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/* Copyright 2018 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use crate::{BinaryReader, ConstExpr, FromReader, GlobalType, Result, SectionLimited};

/// Represents a core WebAssembly global.
#[derive(Debug, Copy, Clone)]
pub struct Global<'a> {
    /// The global's type.
    pub ty: GlobalType,
    /// The global's initialization expression.
    pub init_expr: ConstExpr<'a>,
}

/// A reader for the global section of a WebAssembly module.
pub type GlobalSectionReader<'a> = SectionLimited<'a, Global<'a>>;

impl<'a> FromReader<'a> for Global<'a> {
    fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {
        let ty = reader.read()?;
        let init_expr = reader.read()?;
        Ok(Global { ty, init_expr })
    }
}

impl<'a> FromReader<'a> for GlobalType {
    fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {
        Ok(GlobalType {
            content_type: reader.read()?,
            mutable: match reader.read_u8()? {
                0x00 => false,
                0x01 => true,
                _ => bail!(reader.original_position() - 1, "malformed mutability",),
            },
        })
    }
}