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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 "&":
return wrap(operand1.Eval() & operand2.Eval())
case "<<":
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")
}
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