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/// A namespace for the canonical lowering operations used by host side.
public enum CanonicalLowering {
/// Lowers a Swift String value to a pair of a pointer and a length
/// The pointer points to a guest memory region that contains the encoded string value.
public static func lowerString(
_ value: String, context: CanonicalCallContext
) throws -> (pointer: UInt32, length: UInt32) {
guard context.options.stringEncoding == .utf8 else {
throw CanonicalABIError(description: "Unsupported string encoding: \(context.options.stringEncoding)")
}
let bytes = value.utf8
let newBuffer = try context.realloc(
old: 0, oldSize: 0, oldAlign: 1, newSize: UInt32(bytes.count)
)
newBuffer.withHostPointer { newBuffer in
UnsafeMutableRawBufferPointer(start: newBuffer, count: bytes.count).copyBytes(from: bytes)
}
return (newBuffer.offset, UInt32(bytes.count))
}
/// Lowers a Swift Array value to a pair of a pointer and a length.
///
/// - Parameters:
/// - value: A Swift Array value to be lowered.
/// - elementSize: A byte size of an element of the array value in lowered representation.
/// - elementAlignment: A byte alignment of an element of the array value in lowered representation.
/// - storeElement: A closure that stores an element to the given pointer.
/// - context: A canonical call context.
/// - Returns: A pair of a pointer and a length.
public static func lowerList<Element>(
_ value: [Element], elementSize: UInt32, elementAlignment: UInt32,
storeElement: (Element, UnsafeGuestRawPointer) throws -> Void,
context: CanonicalCallContext
) throws -> (pointer: UInt32, length: UInt32) {
let byteLength = UInt32(value.count) * elementSize
let newBuffer = try context.realloc(
old: 0, oldSize: 0, oldAlign: elementAlignment, newSize: byteLength
)
for (i, element) in value.enumerated() {
try storeElement(element, newBuffer.advanced(by: elementSize * UInt32(i)))
}
return (newBuffer.offset, UInt32(value.count))
}
}
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