprintf("%d", v),
+	}
+}
+
+// String is for debugging. For actual use, please use 'Morph'.
+func (e *Expression) String() string {
+	switch e.XMLName.Local {
+	case "op":
+		return fmt.Sprintf("(%s %s %s)", e.Exprs[0], e.Op, e.Exprs[1])
+	case "unop":
+		return fmt.Sprintf("(%s (%s))", e.Op, e.Exprs[0])
+	case "popcount":
+		return fmt.Sprintf("popcount(%s)", e.Exprs[0])
+	case "fieldref":
+		fallthrough
+	case "value":
+		return fmt.Sprintf("%s", e.Data)
+	case "bit":
+		return fmt.Sprintf("(1 << %s)", e.Data)
+	case "enumref":
+		return fmt.Sprintf("%s%s", e.Ref, e.Data)
+	case "sumof":
+		return fmt.Sprintf("sum(%s)", e.Ref)
+	default:
+		log.Panicf("Unrecognized expression element: %s", e.XMLName.Local)
+	}
+
+	panic("unreachable")
+}
+
+// Eval is used to *attempt* to compute a concrete value for a particular
+// expression. This is used in the initial setup to instantiate values for
+// empty items in enums.
+// We can't compute a concrete value for expressions that rely on a context,
+// i.e., some field value.
+func (e *Expression) Eval() uint {
+	switch e.XMLName.Local {
+	case "op":
+		if len(e.Exprs) != 2 {
+			log.Panicf("'op' found %d expressions; expected 2.", len(e.Exprs))
+		}
+		return e.BinaryOp(e.Exprs[0], e.Exprs[1]).Eval()
+	case "unop":
+		if len(e.Exprs) != 1 {
+			log.Panicf("'unop' found %d expressions; expected 1.", len(e.Exprs))
+		}
+		return e.UnaryOp(e.Exprs[0]).Eval()
+	case "popcount":
+		if len(e.Exprs) != 1 {
+			log.Panicf("'popcount' found %d expressions; expected 1.",
+				len(e.Exprs))
+		}
+		return popCount(e.Exprs[0].Eval())
+	case "value":
+		val, err := strconv.Atoi(e.Data)
+		if err != nil {
+			log.Panicf("Could not convert '%s' in 'value' expression to int.",
+				e.Data)
+		}
+		return uint(val)
+	case "bit":
+		bit, err := strconv.Atoi(e.Data)
+		if err != nil {
+			log.Panicf("Could not convert '%s' in 'bit' expression to int.",
+				e.Data)
+		}
+		if bit < 0 || bit > 31 {
+			log.Panicf("A 'bit' literal must be in the range [0, 31], but " +
+				" is %d", bit)
+		}
+		return 1 << uint(bit)
+	case "fieldref":
+		log.Panicf("Cannot compute concrete value of 'fieldref' in " +
+			"expression '%s'.", e)
+	case "enumref":
+		log.Panicf("Cannot compute concrete value of 'enumref' in " +
+			"expression '%s'.", e)
+	case "sumof":
+		log.Panicf("Cannot compute concrete value of 'sumof' in " +
+			"expression '%s'.", e)
+	}
+
+	log.Panicf("Unrecognized tag '%s' in expression context. Expected one of " +
+		"op, fieldref, value, bit, enumref, unop, sumof or popcount.",
+		e.XMLName.Local)
+	panic("unreachable")
+}
+
+func (e *Expression) BinaryOp(operand1, operand2 *Expression) *Expression {
+	if e.XMLName.Local != "op" {
+		log.Panicf("Cannot perform binary operation on non-op expression: %s",
+			e.XMLName.Local)
+	}
+	if len(e.Op) == 0 {
+		log.Panicf("Cannot perform binary operation without operator for: %s",
+			e.XMLName.Local)
+	}
+
+	wrap := newValueExpression
+	switch e.Op {
+	case "+":
+		return wrap(operand1.Eval() + operand2.Eval())
+	case "-":
+		return wrap(operand1.Eval() + operand2.Eval())
+	case "*":
+		return wrap(operand1.Eval() * operand2.Eval())
+	case "/":
+		return wrap(operand1.Eval() / operand2.Eval())
+	case "&amp;":
+		return wrap(operand1.Eval() & operand2.Eval())
+	case "&lt;&lt;":
+		return wrap(operand1.Eval() << operand2.Eval())
+	}
+
+	log.Panicf("Invalid binary operator '%s' for '%s' expression.",
+		e.Op, e.XMLName.Local)
+	panic("unreachable")
+}
+
+func (e *Expression) UnaryOp(operand *Expression) *Expression {
+	if e.XMLName.Local != "unop" {
+		log.Panicf("Cannot perform unary operation on non-unop expression: %s",
+			e.XMLName.Local)
+	}
+	if len(e.Op) == 0 {
+		log.Panicf("Cannot perform unary operation without operator for: %s",
+			e.XMLName.Local)
+	}
+
+	switch e.Op {
+	case "~":
+		return newValueExpression(^operand.Eval())
+	}
+
+	log.Panicf("Invalid unary operator '%s' for '%s' expression.",
+		e.Op, e.XMLName.Local)
+	panic("unreachable")
+}
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
+}