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package cgo
// This file implements a parser of a subset of the C language, just enough to
// parse common #define statements to Go constant expressions.
import (
"go/ast"
"go/token"
"strings"
)
// parseConst parses the given string as a C constant.
func parseConst(pos token.Pos, value string) *ast.BasicLit {
for len(value) != 0 && value[0] == '(' && value[len(value)-1] == ')' {
value = strings.TrimSpace(value[1 : len(value)-1])
}
if len(value) == 0 {
// Pretend it doesn't exist at all.
return nil
}
// For information about integer literals:
// https://en.cppreference.com/w/cpp/language/integer_literal
if value[0] == '"' {
// string constant
return &ast.BasicLit{ValuePos: pos, Kind: token.STRING, Value: value}
}
if value[0] == '\'' {
// char constant
return &ast.BasicLit{ValuePos: pos, Kind: token.CHAR, Value: value}
}
// assume it's a number (int or float)
value = strings.Replace(value, "'", "", -1) // remove ' chars
value = strings.TrimRight(value, "lu") // remove llu suffixes etc.
// find the first non-number
nonnum := byte(0)
for i := 0; i < len(value); i++ {
if value[i] < '0' || value[i] > '9' {
nonnum = value[i]
break
}
}
// determine number type based on the first non-number
switch nonnum {
case 0:
// no non-number found, must be an integer
return &ast.BasicLit{ValuePos: pos, Kind: token.INT, Value: value}
case 'x', 'X':
// hex integer constant
// TODO: may also be a floating point number per C++17.
return &ast.BasicLit{ValuePos: pos, Kind: token.INT, Value: value}
case '.', 'e':
// float constant
value = strings.TrimRight(value, "fFlL")
return &ast.BasicLit{ValuePos: pos, Kind: token.FLOAT, Value: value}
default:
// unknown type, ignore
}
return nil
}
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